EP4251569A2 - Borophene synthesis - Google Patents

Borophene synthesis

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Publication number
EP4251569A2
EP4251569A2 EP22706539.8A EP22706539A EP4251569A2 EP 4251569 A2 EP4251569 A2 EP 4251569A2 EP 22706539 A EP22706539 A EP 22706539A EP 4251569 A2 EP4251569 A2 EP 4251569A2
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EP
European Patent Office
Prior art keywords
boron
bonds
heteroatom
clusters
multitude
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP22706539.8A
Other languages
German (de)
French (fr)
Inventor
Georg Duesberg
Wilhelm AUWAERTER
Hermann Sachdev
Marc GONZÁLEZ CUXAT
Knud Johannes SEUFERT
Valeria CHESNYAK
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Technische Universitaet Muenchen
Universitaet der Bundeswehr Muenchen
Original Assignee
Technische Universitaet Muenchen
Universitaet der Bundeswehr Muenchen
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Filing date
Publication date
Application filed by Technische Universitaet Muenchen, Universitaet der Bundeswehr Muenchen filed Critical Technische Universitaet Muenchen
Publication of EP4251569A2 publication Critical patent/EP4251569A2/en
Pending legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B35/00—Boron; Compounds thereof
    • C01B35/02—Boron; Borides
    • C01B35/023—Boron
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/20—Particle morphology extending in two dimensions, e.g. plate-like

Definitions

  • the invention relates to a method for the production of a structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron- containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B- heteroatom bonds are connected by B-B bonds, as well as a product comprising a structure containing at
  • Borophenes which comprise in their definition according to the state of the art usually atomically thin sheets formed by boron, are a prominent member of the family of synthetic 2D materials due to their anisotropic and polymorphic structures and superlative strength and stiffness compared to graphene, as disclosed in Mannix, A. J., Zhang, Z., Guisinger, N. P., Yakobson, B. I., & Hersam, M. C. (2018). Borophene is a prototype for synthetic 2D materials development, as described in Nature Nanotechnology, 13(6), 444 ⁇ 150. https://doi.org/10.1038/s41565-018-0157-4.
  • Borophenes can be considered to be of single atomic thickness, but can also be thought to be extended to structures of 2D aspect ratio due to interconnected cluster subunits, still being different from and not resembling known 3D polymorphs of elemental boron.
  • Chemical vapor deposition (CVD) by using specific precursors has shown to be a flexible and scalable growth method, suitable to produce large single 2D crystals, and nowadays is widely used for the synthesis of numerous 2D materials, as e.g. discussed by Cai, Z., Liu, B., Zou, X., & Cheng, H.-M. (2016). Chemical Vapor Deposition Growth and Applications of Two- Dimensional Materials and Their Heterostructures [Review-article] Chemical Reviews, 118(13), 6091-6133. https://doi.org/10.1021/acs.chemrev.7b00536).
  • boron nanostructures yielded amorphous structures, nanotubes and thick planar structures, as e.g. described by Tian, J., Xu, Z., Shen, C, Liu, F., Xu, N., & Gao, H.-J. (2010).
  • One-dimensional boron nanostructures Prediction, synthesis, characterizations, and applications.
  • Nanoscale 2(8), 1375, https://doi.org/10.1039/c0nr00051e, and Tai, G., Hu, T., Zhou, Y., Wang, X., Kong, J., Zeng, T., ... Wang, Q. (2015). Synthesis of Atomically Thin Boron Films on Copper Foils. Angewandte Chemie International Edition, 54(51), 15473-15477. https://doi.org/10.1002/anie.201509285, but none of them produced single-atom-thick B layers. The main reason that explain the current failure is that adequate precursors are yet to be found, and the lack of well-controlled and clean growth conditions.
  • the present inventors found a reliable and more effective method of producing borophenes, and/or boron-heteroatom-domains comprising 2D boron networks, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B- B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron- containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B- B bonds, which enables production of the structures in increased size and high homogeneity and lower density of defects
  • the structures therein do not resemble known 3D polymorphs of elemental boron, but refer to 2D polymorphs, polymorphs with pronounced 2D aspect ratio and their derivates and products. These borophene based structures do also differ from amorphous boron monolayers which in principle might be feasible by CVD, due to their intrinsic 2D structural ordering.
  • the present invention relates to a method for the production of a structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron- heteroatom clusters having B-heteroatom bonds are connected by B-B bonds, the method comprising: contacting at least one borophene
  • the substrate has a temperature in the range of -196 °C to 3000 °C, and deposition of a structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D- network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron- containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having
  • boron-containing precursors can be used to create boron films or boron layers
  • these films or layers created can be amorphous or crystalline and have a 3D connectivity of boron atoms derived from known 3D polytypes of elemental boron.
  • these films or layers do not reveal structures resembling a structure as disclosed herein and obtainable by the present method, resembling pronounced polymorphs with a particular 2D aspect ratio.
  • a product comprising a structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B- B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B-B bonds, particularly produced by the present method, wherein the structure containing at least one borophene
  • Fig. 1 shows schematically growth of a borophene using chemical vapor deposition.
  • Fig. 2 shows schematically possible heterolayer and/or multilayer products that can be produced by the present method.
  • FIG. 3 an exemplary experimental, labscale setup used for producing exemplary products in the present Examples is schematically shown.
  • Fig. 4 depicts images of products obtained in the present examples (Fig. 4 a) and of comparative examples produced in the state of the art (Figs. 4b and 4c according to the above Feng et al., 2016, Nature Chemistry, and the above Mannix et al., 2015 Science).
  • Fig. 5 shows STM images of a borophene - h BN lateral heterostructure produced according to the invention.
  • Clusters can formally be considered as molecular building blocks for forming the present structures, but can also be seen as entities being part of the structures, either 2D or 3D.
  • containing can mean that the different atoms, molecules, groups, etc. are formally contained, but are not necessarily to be seen as separate entities as they can be and normally are of the respective network, etc. This particularly applies to clusters within a network, as they are only formally contained but are not isolated and rather form a part of the network.
  • borophene formation are deemed to be valid to any boron isotope ratio, since they can be provided by the precursor, and even isotopically pure domains and heterodomains are feasible.
  • the present structures also may be applicable to applications where specific properties of the different isotopes are required, e.g. for neutron detection, etc.
  • Borophenes are - single or multiple - layers of regular or defective networks of boron atoms which may be corrugated, i.e. slightly shifted in directions out of the 2D plane in each layer. They are based on structural motifs of boron sheets of single atomic thickness, i.e. form a sort of sheet that can be regarded as quasi two-dimensional. Particularly, layers of borophenes do not have to be atomically "flat", i.e. do not only extend in two dimensions, but still may be described as 2D due to their B-B bonds only being within the layer. Borophenes also can be derived from an array of 2 dimensionally interlinked boron clusters (e.g.
  • intrinsically corrugated, symmetry-reduced - with regular defect positions as well as intrinsically buckling patterns - structures may result from a "two dimensional" boron network, which even can be further modulated by the substrate symmetry.
  • planar or partly planar networks are not excluded.
  • borophenes can also form different polymorphs, which are included as well. Borophenes comprise B-B-bonds of variable strength, and may even consist of mainly B-B-bonds of variable strength, and may or may not have additional electronic interactions with a substrate and/or adatoms, dopants, covering layers, etc., which also can be incorporated into a borophene network, e.g.
  • boron-heteroatom-domains comprising a 2D boron network. It is not excluded that borophenes comprise multiple layers that are e.g. arranged on top of each other, similar to graphene heterostructures. Boron-boron bonds do not only comprise classical covalent bonds within the 2D layer structure, but can also comprise different kinds of bonds, e.g. non-classical multi-center bonds and e.g.
  • Boron-heteroatom-domains comprising a 2D boron network are herein defined structures which contain within the 2D boron network one or more species of heteroatoms on substitutional and/or additional sites and/or do contain heteroatoms strongly linked on the surface, and/or also can have heteroatoms like O or N at the rim or incorporated in the 2D lattice.
  • the 2D boron network is sheet-like in a layer but does not have to be flat. It can be a regular or defective network comprising boron atoms with boron boron bonds. It is of single atomic thickness, and may be corrugated, i.e.
  • boron-heteroatom domains comprising a 2D boron network also encompass borophene- based networks with a variable content of heteroatoms like oxygen, nitrogen, carbon and/or hydrogen, stemming e.g. from impurities and/or residues in the production process, as well as borophene-based networks where doping with heteroatoms is intentionally carried out.
  • One heteroatom or multiple heteroatoms can be included which can be the same or different, i.e. the content thereof is variable.
  • Possible heteroatoms include e.g. nitrogen, hydrogen, oxygen, carbon, halogens, metals, etc., and/or mixtures thereof.
  • the boron- heteroatom-domains comprising a 2D boron network thus include borophene-derived layers with variable content of heteroatoms, as well as borophenes doped with heteroatoms, i.e. wherein the heteroatom is purposely introduced. For example, even boron-heteroatom- domains comprising a 2D boron network with large amounts of heteroatoms are included, as long as boron boron bonds are contained, e.g.
  • the boron-heteroatom-domains comprising a 2D boron network can still be rich in boron with respect to the layer stoichiometry, i.e. contain boron with respect to the boron heteroatom domain with 50 at% or more, e.g. more than 50 at%., preferably more than 60 at.%, more preferably more than 70 at%.
  • boron heteroatom domain with 50 at% or more, e.g. more than 50 at%., preferably more than 60 at.%, more preferably more than 70 at%.
  • higher amounts of heteroatoms are not excluded.
  • heteroatoms in boron-heteroatom-domains are not particularly restricted, and in principle any heteroatom of the periodic system of the elements can be incorporated into a boron- heteroatom domain, and also mixtures of heteroatoms.
  • preferred heteroatoms are chosen from the group consisting of H, D, O, N, C, P, S, Se, and/or Te, particularly H, D, O, N, C, P and/or S.
  • further groups and/or heteroatoms may be attached to heteroatoms, e.g. N, C, P, that may have further possible bonding sites, and such heteroatoms and/or groups are not restricted and can e.g. include hydrogen, D, halogens, amines, alcoholates, organyls, aryls, etc.
  • the boron- containing clusters comprising B-B bonds can comprise at least one heteroatom and/or can also comprise no heteroatom, so that structures with only boron-containing clusters comprising B-B bonds with only boron atoms in the clusters are encompassed, structures wherein all boron-containing clusters comprising B-B bonds comprise at least one heteroatom, and structures where at least one or some boron-containing clusters comprising B-B bonds comprise heteroatoms, and at least one or some boron-containing clusters comprising B-B bonds comprise no heteroatoms.
  • structure of a 2D-network with regard to the structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds is therein meant in the sense that the structure forms a layer that extends in two dimensions, e.g. the x and y plane, although also regular or irregular extensions in the further dimension, e.g. the z plane, will occur due to the clusters, but the clusters themselves are again connected within the sheet, thus leading to a 2D network of high aspect ratio.
  • the structure of a 2D- network containing a multitude of boron-containing clusters comprising B-B bonds forms a layer that also covers a surface, but the bonds within the network do not have to be in direct vicinity of the surface, as different boron-containing clusters can be connected next to the surface, or in a different plane above a surface between different boron containing clusters, e.g. through tips of boron-containing icosahedrons, etc.
  • the structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds also forms a network that is sheet-like in a layer, but is not flat due to clusters contained therein.
  • it can be a regular or defective network comprising boron atoms in clusters with boron boron bonds. It is not of single atomic thickness due to the clusters, but at places can have single atomic thickness, e.g. between clusters or at positions where clusters are bonded. It, like the other structures, can even have vacancies if a structural unit is missing, as also described for borophene.
  • the structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds is at least corrugated at clusters, i.e. slightly shifted in directions out of the 2D plane, but can also be corrugated at other places, e.g. between clusters.
  • the structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds can thus also be seen as quasi two-dimensional, with peaks protruding e.g. at positions of clusters.
  • the clusters are not particularly restricted and can be built form at least 3 atoms, e.g. at least 4 atoms, but also more atoms, like 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more.
  • boron clusters of (B2), B3, B4, B5, Bb, Bg, ..., units can be considered to be formally derived from cluster compounds such as (B2H6), B3H7, B4H10, B5H9, ....B10H14, ...
  • cluster compounds such as (B2H6), B3H7, B4H10, B5H9, ....B10H14, ...
  • clusters like (boron or boron-containing) icosahedral structures like e.g .alpha rhombohedral boron in the 3D case can be considered, in the real formation of the structure of a 2D-network containing a multitude of boron-containing clusters comprising B- B bonds from cluster compounds having e.g.
  • the structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds can also be considered to be derived from a multitude of boron- containing clusters that are connected. While it is not excluded that the structure of a 2D- network containing a multitude of boron-containing clusters comprising B-B bonds comprises only boron atoms, it is also not excluded that one heteroatom or more heteroatoms is contained, that are not restricted and can be the same as in the boron- heteroatom-domain comprising a 2D-network.
  • the cluster In the structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds the cluster cannot be isolated, as they are connected, but they are present in a step before formation of the layer.
  • the bonds between clusters are not particularly restricted and can be connected by B-B bonds or B-heteroatom bonds, depending on the location where clusters are bonded, and B-heteroatom bonds between clusters can e.g. be formed if at least one cluster contains at least one heteroatom.
  • the structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B- heteroatom bonds are connected by B-B bonds is not restricted.
  • structure of a 2D-network containing a multitude of boron-containing clusters comprising B- B bonds defined above
  • structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds
  • structure of a 2D-network is therein meant in the sense that the structure forms a layer that extends in two dimensions, e.g.
  • the clusters being bonded to such a network with B-B bonds at least somewhere, preferably in direct vicinity to the cluster.
  • the same considerations apply to the clusters and the heteroatoms in the structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds as apply to the structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, i.e. will also particularly have a defined 2D aspect ratio, as defined above for other structures.
  • the present method as well as in the present product it is not excluded that, apart from the at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron- containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron- heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron- heteroatom clusters having B-heteroatom bonds are connected by B-B bonds, further heterostructures that do or do not contain boron,
  • the present invention relates to a method for the production of a structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20, e.g.
  • boron atoms and/or a structure of a 2D- network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B-B bonds, on the at least one surface of the substrate, wherein a pressure of the at least one precursor in the gaseous or otherwise atomic- molecular excited state is in the range of 10 10 mbar to 10 bar, and wherein the at least one precursor in the gaseous or otherwise atomic-molecular excited state comprises at least one precursor, chosen from the group of substituted and unsubstituted boranes - including substituted and unsubstituted aminoboranes and substituted and unsubstituted iminoboranes, substituted and unsubstituted heteroboranes, substituted and unsubstituted polyboranes, substituted and unsubstituted poly-boron
  • substituted poly-boron compounds e.g. polyboron halides
  • substituted and unsubstituted organoboron compounds e.g. boron aryls
  • substituted and unsubstituted organopolyboron compounds e.g.
  • polyboron aryls substituted and unsubstituted borazines, substituted and unsubstituted boroxines, and boron halides, as well as adducts of substituted and unsubstituted boranes - including substituted and unsubstituted aminoboranes and substituted and unsubstituted iminoboranes, substituted and unsubstituted heteroboranes, substituted and unsubstituted polyboranes, substituted and unsubstituted poly-boron-heteroatom compounds, substituted and unsubstituted poly-boron compounds, substituted and unsubstituted organoboron compounds, substituted and unsubstituted organopolyboron compounds, substituted and unsubstituted borazines, substituted and unsubstituted boroxines, and boron halides.
  • the at least one borophene is not particularly restricted.
  • the at least one boron-heteroatom-domain comprising a 2D boron network is not particularly restricted.
  • it can be a 2D network mainly formed by individually interlinked boron atoms that contains heteroatoms interspersed, alone or in clusters, and the heteroatoms are not particularly restricted.
  • more than one boron-heteroatom-domain can be included, e.g. with different heteroatom concentration and/or different heteroatoms.
  • the boron-heteroatom-domain comprising a 2D boron network can still comprise defects.
  • the bonding between any of the atoms in the layer can be classical single or multiple 2 electron 2 center bonds; nonclassical electron deficient bonds, nonclassical electron deficient multi center bonds, interacting by either donating electron density to the substrate and/or
  • the boron-containing clusters comprising B-B bonds may also comprise boron-heteroatom and/or even heteroatom-heteroatom bonds if heteroatoms are contained, and the heteroatoms are not particularly restricted and can be e.g. H, halogen, O, S, P, N, C, metals, etc. Also, the boron-containing clusters comprising B-B bonds do not necessarily have to have a regular structure like a tetrahedron, octahedron, icosahedron, but can also have irregular forms, e.g. be skewed, with or without heteroatoms.
  • the clusters for example, boron-containing tetrahedrons, octahedrons, and/or icosahedrons can be interconnected by boron-boron bonds or boron- heteroatoms with each other and thus form a 2D-network.
  • the structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B- heteroatom bonds are connected by B-B bonds is not particularly restricted, as long as the boron heteroatom clusters only have B-heteroatom bonds and the individual clusters are connected by B-B bonds.
  • the borophene and/or boron-heteroatom-domain comprising a 2D boron network may also contain therein different structures comprising boron, e.g. boron-containing clusters comprising B-B bonds and/or boron-containing clusters having B-heteroatom bonds, e.g. regular stoichiometric 2D networks like B2O3 or hexagonal boron nitride (h BN). Also, e.g. heteroatoms may be bonded at fringes of the borophene, etc.
  • borophene one or more boron-heteroatom-domains, a structure of a 2D-network containing a multitude of boron- containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, and/or a structure of a 2D-network containing a multitude of boron- heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron- heteroatom clusters having B-heteroatom bonds are connected by B-B bonds, are produced together, e.g. boron icosahedrons within a borophene layer, boron-heteroatom-domains within borophene, etc.
  • the at least one precursor is diluted in a further gas or gas mixtures that can be reactive and/or inert gases and which are not particularly restricted.
  • a further gas or gas mixtures that can be reactive and/or inert gases and which are not particularly restricted.
  • heteroatoms may be added by e.g. co-dosing of other gases.
  • the contacting of at least one surface of a substrate with at least one precursor in the gaseous or otherwise atomic-molecular excited state is not particularly restricted, and the at least one precursor in the gaseous or otherwise atomic-molecular excited state can e.g. be in a gaseous state, a plasma phase, or other state where atoms and/or molecules are present separately, i.e. without intermolecular interaction.
  • the at least one precursor is in a gaseous state, i.e. a precursor gas, as this is easier to obtain from a suitable source, e.g. a source comprising borazine and/or diborane.
  • the precursor in a gaseous or otherwise atomic-molecular excited state is diluted with other compounds in a gaseous or otherwise excited state, e.g. with gases, e.g. inert gases like hydrogen, nitrogen, etc.
  • gases e.g. inert gases like hydrogen, nitrogen, etc.
  • the at least one precursor in the gaseous or otherwise atomic-molecular excited state comprises at least one precursor, chosen from the group of substituted and unsubstituted boranes - including substituted and unsubstituted aminoboranes and substituted and unsubstituted iminoboranes, substituted and unsubstituted heteroboranes, substituted and unsubstituted polyboranes, substituted and unsubstituted poly-boron-heteroatom compounds - e.g. with a boron number of 2 or more, e.g. 2 - 20, substituted poly-boron compounds - e.g. with a boron number of 2 or more, e.g. 2-20, e.g.
  • polyboron halides substituted and unsubstituted organoboron compounds, e.g. boron aryls, substituted and unsubstituted organopolyboron compounds, e.g. polyboron aryls, substituted and unsubstituted borazines, substituted and unsubstituted boroxines, and boron halides, particularly fluorides, chlorides, bromides and/or iodides, as well as adducts of substituted and unsubstituted boranes - including substituted and unsubstituted aminoboranes and substituted and unsubstituted iminoboranes, substituted and unsubstituted heteroboranes, substituted and unsubstituted polyboranes, substituted and unsubstituted poly-boron- heteroatom compounds, substituted and unsubstituted poly-boron compounds, substituted and unsubstituted organoboron compounds, substituted and un
  • mixtures of these compounds can be comprised in the at least one precursor in the gaseous or otherwise atomic-molecular excited state.
  • the compounds are readily available commercially or as by-products in technically produced compounds, e.g. borazine, where usually e.g. boranes are present as side products, e.g. during synthesis, and/or decomposition products. From such commercially available sources like technical borazine the at least one precursor then can be suitably isolated, e.g. by separation in a cooling trap, e.g. in a vacuum, evaporation, etc., or separately added, etc.
  • Suitable substituents include e.g. azido, amino, nitro, halogen (particularly F, Cl, Br, I), and/or hydroxy groups, particularly amino groups, e.g.
  • aminodiborane like in aminodiborane (B2H7N).
  • aminodiborane m-aminodiborane, B2H5NH2
  • polymer aminoboranes ((NH2BH2) n )
  • borane adducts of polymer aminoboranes e.g. NBB-(NH2-BH2)2-N H2) also borane (BH3) and/or diborane (B2H6) can be liberated.
  • the substituted and unsubstituted organoboron compounds are not particularly restricted and can comprise 1 or more boron atoms and one or more organic residues, like e.g. RBH2, R2B, R3B, etc.
  • Suitable organoboron compound include e.g. BCI3, B2CI4, B4CI4.
  • Suitable borane adducts include e.g. BH3-XTHF, adducts of BCI3, B2CI4, B4CI4, B5H9, B10H14, etc., B2H7N-THF adduct etc.
  • Especially suitable precursors are diborane, which can be e.g.
  • evaporation of BbO, B13N2 can lead to borophene, and substituted borophenes.
  • the at least one precursor is chosen from the group of substituted and unsubstituted boranes, particularly boranes and substituted boranes from which boranes can be easily liberated, like aminodiborane, preferably boranes with 1 to 20 boron atoms, more preferably boranes with 2 to 10 boron atoms, e.g. diborane (B2H6), tetraborane (B4H10), pentaborane (B5H9), decaborane (B10H14), and particularly preferably diborane.
  • the at least one precursor in the gaseous or otherwise atomic-molecular excited state comprises diborane.
  • diborane Particularly with diborane a good and strong film can be easily produced on the at least one surface of the substrate.
  • a suitable precursor is diborane, which is not particularly restricted.
  • diborane is a far better controllable, defined and easily adjustable boron source compared to the evaporation of elemental boron, where elemental boron leads to a manifold of uncontrollable clusters in the gas phase.
  • one or more further gases is present, e.g. an inert and/or otherwise reactive gas, like nitrogen, a noble gas like neon, argon, etc., hydrogen, etc., and/or mixtures thereof, e.g. with an amount of 0 to 99.999999999 Vol.%, e.g. 0 to 99.99999999 Vol.%, e.g. 0 to 99.9999999 Vol.%, e.g. 0 to 99.999999 Vol.%, e.g.
  • the at least one precursor in a gaseous or otherwise atomic-molecular excited state comprises diborane in a range of from 0.000000001 to 100 Vol.%, e.g. 0.00000001 to 100 Vol.%, e.g.
  • 0.0000001 to 100 Vol.% e.g. 0.000001 to 100 Vol.%, e.g. 0.00001 to 100 Vol.%, e.g. 0.0001 to 100 Vol.%, e.g. 0.001 to 100 Vol.%, e.g. 0.01 to 100 vol.%, preferably from 0.1 to 30 vol.%, e.g. in mixtures with other gases.
  • the structure can also be generated on or in other substrates, etc. or on or in mixed substrates.
  • Other phases besides the above structures can be in general of any material, either already present, co-deposited, and/or deposited thereafter.
  • the other substrates and mixed substrates are not particularly restricted and can e.g. encompass metals, alloys, insulators, semiconductors, oxides, nitrides, phosphides, selenides, tellurides, all of them being either single crystalline, multicrystalline, having individual facets or not, having 2D or 3D structures, being of any type of 2D material, or being a combination thereof.
  • the present method it is sufficient to contact only one surface of a substrate, but it is not excluded that more than one surface, e.g. the upper and side surfaces, of the substrates are being contacted, or any three-dimensional structure. It is also included that only distinct crystallographic facets are contacted as one surface, or that these are contacted together with other surface areas. According to certain embodiments distinct crystallographic facets are at least contacted.
  • the substrate is not particularly restricted. It can be a bulk substrate or a layered substrate, etc., and any substrate, e.g. a solid or a molten substrate or a substrate with a molten surface, can be used onto which the at least one precursor can be deposited.
  • the substrate is chosen from a metal substrate - including alloys, a semiconductor substrate, or an insulator, which are not particularly restricted, including non-metallic substrates like graphene, carbides, nitrides like boron nitride, silicon nitride, and/or gallium nitride, phosphides, oxide compounds which are not particularly restricted, or mixtures thereof.
  • Substrates can also be processed semiconductors.
  • Suitable substrates are commercially available, e.g. as wafers.
  • a preferable substrate is a metal substrate, and any metal can be used as the substrate, e.g. late transition metals like Cu, Ag, Au, Pt, Ir, etc., as well as a silicon-based mutlilayer substrates.
  • the at least one surface of the substrate has essentially a homogeneous crystal structure.
  • the at least one surface of the substrate can have a specific surface termination, like 111 faceted, or otherwise faceted, or can be reconstructed or unreconstructed.
  • Suitable substrates include e.g.
  • the at least one surface comprises or is a (111) surface, like I r( 111 ) and/or Cu(111).
  • rotational domains with preferential orientation e.g. dictated by the substrate symmetry, can be formed, but they can also be randomly oriented.
  • the structures can have an epitaxial relation to the substrate, and/or they can be superstructured. Structures, e.g. layers, formed by the deposition can be supported by metals, semiconductors and/or insulators, e.g.
  • domains and layers of borophene and lateral and vertical structures based on building blocks of borophene and heteroatom-substituted borophene are produced by the present method as well. For example, it is also not excluded to produce lateral interfaces of at least one borophene with h BN, e.g. using borazine as a source and activating/deactivating a cold trap for trapping borazine or not.
  • superstructures can be produced that may vary due to the substrate and preparation conditions, as well as the crystallographic orientation of the substrate, e.g. distorted epitaxial growth, etc., but also multiple superstructures might occur within one sample.
  • the purity of the substrate as well as the substrate surface termination are not particularly restricted.
  • the deposition of a structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D- network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron- containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B- B bonds, on the at least one surface of the substrate is not particularly restricted.
  • the at least one precursor can be guided to at least one surface of the substrate, e.g. using a nozzle.
  • a nozzle e.g., a nozzle
  • other methods for depositing are not excluded.
  • the deposition can be carried out using a precursor that is already present on the surface that is then "activated" and thus the final structure is generated.
  • the deposition can be directed in a way that the at least one substrate can be fully covered. However, it is not excluded that an uncomplete or co-doped, e.g. by ubiquitous impurities, boron lattice is formed.
  • the 2D-network can also be formed, e.g. by suitable contacting with a dopant gas, so that it is regularly or irregularly doped with heteroelements, and/or to produce heterostructures, e.g. lateral heterostructures.
  • the dopant gas is not particularly restricted and can e.g. comprise further boron-containing compounds like borazine, organometallic compounds, metal halides, silanes, phosphorus-containing compounds, transition metal compounds, hydrocarbons, etc.
  • lateral and/or vertical heterostructures can be formed, e.g. with other heterostructures that can comprise boron, e.g. with boron nitride, e.g. h BN, and/or with heterostructures that do not comprise boron, like phosphorene, silicene, graphene, 2D transition metal dichalcogenides (TMDs), etc., wherein the further heterostructures are not restricted and can comprise structures in layers, i.e. with a 2D structure, and/or with 3D structure.
  • TMDs transition metal dichalcogenides
  • the shape of the deposited material is not particularly restricted, and can be any shape, e.g. in the form of stripes, dots, circles, squares, etc.
  • other domains can be formed next and/or on top to the deposited at least one borophene, and/or the at least one boron-heteroatom-domain comprising a 2D boron network, and/or the structure of a 2D- network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron- containing cluster comprises 3 to 20 boron atoms, and/or the structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude
  • the structure comprising at least one borophene and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D- network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron- containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B- B bonds, or even the at least one borophene and/or at least one boron-heteroatom
  • the alignment can be induced in preferential orientation depending e.g. on the substrate's electronic and geometric structure, which can lead to a pre-alignment of nuclei on specific crystallographic substrate patterns/surfaces/epitaxial relations, by preferential bonding of nuclei, e.g. boron, to specific substrate atoms, and/or by the growth mode of the structure itself, e.g. due to its intrinsic symmetry, as is e.g. the case of borophene.
  • This will allow a tuning of the domains, orientations etc., as well as the growth of an oriented, confined pattern, e.g. stripes of varying width in atomic scale, islands of specific shape, etc., of a secondary phase, which makes the method particularly adaptable for nanoscale device development.
  • the substrate has a temperature in the range of -196 °C to 3000 °C.
  • the temperature of the substrate is in the range of 0 °C to 1600 °C, e.g. 22 °C to 1500°C, particularly in the range of 500 °C to 1000 °C.
  • the substrate is pre-heated or activated by other means of energy input, allowing a relatively homogeneous formation of a film thereon. It is also not excluded that a chamber, a reactor, etc., in which the production is carried out is pre-heated, e.g. to the same temperature.
  • a heating device used for heating, etc. is therein not particularly restricted.
  • the pressure of the at least one precursor in the gaseous or otherwise atomic-molecular excited state is in the range of 10 10 mbar to 10 bar.
  • it can be in a range from 10 4 to 10 9 mbar, or in a range from 10 4 mbar to 10 bar.
  • the pressure of the at least one precursor in the gaseous or otherwise atomic- molecular excited state is in the range of 10 9 mbar to 10 4 mbar, optionally in the range of 10 8 mbar to 10 7 mbar.
  • a higher vacuum a more homogeneous film can be produced with lower density of defects.
  • Particularly lower pressures are preferable, but also at high pressure and /or in diluted atmosphere a 2D formation may occur.
  • the at least one precursor in the gaseous or otherwise atomic-molecular excited state is dosed onto the at least one surface of the substrate. Dosing enables a good control of crystal growth. The dosing is not particularly restricted and can be carried out using suitable dosing methods.
  • the at least one precursor in the gaseous or otherwise atomic-molecular excited state further comprises a dopant and/or a further boron containing compound like molecular compounds containing B-H, B-O, B-N, B-C, B-Hal (halogen), B-P, and/or B-S bonds, etc., or mixtures thereof, for example borazine, wherein heterostructures of boron and at least one further atom can be formed, e.g. in addition to the structure containing at least one borophene. These can be formed in lateral and/or vertical arrangement.
  • the dopant is not particularly restricted, and dopant elements can be any elements, e.g. N, O, or mixtures thereof, also with other elements.
  • transition metal atoms can be used to increase the storage capacity of some molecules, like h , and/or can be also applied for magnetic functionalization.
  • Chalcogenide atoms may be used to suitably set band gaps so that the structure containing at least one borophene, and/or at least one boron- heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron- containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom
  • Alkali atoms may be added also e.g. for electrical application, e.g. for use of the present structure as electrode material, e.g. anode material, for ion-based batteries.
  • electrode material e.g. anode material
  • organic materials e.g. small organic molecules, like porphyrines or phthalocyanines, is possible for sensing applications.
  • Exemplary suitable methods for implementing the present method include chemical vapor deposition (CVD), including techniques like plasma enhanced CVD and MOCVD (metal organic CVD) as well as similar techniques like atomic layer deposition (ALD), spincoating of the at least one precursor or another method of depositing the precursor, all of them not being particularly restricted, and then producing the structure by bringing it into a gaseous and/or otherwise atomic-molecular excited state, even on the substrate, for contacting in this state, etc.
  • Spincoating and other deposition methods of solid and/or liquid precursors can be carried out using suitable precursors, e.g. also in solution, in a step of contacting according the present method.
  • Solid and/or liquid precursors are preferably leading to a monolayer, and further excess material can e.g. be suitably evaporated, etc.
  • solid precursors also a sublimation is possible.
  • decaborane (B- IO H M ) heteroclosoboranes like SeBnHn and/or carboranes, but also compounds like phenyl dichloroborane, can be dissolved in an organic solute and be spincoated, followed by heating and evaporation, thus being an alternative to contacting e.g. triphenyl borane from the gas or otherwise molecularly excited state, e.g. in a plasma.
  • the structure then can be generated e.g. by thermal annealing upon spincoating.
  • CVD chemical vapor deposition
  • Chemical vapor deposition is a deposition method in controlled atmosphere, and according to certain embodiments also under vacuum, wherein at least one surface of a substrate or the whole substrate is exposed to one or more precursors in the gas phase, particularly one or more volatile precursors.
  • the at least one or more precursors then can react and/or decompose on the at least one substrate surface to produce a desired deposit.
  • volatile by-products are also produced, which can be suitably removed, e.g. by a gas flow through a reaction chamber.
  • the present method it is not excluded to remove the structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or the structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron- containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or the structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B- heteroatom bonds are connected by B-B bonds, from the substrate by a suitable method, and a step of removing the structure containing
  • a layer will remain on the substrate and be used in connection with the substrate.
  • the structure is produced substrate stabilized, and there can be considerable electronic and/or electronic interaction between the substrate, e.g. a metal, and the structure, e.g. a borophene layer, which in itself would then show valuable properties.
  • the substrate e.g. a metal
  • the structure e.g. a borophene layer
  • the structure containing at least one borophene and/or at least one boron- heteroatom-domain comprising a 2D boron network and/or the structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron- containing cluster comprises 3 to 20 boron atoms, and/or the structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B- B bonds, can be combined with suitable other structures which are not restricted, like boron- heteroatom layers with only boron-heter
  • h BN other structures like graphene, perylene 3,4,9, 10-tetracarboxylic dianhydride (PTCDA), transition metal dichalcogenides (TMDs), e.g. TMD monolayers, like M0S2, WS2, MoSe2, WSe2, MoTe2, etc., thus opening up further applications, e.g. in the area of nanoscale devices.
  • PTCDA 10-tetracarboxylic dianhydride
  • TMDs transition metal dichalcogenides
  • TMD monolayers like M0S2, WS2, MoSe2, WSe2, MoTe2, etc.
  • Figure 1 shows a schematic of a borophene single-structure grown by CVD on a substrate, here a metallic support. According to certain embodiments also further layers are produced below and/or on the structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron- heteroatom
  • borazine, a metal, etc., before and/or after contacting it with the at least one precursor in the gaseous or otherwise atomic-molecular excited state comprising at least one precursor, chosen from the group of substituted and unsubstituted boranes, substituted and unsubstituted heteroboranes - including substituted and unsubstituted aminoboranes and substituted and unsubstituted iminoboranes, substituted and unsubstituted polyboranes, substituted and unsubstituted poly-boron-heteroatom compounds, substituted poly-boron compounds, substituted and unsubstituted organoboron compounds, substituted and unsubstituted organopolyboron compounds, substituted and unsubstituted borazines, substituted and unsubstituted boroxines, and boron halides, as well as adducts of substituted and unsubstituted boranes - including substituted and unsubstitute
  • heterostructures with e.g. multiple layers can be formed on the substrate.
  • a monolayer of a hexagonal boron nitride which is grown on top of any borophene layer or borophene submonolayer structure as described previously, produced from e.g. borazine, a structure of sub monolayer domains of borophenes, lateral heterostructures of borophenes and other 2 D materials like h BN, graphene, etc., e.g. lateral heterostructures of borophenes and h BN, or overgrown heterostructures, e.g. of borophenes and h BN, can be formed, where the domain size can correspond to a sub monolayer coverage or a full monolayer coverage.
  • Fig. 2 This is shown schematically in Fig. 2, wherein left top to bottom lateral heterostructures are shown, and right top to bottom vertical heterostructures are shown, e.g. here of borophene type domains or layers (black) and h BN domains or layers (white).
  • a product comprising a structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B- B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20, e.g.
  • certain aspects thereof will be applicable based on the description of the present method, so that these aspects also apply to the present product.
  • the product can also be coupled to a substrate, as mentioned above.
  • the product can comprise multiple layers, of which at least one is a layer comprising a structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B- heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-
  • the further layer or layers are not restricted and can be below and/or above the structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B- B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B-B bonds. Also different domains and/or structures can be
  • At least one layer is contained below and/or on the structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron- heteroatom clusters having B-heteroatom bonds are connected by B-B bonds, which can be the same or different, also as discussed above,
  • a monolayer of a hexagonal boron nitride which is grown on top of any borophene layer or a borophene submonolayer structure as described previously.
  • lateral heterostructures with other 2D materials like h BN, graphene, etc. e.g. lateral heterostructures of borophenes and h BN, or overgrown heterostructures, e.g. of borophenes and h BN.
  • further layers e.g. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more, can be included in the product, which are not particularly restricted, like boron- heteroatom layers with only boron-heteroatom bonds, e.g.
  • BN e.g. h BN, other structures like graphene, perylene 3,4,9, 10-tetracarboxylic dianhydride (PTCDA), transition metal dichalcogenides (TMDs), e.g. TMD monolayers, like M0S2, WS2, MoSe2, WSe2, MoTe2, etc.
  • PTCDA 10-tetracarboxylic dianhydride
  • TMDs transition metal dichalcogenides
  • TMD monolayers like M0S2, WS2, MoSe2, WSe2, MoTe2, etc.
  • At least one borophene and/or at least one boron- heteroatom-domain comprising a 2D boron network is present as a monoatomic layer on the surface of the substrate.
  • STM/STS data were acquired by a CreaTec STM operating at 6K under ultra-high vacuum conditions (P ⁇ 2 c 10 10 mbar). STM images were taken at constant current mode and treated using the WSxM software.
  • borazine B 3 H 6 N 3 available from a commercial supplier (Katchem) and borazine prepared according to literature methods, it was observed that both materials do contain considerable amounts of additional volatile boron species. These originate from the decompositon of amine-borane H3N-BH3, and m-aminodiborane B2H5NH2, which are both intermediates occurring during the borazine synthesis and are in itself sources of borane BH 3 , and diborane B 2 H 6 , also leading to higher and thermally instable aminoboranes (Nh Bhy n , and borane adducts of polymer amineboranes HsB-(NH2-BH2) n - NH 2 , and from the borane and diborane formation, side reactions to higher boranes may occur.
  • Diborane can lead in separate side reactions to the formation of higher boranes, such as e.g. pentaborane B 5 H 9 , which is stable enough and not too volatile to be released fully into the gas phase, so it also could be detected as an intermediate in the NMR spectra. Also hydrolysis and oxidation due to mandatory technological processing, solvent purities, refilling, handling, etc., volatile hydrido-oxo-mino compounds of variable stoichiometry may occur leading to the formation of non-volatile polymer boron compounds and borane/diborane in the borazine.
  • boranes such as e.g. pentaborane B 5 H 9 , which is stable enough and not too volatile to be released fully into the gas phase, so it also could be detected as an intermediate in the NMR spectra.
  • hydrolysis and oxidation due to mandatory technological processing, solvent purities, refilling, handling, etc. volatile hydrido-oxo-mino compounds of variable
  • Borazine handling and preparation was made by Schlenk-techniques under Argon; ⁇ B-NMR measurements were made with a Bruker ACP 200 spectrometer in molten NMR tubes with separately sealed lock capillaries (CeDe) inside.
  • a borophene film has been grown on atomically pure lr(111) and Cu(111) substrates using the setup shown in Figure 3.
  • the lr(111) single crystal was prepared by repeated cycles of sputtering (Ar+ ions at an energy of 1 keV) and annealing (resistive heating at 1000°C).
  • the Cu(111) single crystal was prepared by repeated cycles of sputtering (Ar+ ions at an energy of 1 keV) and annealing (resistive heating at 760°C for Cu(111)).
  • a precursor gas container 1 technical borazine comprising additives leading to diborane was provided, which was then led through a cold trap 2 to separate the diborane from other volatile species, which was then led as precursor gas 3 onto the respective substrate 6 in the growth chamber 4 under controlled pressure and temperature, a pumping system 5 providing for a suitable pressure.
  • Diborane gas (B2H6) was therein confirmed as a compound occurring in commercially available borazine (B3H6N3), being e.g.
  • Fig. 4 therein shows a comparison between borophene grown by the exemplary CVD method applied with those by the current PVD (physical vapor deposition)
  • Inset High-resolution STM image showing the borophene appearance identified previously in literature (Vinogradov, N. A., Lyalin, A., Taketsugu, T., Vinogradov, A. S., & Preobrajenski, A. (2019).
  • White protrusions observed on top of the borophene layer in the STM spectra correspond to physisorbed 3D clusters, as indicated by the ease of displacing them with the STM tip and the lack of additional boron bonds observed in the XPS B 1s. They could be originated by trace contaminants present in the UHV chamber, such as N 3 ⁇ 4 O2 or H2O.
  • Complementary XPS chemical characterization of the polymorph grown by CVD confirmed the absence of nitrogen and presence of boron in the 2D sheet.
  • the B 1s core-level signal consists of a symmetric peak that can be well-reproduced by a Voigt-like function centered at 188.7 ⁇ 0.1 eV binding energy, thus being shifted by 1 - 1.6 eV with respect to other borophenes on Ag(111) and Cu(111) in the state of the art.
  • the shift is consistent with the reduction of adsorption distance on I r( 111 ) (2.1 A) compared to Ag (111) (2.4 A) and Cu(111) (2.3 A), and points towards a stronger borophene-substrate interaction for lr(111), reminiscent of the trend observed for other 2D materials.
  • the full width at half maximum of 1.3 eV (larger than the energy resolution of the apparatus ⁇ 1 eV) of the B 1s peak suggests a multiple-peak sub-structure. This could be explained by the large variations of charge density within this borophene sheet on lr(111) and/or the presence of diverse B bonding schemes with heteroatoms residually present, e.g. from the precursor or the synthesis chamber.
  • CVD-grown borophene on Cu(111) exhibits domains with a periodic structure defined by a rhomboidal unit cell.
  • the evaluation of the fast Fourier transforms (FFT) calculated for independent borophene domains reveals that these prefer to grow forming two mirror- symmetric structures, each one rotated by 5.0 ⁇ 1.5°.
  • these mirror-symmetric domains can also grow along three different orientations rotated by 120°, thus forming a 3- fold alignment of pairs of mirror-symmetric domains with the (111) surface. This result corroborates the (V73xV39)R ⁇ 5.8° on Cu(111) superstructure reported before, hence endorsing the identification of our borophene polymorph as c3— like polymorph.
  • boron clusters e.g. derived from tetrahedrons, octahedrons and/or icosahedrons, either isolated or connected, also could be observed, which is also to be expected from the extremely variable bonding chemistry of boron.
  • heteroatoms could be included in such clusters. Such clusters might account to a broadening in the lower binding region in XPS spectra observed.
  • Example 2 Production of lateral interfaces of a borophene with hexagonal boron nitride A film was produced as in Example 1, except that at certain points in time the cold trap 2 was deactivated, resulting in lateral interfaces of borophene with hexagonal boron nitride (h BN). Again, large borophene domains on fully covered lr(111) exceeding lateral sizes reported previously by more than one order of magnitude were obtained, with atomically precise lateral interfaces to h BN.
  • the precursors for borophene and h BN were selectively dosed by activating and deactivating the cold trap, as they coexist in the same precursor gas.
  • 0.03 L of borazine were dosed onto lr(111) kept at 1233 K in a first step, followed by 2.7 L of diborane in a second step.
  • the dose of borazine corresponds to that of sub-monolayer growth of h BN, therefore allowing enough free catalytic surface for the following borophene synthesis.
  • the resulting 2D layer reveals coexisting domains of borophene and h BN that fully cover the lr(111) surface, hence forming lateral heterostructures.
  • FIG. 5 An exemplary lateral heterostructure of the produced borophene and h BN with a sharp interface is shown in Fig. 5, a structure that is not feasible to obtain by other methods.
  • the STM image in Fig. 5(a) therein shows a higher magnification than the one in Fig. 5(b), clearly showing the sharp border between the two structures.
  • Borophene domains feature the three orientations and the stripy appearance with zigzag motifs discussed above, while h BN domains also preserve the characteristic appearance reported for pristine /iBN/lr(111).
  • the latter represents a single 12-on-11 moire superstructure with a periodicity of 2.89 nm, consequence of the small lattice mismatch and locked orientation along the high symmetry directions of the surface h BN zigzag edges (and the corresponding h BN symmetry axis) are oriented in parallel to the borophene stripes, which both are aligned to one of the three high-symmetry axis of lr(111).
  • borophene edges parallel to the stripes are energetically preferred, as indicated by their prevalence in borophene islands and edges to h BN. This promotes the formation of straight heterojunctions oriented in three equivalent directions with fixed lateral stacking.
  • the borophene-related density of states extends to the very interface with h BN.
  • the spectroscopical features are better visualized in the single dl/dV spectrum, where a minimum of intensity is observed around 0.7 V. While the line-shape compares reasonably well with those measured for borophenes c3 and b12 on Ag(111) and c6 on Cu(111), as produced above, the position of the minima is shifted considerably towards higher voltage. This observation is consistent with the depopulation of states near EF as compared to the cases of borophene on Ag and Cu, consistent to the charge transfer from such substrates occurring in the opposite direction (0.08e to lr(111), in contrast to 0.03 and 0.23e from Ag(111) and Cu(111) respectively).
  • h BN presents an electronic structure with lower density of states at EF, that it is spatially modulated along the moire pattern as a consequence of the registry-dependent hybridization of N with Ir atoms (36).
  • Fig. 2C the crossing between dl/dV spectra corresponding to h BN "pore" and “wire” regions is consistent with the STM contrast inversion observed at different bias voltages, likewise the crossing between h BN and borophene dl/dV curves at ⁇ 1.5 V accounts for the contrast inversion between both 2D layers.
  • Borophene-ZiBN lateral heterostructures grown on lr(111) by CVD were further characterized using extended STM and STS (scanning tunneling spectroscopy) characterization.
  • Large-area STM images evidence that borophene domains preserve the three orientations reflecting the symmetry of the underlying (111) surface upon formation of lateral heterostructures with h BN.
  • h BN domains appear oriented in three possible degenerated orientations, in which its moire superstructure is aligned along the three possible alignments of the c6 borophene stripes (i.e. along the high symmetry axis of lr(111 )).
  • Borophene domains presented elongated shapes in the direction of its zigzag ("wavy") stripes, thus indicating that the borophene facets parallel to the stripes are energetically preferred upon lateral bonding with h BN, and that borophene crystallizes at higher temperatures than h BN during the cooling process h BN domains appear mostly truncated along the high-symmetry axis of its moire superstructure, which indicates that they preferably bond with borophene via zigzag- terminated edges. This is observed in atomically-resolved STM images. A series of dl/dV spectra around the Fermi level taken across the borophene-ZiBN interface show that the electronic transition takes place without apparent formation of interfacial states. The anisotropic growth morphology of borophene domains furthermore enabled atomically precise alignment and contacting of other subsequently grown phases like it is shown for hm. Relevance of the invention
  • this system allows to easily grow large scale borophenes, it particularly shows the typical advantages of a process from the gaseous or otherwise atomic-molecular excited phase, particularly in a CVD process over other growth processes.
  • a particularly important advantage is to be seen in the use of diborane gas, particularly high purity diborane gas.
  • the present findings open new perspectives for the synthesis of borophene-type compounds, with direct impact in semiconductors, flexible/stretchable electronics, wear resistant/tribology, hard materials/interfaces, magnetic applications, biomedical applications, etc. e.g. with metal, semimetal or nonmetal interfaces, involving e.g.
  • nanotribology electronic, photonic and/or spintronic aspects of quantum confinement and/or further atomic-level properties, e.g. tribology, in particular for nano- and micromechanical devices, particularly in the fabrication of (semi-)conducting films for e.g. nanoscale electronic devices and applications, e.g. for energy conversion and storage systems, as e.g. disclosed in "Disclosing boron's thinnest side” (Sachdev, H. (2015). Disclosing boron's thinnest side. Science, 350(6267), 1468-1469.
  • particularly tough films comprising borophenes, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D- network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron- containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B- B bonds, can be produced on a larger scale.

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Abstract

The invention relates to a method for the production of a structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron- containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B- heteroatom bonds are connected by B-B bonds, as well as a product comprising a structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B-B bonds.

Description

Borophene synthesis
The invention relates to a method for the production of a structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron- containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B- heteroatom bonds are connected by B-B bonds, as well as a product comprising a structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron- heteroatom clusters having B-heteroatom bonds are connected by B-B bonds. Also disclosed are products derived by lateral and or vertical combination of any type of the above with other 2D Materials described subsequently.
Technological field
Since the isolation of atomically thin graphene from layered graphite in 2004, a collection of two-dimensional (2D) materials have been derived from their 3D layered counterparts. They exhibit unique physical properties arising from the reduction in dimensionality, which make them highly attractive for fundamental research and for technological applications in electronics, photonics, energy conversion and storage, and biomedicine. Entirely synthetic 2D materials expand the -otherwise limited- library of 2D materials beyond those not owing a layered analogue, and open a new perspective for engineered properties based on pre designed composition and in-plane atomic structure. Recent progress in the synthesis methods has allowed the experimental realization of various examples, such as silicene, germanene or bismuthene, making them available for fundamental research and exploitation of their novel properties.
Borophenes, which comprise in their definition according to the state of the art usually atomically thin sheets formed by boron, are a prominent member of the family of synthetic 2D materials due to their anisotropic and polymorphic structures and superlative strength and stiffness compared to graphene, as disclosed in Mannix, A. J., Zhang, Z., Guisinger, N. P., Yakobson, B. I., & Hersam, M. C. (2018). Borophene is a prototype for synthetic 2D materials development, as described in Nature Nanotechnology, 13(6), 444^150. https://doi.org/10.1038/s41565-018-0157-4. Borophenes can be considered to be of single atomic thickness, but can also be thought to be extended to structures of 2D aspect ratio due to interconnected cluster subunits, still being different from and not resembling known 3D polymorphs of elemental boron. The large diversity of stable structures that borophenes can adopt, consequence of the variable geometry of the B multi-centre bonding configurations, provide a great opportunity for advanced property engineering, as discussed in Sachdev, H. (2015). Disclosing boron's thinnest side. Science, 350(6267), 1468-1469. https://doi.org/10.1126/science.aad7021. For instance, conventional phonon-mediated superconductivity has been predicted for a number of polymorphs, as well as anisotropic metallicity and optical transparency, anisotropic bending and stretching flexibility, or high capacity for hydrogen and ion storage. Nevertheless, the measurement of many of these fundamental properties and attributes remain still elusive due to the poor quality of the samples synthesized to date.
Prior state of the art To date, the method used for the synthesis of borophenes is generally based on a physical vapor deposition (PVD) approach, consisting on directing a beam of material previously sublimated from elemental solid sources onto a pre-heated substrate. It was successfully employed to grow a borophene in 2015 for the first time, as described by Mannix, A. J., Zhou, X.-F., Kiraly, B., Wood, J. D., Alducin, D., Myers, B. D., Guisinger, N. P. (2015). Synthesis of borophenes: Anisotropic, two-dimensional boron polymorphs. Science, 350(6267), 1513- 1516. https://doi.org/10.1126/science.aad1080, and Feng, B., Zhang, J., Zhong, Q., Li, W., Li, S., Li, H., Wu, K. (2016). Experimental realization of two-dimensional boron sheets. Nature Chemistry, 8(6), 563-568. https://doi.org/10.1038/nchem.2491, using a high purity B solid source and an Ag (111) surface as substrate, and thereafter replicated on a still limited number of substrates, Ag(110), Au(111), Al(111) and lr(111). A typical issue encountered is the small size of domains and the coexistence of different polymorphs in the same sample or even domain, as e.g. shown in Fig. 4b (Feng, B. et al., Nature Chemistry, 2016), and no control of the growth species. The lack of extended, i.e. at least micrometer-sized, single-crystalline domains and poor control over polymorph selectivity as well as selectively tuning the growth parameters limits the measurement of its fundamental properties under intrinsic conditions, i.e. without lateral confinement effects, as well as bans the growth on or transfer to other supports for further explorations or applications. The limitations of the current PVD methods aim to a reconsideration of the growth approach.
Chemical vapor deposition (CVD) by using specific precursors has shown to be a flexible and scalable growth method, suitable to produce large single 2D crystals, and nowadays is widely used for the synthesis of numerous 2D materials, as e.g. discussed by Cai, Z., Liu, B., Zou, X., & Cheng, H.-M. (2018). Chemical Vapor Deposition Growth and Applications of Two- Dimensional Materials and Their Heterostructures [Review-article] Chemical Reviews, 118(13), 6091-6133. https://doi.org/10.1021/acs.chemrev.7b00536). Its working principle is usually based on the decomposition of a precursor gas on a, generally pre-heated, substrate, in which the selection of gas and substrate, pressure and temperature are key parameters to tune the properties of the resulting material. Attempts using CVD to grow boron nanostructures yielded amorphous structures, nanotubes and thick planar structures, as e.g. described by Tian, J., Xu, Z., Shen, C, Liu, F., Xu, N., & Gao, H.-J. (2010). One-dimensional boron nanostructures: Prediction, synthesis, characterizations, and applications. Nanoscale, 2(8), 1375, https://doi.org/10.1039/c0nr00051e, and Tai, G., Hu, T., Zhou, Y., Wang, X., Kong, J., Zeng, T., ... Wang, Q. (2015). Synthesis of Atomically Thin Boron Films on Copper Foils. Angewandte Chemie International Edition, 54(51), 15473-15477. https://doi.org/10.1002/anie.201509285, but none of them produced single-atom-thick B layers. The main reason that explain the current failure is that adequate precursors are yet to be found, and the lack of well-controlled and clean growth conditions. There thus remains a need for a controlled synthesis of structures containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron- containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B- heteroatom bonds are connected by B-B bonds, particularly in at least pm scale.
Brief description of the invention
The present inventors found a reliable and more effective method of producing borophenes, and/or boron-heteroatom-domains comprising 2D boron networks, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B- B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron- containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B- B bonds, which enables production of the structures in increased size and high homogeneity and lower density of defects. The structures therein do not resemble known 3D polymorphs of elemental boron, but refer to 2D polymorphs, polymorphs with pronounced 2D aspect ratio and their derivates and products. These borophene based structures do also differ from amorphous boron monolayers which in principle might be feasible by CVD, due to their intrinsic 2D structural ordering. In a first aspect the present invention relates to a method for the production of a structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron- heteroatom clusters having B-heteroatom bonds are connected by B-B bonds, the method comprising: contacting at least one surface of a substrate with at least one precursor in a gaseous or otherwise atomic-molecular (i.e. atomic and/or molecular) excited state, wherein the substrate has a temperature in the range of -196 °C to 3000 °C, and deposition of a structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D- network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron- containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B- B bonds, on the at least one surface of the substrate, wherein a pressure of the at least one precursor in the gaseous or otherwise atomic- molecular excited state is in the range of 10 10 mbar to 10 bar, and wherein the at least one precursor in the gaseous or otherwise atomic-molecular excited state comprises at least one precursor, chosen from the group of substituted and unsubstituted boranes - including substituted and unsubstituted aminoboranes and substituted and unsubstituted iminoboranes, substituted and unsubstituted heteroboranes, substituted and unsubstituted polyboranes, substituted and unsubstituted poly-boron- heteroatom compounds, substituted poly-boron compounds, substituted and unsubstituted organoboron compounds, substituted and unsubstituted organopolyboron compounds, substituted and unsubstituted borazines, substituted and unsubstituted boroxines, and boron halides, as well as adducts of substituted and unsubstituted boranes - including substituted and unsubstituted aminoboranes and substituted and unsubstituted iminoboranes, substituted and unsubstituted heteroboranes, substituted and unsubstituted polyboranes, substituted and unsubstituted poly-boron-heteroatom compounds, substituted and unsubstituted poly-boron compounds, substituted and unsubstituted organoboron compounds, substituted and unsubstituted organopolyboron compounds, substituted and unsubstituted borazines, substituted and unsubstituted boroxines, and boron halides.
While in general all boron-containing precursors can be used to create boron films or boron layers, these films or layers created can be amorphous or crystalline and have a 3D connectivity of boron atoms derived from known 3D polytypes of elemental boron. However, these films or layers do not reveal structures resembling a structure as disclosed herein and obtainable by the present method, resembling pronounced polymorphs with a particular 2D aspect ratio.
Further disclosed is a product comprising a structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B- B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B-B bonds, particularly produced by the present method, wherein the structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron- heteroatom clusters having B-heteroatom bonds are connected by B-B bonds, comprises at least one homologous domain with a size of at least 100 nm by 100 nm, preferably micrometer-sized (i.e. 1 pm by 1 pm or larger) single-crystalline domains, or even larger.
Further aspects and embodiments of the invention are disclosed in the dependent claims and can be taken from the following description, figures and examples, without being limited thereto.
Figures
The enclosed drawings should illustrate embodiments of the present invention and convey a further understanding thereof. In connection with the description they serve as explanation of concepts and principles of the invention. Other embodiments and many of the stated advantages can be derived in relation to the drawings. The elements of the drawings are not necessarily to scale towards each other. Identical, functionally equivalent and acting equal features and components are denoted in the figures of the drawings with the same reference numbers, unless noted otherwise.
Fig. 1 shows schematically growth of a borophene using chemical vapor deposition.
Fig. 2 shows schematically possible heterolayer and/or multilayer products that can be produced by the present method.
In Fig. 3 an exemplary experimental, labscale setup used for producing exemplary products in the present Examples is schematically shown. Fig. 4 depicts images of products obtained in the present examples (Fig. 4 a) and of comparative examples produced in the state of the art (Figs. 4b and 4c according to the above Feng et al., 2016, Nature Chemistry, and the above Mannix et al., 2015 Science).
Fig. 5 shows STM images of a borophene - h BN lateral heterostructure produced according to the invention.
Detailed description of the present invention
Definitions
Unless defined otherwise, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
Clusters can formally be considered as molecular building blocks for forming the present structures, but can also be seen as entities being part of the structures, either 2D or 3D.
As the present nomenclature regarding borophenes in the literature is extremely heterogeneous due to a manifold of theoretical models and still based on very few experimental results, and due to the complexity of boron systems, the following definitions apply with regard to borophenes and further compounds.
With regard to the different boron containing structures, it is to be understood that the term "containing" can mean that the different atoms, molecules, groups, etc. are formally contained, but are not necessarily to be seen as separate entities as they can be and normally are of the respective network, etc. This particularly applies to clusters within a network, as they are only formally contained but are not isolated and rather form a part of the network.
Within the scope of the present invention, the boron in the different compounds can have any isotope ratio, e.g. be isotopically pure for 10B or 11 B, have the naturally occurring atomic ratio of 10B to 11B of approximately 20:80, or any other ratio. Due to individual nuclear spin properties (l=3 for 10B, 3/2 for 11B) as well as high neutron capture properties for 10B, and due to the availability of isotope-enriched boron precursors, e.g. boranes, of various grades, all aspects of formation of the structures disclosed herein, e.g. borophene formation, are deemed to be valid to any boron isotope ratio, since they can be provided by the precursor, and even isotopically pure domains and heterodomains are feasible. Thus, the present structures also may be applicable to applications where specific properties of the different isotopes are required, e.g. for neutron detection, etc.
Borophenes are - single or multiple - layers of regular or defective networks of boron atoms which may be corrugated, i.e. slightly shifted in directions out of the 2D plane in each layer. They are based on structural motifs of boron sheets of single atomic thickness, i.e. form a sort of sheet that can be regarded as quasi two-dimensional. Particularly, layers of borophenes do not have to be atomically "flat", i.e. do not only extend in two dimensions, but still may be described as 2D due to their B-B bonds only being within the layer. Borophenes also can be derived from an array of 2 dimensionally interlinked boron clusters (e.g. edge on or side on interconnects, leading to a 2D sheet type structures of high aspect ratio thus resembling different structure than the classical 3D polymorphs of boron, with electrostatic or van der Waals type intersheet interactions or covalent interactions of bond orders lower than 1 due to the nonclassical bonding of boron. While it is considered that borophenes do not form boron-boron covalent bonds between different layers, i.e. out of the layer, this does not exclude that interactions occur between two distinct layers of borophene, e.g. van der Waals type or other interactions weaker than the B-B interactions within the borophene 2D layer. Borophenes comprise a manifold of crystal structures that can form in sheets in different forms, and e.g. intrinsically corrugated, symmetry-reduced - with regular defect positions as well as intrinsically buckling patterns - structures may result from a "two dimensional" boron network, which even can be further modulated by the substrate symmetry. Also planar or partly planar networks are not excluded. Further, borophenes can also form different polymorphs, which are included as well. Borophenes comprise B-B-bonds of variable strength, and may even consist of mainly B-B-bonds of variable strength, and may or may not have additional electronic interactions with a substrate and/or adatoms, dopants, covering layers, etc., which also can be incorporated into a borophene network, e.g. at crystallographic defects, be attached on the rim, derive from the substrate, and/or be placed on top, but are not part of the borophene. If the heteroatoms form a part of the borophene lattice the structure herein is as defined for boron-heteroatom-domains comprising a 2D boron network. It is not excluded that borophenes comprise multiple layers that are e.g. arranged on top of each other, similar to graphene heterostructures. Boron-boron bonds do not only comprise classical covalent bonds within the 2D layer structure, but can also comprise different kinds of bonds, e.g. non-classical multi-center bonds and e.g. allow interaction with a substrate and/or adatoms, dopants, covering layers, etc. Theoretical studies have shown the existence of different borophene polymorphs, a consequence of the multi-center bonding configuration of boron that can lead to e.g. structures based on triangular arrays of boron atoms with variable density and periodic distribution of single-B vacancies. Thus, it is also possible that there can be stronger interactions between different layers comprising boron atoms, which can be suitably deposited by the present method. There can be bonds of bond order below 1 between layers, with an electron density between layers smaller than in a B-B covalent single bond. In this regard, it is also not excluded that other interactions like ionic and/or electrostatic interactions exist between layers.
Boron-heteroatom-domains comprising a 2D boron network are herein defined structures which contain within the 2D boron network one or more species of heteroatoms on substitutional and/or additional sites and/or do contain heteroatoms strongly linked on the surface, and/or also can have heteroatoms like O or N at the rim or incorporated in the 2D lattice. Like in the case of borophene, the 2D boron network is sheet-like in a layer but does not have to be flat. It can be a regular or defective network comprising boron atoms with boron boron bonds. It is of single atomic thickness, and may be corrugated, i.e. slightly shifted in directions out of the 2D plane and does not form boron-boron bonds out of the layer, i.e. form a sort of sheet that can be regarded as quasi two-dimensional. It encompasses doped borophenes wherein heteroatoms - which are not restricted - are incorporated into the boron-boron lattice as well as also lattices comprising boron-boron bonds wherein heteroatoms are introduced e.g. by residual compounds, impurities, the substrate, etc. Thus, boron-heteroatom domains comprising a 2D boron network also encompass borophene- based networks with a variable content of heteroatoms like oxygen, nitrogen, carbon and/or hydrogen, stemming e.g. from impurities and/or residues in the production process, as well as borophene-based networks where doping with heteroatoms is intentionally carried out.
One heteroatom or multiple heteroatoms can be included which can be the same or different, i.e. the content thereof is variable. Possible heteroatoms include e.g. nitrogen, hydrogen, oxygen, carbon, halogens, metals, etc., and/or mixtures thereof. The boron- heteroatom-domains comprising a 2D boron network thus include borophene-derived layers with variable content of heteroatoms, as well as borophenes doped with heteroatoms, i.e. wherein the heteroatom is purposely introduced. For example, even boron-heteroatom- domains comprising a 2D boron network with large amounts of heteroatoms are included, as long as boron boron bonds are contained, e.g. leading to structures like BxOa, BxNt>, BXHC, BxCd, wherein the x:a ratio is not reaching an B:0 atomic ratio of 1:1,5 (B2O3), the x:b ratio is not reaching a B:N atomic ratio of 1:1 (BN), the x:c ratio is not reaching a B:H atomic ratio of 1:3 (BH3, B2H6), and the x:d ratio is not reaching a B:C atomic ratio of 1:4 (B4C). Similar considerations are possible accordingly for other heteroatoms. Accordingly, also borophenes where heteroatoms are bonded in the lattice, at the rim, etc. in the layer are considered to be boron-heteroatom-domains comprising a 2D boron network.
Particularly, the boron-heteroatom-domains comprising a 2D boron network can still be rich in boron with respect to the layer stoichiometry, i.e. contain boron with respect to the boron heteroatom domain with 50 at% or more, e.g. more than 50 at%., preferably more than 60 at.%, more preferably more than 70 at%. However, also higher amounts of heteroatoms are not excluded.
In particular, regular stoichiometric 2D networks like B2O3 or BN are excluded. The heteroatoms in boron-heteroatom-domains are not particularly restricted, and in principle any heteroatom of the periodic system of the elements can be incorporated into a boron- heteroatom domain, and also mixtures of heteroatoms. In a preferred boron-heteroatom domain preferred heteroatoms are chosen from the group consisting of H, D, O, N, C, P, S, Se, and/or Te, particularly H, D, O, N, C, P and/or S. Also, further groups and/or heteroatoms may be attached to heteroatoms, e.g. N, C, P, that may have further possible bonding sites, and such heteroatoms and/or groups are not restricted and can e.g. include hydrogen, D, halogens, amines, alcoholates, organyls, aryls, etc.
A structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom - but do not all or some have to comprise a heteroatom, wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds is not particularly restricted. As is clear, the boron- containing clusters comprising B-B bonds can comprise at least one heteroatom and/or can also comprise no heteroatom, so that structures with only boron-containing clusters comprising B-B bonds with only boron atoms in the clusters are encompassed, structures wherein all boron-containing clusters comprising B-B bonds comprise at least one heteroatom, and structures where at least one or some boron-containing clusters comprising B-B bonds comprise heteroatoms, and at least one or some boron-containing clusters comprising B-B bonds comprise no heteroatoms. The term "structure of a 2D-network" with regard to the structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds is therein meant in the sense that the structure forms a layer that extends in two dimensions, e.g. the x and y plane, although also regular or irregular extensions in the further dimension, e.g. the z plane, will occur due to the clusters, but the clusters themselves are again connected within the sheet, thus leading to a 2D network of high aspect ratio. In contrast to the borophene or the boron-heteroatom-domains comprising a 2D boron network, which form a layer direct on a surface, the structure of a 2D- network containing a multitude of boron-containing clusters comprising B-B bonds forms a layer that also covers a surface, but the bonds within the network do not have to be in direct vicinity of the surface, as different boron-containing clusters can be connected next to the surface, or in a different plane above a surface between different boron containing clusters, e.g. through tips of boron-containing icosahedrons, etc. Thus, the structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds also forms a network that is sheet-like in a layer, but is not flat due to clusters contained therein. As in the two cases above, it can be a regular or defective network comprising boron atoms in clusters with boron boron bonds. It is not of single atomic thickness due to the clusters, but at places can have single atomic thickness, e.g. between clusters or at positions where clusters are bonded. It, like the other structures, can even have vacancies if a structural unit is missing, as also described for borophene. The structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds is at least corrugated at clusters, i.e. slightly shifted in directions out of the 2D plane, but can also be corrugated at other places, e.g. between clusters. The structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds can thus also be seen as quasi two-dimensional, with peaks protruding e.g. at positions of clusters. The clusters are not particularly restricted and can be built form at least 3 atoms, e.g. at least 4 atoms, but also more atoms, like 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more. For example, boron clusters of (B2), B3, B4, B5, Bb, Bg, ..., units can be considered to be formally derived from cluster compounds such as (B2H6), B3H7, B4H10, B5H9, ....B10H14, ... However, while such a formal description of the structure, formally built from clusters like (boron or boron-containing) icosahedral structures like e.g .alpha rhombohedral boron in the 3D case, can be considered, in the real formation of the structure of a 2D-network containing a multitude of boron-containing clusters comprising B- B bonds from cluster compounds having e.g. icosahedral building blocks or tetrahedral building blocks like B4CI4, other compounds, e.g. even gas phase species being formed by evaporation or decay of boranes, may interfere, so that the structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds does not have to be regular but can have any form. Also clusters comprising B-B bonds containing heteroatoms, like e.g. derived from an insertion of molecules like SeBnHn, etc., can be formed, and thus lead to changes in the structure, etc.
Formally, at certain locations within the network or also according to certain embodiments, the structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds can also be considered to be derived from a multitude of boron- containing clusters that are connected. While it is not excluded that the structure of a 2D- network containing a multitude of boron-containing clusters comprising B-B bonds comprises only boron atoms, it is also not excluded that one heteroatom or more heteroatoms is contained, that are not restricted and can be the same as in the boron- heteroatom-domain comprising a 2D-network. In the structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds the cluster cannot be isolated, as they are connected, but they are present in a step before formation of the layer. In the structure of a 2D-network containing a multitude of boron-containing clusters comprising B- B bonds the bonds between clusters are not particularly restricted and can be connected by B-B bonds or B-heteroatom bonds, depending on the location where clusters are bonded, and B-heteroatom bonds between clusters can e.g. be formed if at least one cluster contains at least one heteroatom.
Also, the structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B- heteroatom bonds are connected by B-B bonds, is not restricted. As in the case of the structure of a 2D-network containing a multitude of boron-containing clusters comprising B- B bonds defined above, also in the structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds the term "structure of a 2D-network" is therein meant in the sense that the structure forms a layer that extends in two dimensions, e.g. the x and y plane, although also regular or irregular extensions in the further dimension, e.g. the z plane, will occur due to the clusters, but the clusters themselves are again connected within the sheet. Also, all other considerations with regard to the structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds defined above apply to the structure of a 2D-network containing a multitude of boron- heteroatom clusters having B-heteroatom bonds, with the sole difference that in the clusters no B-B bonds are present but B-heteroatoms only, and the clusters are connected by B-B bonds between two B-atoms of the clusters or also more B atoms in between, e.g. in a sheet like in borophene or the boron-heteroatom-domain comprising a 2D boron network with B-B bonds in the 2D boron network, the clusters being bonded to such a network with B-B bonds at least somewhere, preferably in direct vicinity to the cluster. Also, the same considerations apply to the clusters and the heteroatoms in the structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds as apply to the structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, i.e. will also particularly have a defined 2D aspect ratio, as defined above for other structures.
In the present method as well as in the present product it is not excluded that, apart from the at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron- containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron- heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron- heteroatom clusters having B-heteroatom bonds are connected by B-B bonds, further heterostructures that do or do not contain boron, like boron-heteroatom 2D-networks, other sheet-like materials, 3D-materials, are contained, e.g. in layered (vertical) and/or adjacent (horizontal) proximity, as will be also discussed in more detail later, and such structures are also encompassed in the present method and product.
Amounts within the present invention are given in wt.%, unless not stated otherwise or clear from context.
Before the invention is described in exemplary detail, it is to be understood that this invention is not limited to the particular component parts of the process steps of the methods described herein as such methods may vary. It is also to be understood that the terminology used herein is for purposes of describing particular embodiments only, and is not intended to be limiting. It must be noted that, as used in the specification and the appended claims, the singular forms "a," "an" and "the" include singular and/or plural referents unless the context clearly dictates otherwise. For example, the term "a" as used herein can be understood as one single entity or in the meaning of "one or more" entities. It is also to be understood that plural forms include singular and/or plural referents unless the context clearly dictates otherwise. It is moreover to be understood that, in case parameter ranges are given which are delimited by numeric values, the ranges are deemed to include these limitation values.
In a first aspect the present invention relates to a method for the production of a structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20, e.g. 4 to 20, boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B-B bonds, comprising: contacting at least one surface of a substrate with at least one precursor in a gaseous or otherwise atomic-molecular excited state, wherein the substrate has a temperature in the range of -196 °C to 3000 °C, and deposition of a structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D- network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron- containing cluster comprises 3 to 20. e.g. 4 to 20, boron atoms, and/or a structure of a 2D- network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B-B bonds, on the at least one surface of the substrate, wherein a pressure of the at least one precursor in the gaseous or otherwise atomic- molecular excited state is in the range of 10 10 mbar to 10 bar, and wherein the at least one precursor in the gaseous or otherwise atomic-molecular excited state comprises at least one precursor, chosen from the group of substituted and unsubstituted boranes - including substituted and unsubstituted aminoboranes and substituted and unsubstituted iminoboranes, substituted and unsubstituted heteroboranes, substituted and unsubstituted polyboranes, substituted and unsubstituted poly-boron- heteroatom compounds, e.g. carboranes or azaboranes, substituted poly-boron compounds, e.g. polyboron halides, substituted and unsubstituted organoboron compounds, e.g. boron aryls, substituted and unsubstituted organopolyboron compounds, e.g. polyboron aryls, substituted and unsubstituted borazines, substituted and unsubstituted boroxines, and boron halides, as well as adducts of substituted and unsubstituted boranes - including substituted and unsubstituted aminoboranes and substituted and unsubstituted iminoboranes, substituted and unsubstituted heteroboranes, substituted and unsubstituted polyboranes, substituted and unsubstituted poly-boron-heteroatom compounds, substituted and unsubstituted poly-boron compounds, substituted and unsubstituted organoboron compounds, substituted and unsubstituted organopolyboron compounds, substituted and unsubstituted borazines, substituted and unsubstituted boroxines, and boron halides.
In the present invention the at least one borophene is not particularly restricted. Also the at least one boron-heteroatom-domain comprising a 2D boron network is not particularly restricted. For example it can be a 2D network mainly formed by individually interlinked boron atoms that contains heteroatoms interspersed, alone or in clusters, and the heteroatoms are not particularly restricted. Also more than one boron-heteroatom-domain can be included, e.g. with different heteroatom concentration and/or different heteroatoms. Also the boron-heteroatom-domain comprising a 2D boron network can still comprise defects.
In the borophene layer or the layer of the at least one boron-heteroatom-domain comprising a 2D boron network, the structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, and/or the structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B-B bonds, the bonding between any of the atoms in the layer can be classical single or multiple 2 electron 2 center bonds; nonclassical electron deficient bonds, nonclassical electron deficient multi center bonds, interacting by either donating electron density to the substrate and/or accepting electron density from the substrate and/or adatoms, etc., if present. Furthermore, it is not excluded that electrostatic, van der Waals and/or ionic interactions may occur within the layers, between the layer and the substrate and/or the layer and adatoms, etc., if present. Furthermore, the structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B- heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, is also not particularly restricted. The boron-containing clusters comprising B-B bonds may also comprise boron-heteroatom and/or even heteroatom-heteroatom bonds if heteroatoms are contained, and the heteroatoms are not particularly restricted and can be e.g. H, halogen, O, S, P, N, C, metals, etc. Also, the boron-containing clusters comprising B-B bonds do not necessarily have to have a regular structure like a tetrahedron, octahedron, icosahedron, but can also have irregular forms, e.g. be skewed, with or without heteroatoms. In the structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, the clusters, for example, boron-containing tetrahedrons, octahedrons, and/or icosahedrons can be interconnected by boron-boron bonds or boron- heteroatoms with each other and thus form a 2D-network.
Also the structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B- heteroatom bonds are connected by B-B bonds, is not particularly restricted, as long as the boron heteroatom clusters only have B-heteroatom bonds and the individual clusters are connected by B-B bonds.
In the structure produced by the present method, and the method as well, also different structures may be included, e.g. the borophene and/or boron-heteroatom-domain comprising a 2D boron network may also contain therein different structures comprising boron, e.g. boron-containing clusters comprising B-B bonds and/or boron-containing clusters having B-heteroatom bonds, e.g. regular stoichiometric 2D networks like B2O3 or hexagonal boron nitride (h BN). Also, e.g. heteroatoms may be bonded at fringes of the borophene, etc. In the present invention it is also not excluded that borophene, one or more boron-heteroatom-domains, a structure of a 2D-network containing a multitude of boron- containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, and/or a structure of a 2D-network containing a multitude of boron- heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron- heteroatom clusters having B-heteroatom bonds are connected by B-B bonds, are produced together, e.g. boron icosahedrons within a borophene layer, boron-heteroatom-domains within borophene, etc.
Within the present method, it is not excluded to contact the substrate with a different precursor before and/or after contacting it with the at least one precursor in a gaseous or otherwise atomic-molecular excited state comprising at least one precursor, chosen from the group of substituted and unsubstituted boranes - including substituted and unsubstituted aminoboranes and substituted and unsubstituted iminoboranes, substituted and unsubstituted heterobora nes, substituted and unsubstituted polyboranes, substituted and unsubstituted poly-boron-heteroatom compounds, substituted poly-boron compounds, substituted and unsubstituted organoboron compounds, substituted and unsubstituted organopolyboron compounds, substituted and unsubstituted borazines, substituted and unsubstituted boroxines, and boron halides, as well as adducts of substituted and unsubstituted boranes - including substituted and unsubstituted aminoboranes and substituted and unsubstituted iminoboranes, substituted and unsubstituted heteroboranes, substituted and unsubstituted polyboranes, substituted and unsubstituted poly-boron- heteroatom compounds, substituted and unsubstituted poly-boron compounds, substituted and unsubstituted organoboron compounds, substituted and unsubstituted organopolyboron compounds, substituted and unsubstituted borazines, substituted and unsubstituted boroxines, and boron halides, and deposit different materials, or even at the same time at the same time at the same or a different location. This way, multi-layered structures and/or heterostructures with different domains in one layer, e.g. borophene next to h BN, can be prepared. Also, it is not excluded that the at least one precursor is diluted in a further gas or gas mixtures that can be reactive and/or inert gases and which are not particularly restricted. This way, heteroatoms may be added by e.g. co-dosing of other gases.
In the present method, the contacting of at least one surface of a substrate with at least one precursor in the gaseous or otherwise atomic-molecular excited state is not particularly restricted, and the at least one precursor in the gaseous or otherwise atomic-molecular excited state can e.g. be in a gaseous state, a plasma phase, or other state where atoms and/or molecules are present separately, i.e. without intermolecular interaction. According to preferred embodiments the at least one precursor is in a gaseous state, i.e. a precursor gas, as this is easier to obtain from a suitable source, e.g. a source comprising borazine and/or diborane. In the present invention it is not excluded that the precursor in a gaseous or otherwise atomic-molecular excited state is diluted with other compounds in a gaseous or otherwise excited state, e.g. with gases, e.g. inert gases like hydrogen, nitrogen, etc. The at least one precursor in the gaseous or otherwise atomic-molecular excited state comprises at least one precursor, chosen from the group of substituted and unsubstituted boranes - including substituted and unsubstituted aminoboranes and substituted and unsubstituted iminoboranes, substituted and unsubstituted heteroboranes, substituted and unsubstituted polyboranes, substituted and unsubstituted poly-boron-heteroatom compounds - e.g. with a boron number of 2 or more, e.g. 2 - 20, substituted poly-boron compounds - e.g. with a boron number of 2 or more, e.g. 2-20, e.g. polyboron halides, substituted and unsubstituted organoboron compounds, e.g. boron aryls, substituted and unsubstituted organopolyboron compounds, e.g. polyboron aryls, substituted and unsubstituted borazines, substituted and unsubstituted boroxines, and boron halides, particularly fluorides, chlorides, bromides and/or iodides, as well as adducts of substituted and unsubstituted boranes - including substituted and unsubstituted aminoboranes and substituted and unsubstituted iminoboranes, substituted and unsubstituted heteroboranes, substituted and unsubstituted polyboranes, substituted and unsubstituted poly-boron- heteroatom compounds, substituted and unsubstituted poly-boron compounds, substituted and unsubstituted organoboron compounds, substituted and unsubstituted organopolyboron compounds, substituted and unsubstituted borazines, substituted and unsubstituted boroxines, and boron halides. Also mixtures of these compounds can be comprised in the at least one precursor in the gaseous or otherwise atomic-molecular excited state. The compounds are readily available commercially or as by-products in technically produced compounds, e.g. borazine, where usually e.g. boranes are present as side products, e.g. during synthesis, and/or decomposition products. From such commercially available sources like technical borazine the at least one precursor then can be suitably isolated, e.g. by separation in a cooling trap, e.g. in a vacuum, evaporation, etc., or separately added, etc. Substitutes and heteroatoms in the substituted or unsubstituted boranes, substituted and unsubstituted heterobora nes, substituted and unsubstituted polyboranes, substituted or unsubstituted poly-boron-heteroatom compounds, substituted and unsubstituted organoboron compounds, substituted and unsubstituted organopolyboron compounds, and substituted poly-boron compounds, as well as in the adducts, are not particularly restricted. Suitable substituents include e.g. azido, amino, nitro, halogen (particularly F, Cl, Br, I), and/or hydroxy groups, particularly amino groups, e.g. like in aminodiborane (B2H7N). From e.g. aminodiborane (m-aminodiborane, B2H5NH2), polymer aminoboranes ((NH2BH2)n) and borane adducts of polymer aminoboranes (e.g. NBB-(NH2-BH2)2-N H2) also borane (BH3) and/or diborane (B2H6) can be liberated. The substituted and unsubstituted organoboron compounds are not particularly restricted and can comprise 1 or more boron atoms and one or more organic residues, like e.g. RBH2, R2B, R3B, etc. with various organic residues R that can be the same or different, and/or can e.g. comprise 1 to 100 C atoms, tributyborane being an example of a suitable organoboron compound. Suitable boron halides include e.g. BCI3, B2CI4, B4CI4. Suitable borane adducts include e.g. BH3-XTHF, adducts of BCI3, B2CI4, B4CI4, B5H9, B10H14, etc., B2H7N-THF adduct etc. Especially suitable precursors are diborane, which can be e.g. supplied as a gas diluted in an inert gas like Ar, N¾ H2, borane adducts like BH3-THF, etc., boron trichloride, B2CI4, B4CI4 , organoboron compounds leading to borane, e.g. under dehydroboration reactions, substituted diborane compounds with substituents like aryl, alkyl, halogen, e.g. Me2N-B(CI)-B(CI)-NMe2, and boranes like diborane B2H6, pentaborane B5H9, decaborane B10H14; Furthermore, boron suboxides BxO, x=1-6, e.g. B2O, B2O2, BbO, and boron subnitrides ByN, y= 1.01 -7, e.g. B13N2, can also be used as precursors when brought into the gas phase e.g. by evaporation or any other means of energy input. For example, evaporation of BbO, B13N2 can lead to borophene, and substituted borophenes.
According to certain embodiments the at least one precursor is chosen from the group of substituted and unsubstituted boranes, particularly boranes and substituted boranes from which boranes can be easily liberated, like aminodiborane, preferably boranes with 1 to 20 boron atoms, more preferably boranes with 2 to 10 boron atoms, e.g. diborane (B2H6), tetraborane (B4H10), pentaborane (B5H9), decaborane (B10H14), and particularly preferably diborane. According to certain embodiments the at least one precursor in the gaseous or otherwise atomic-molecular excited state comprises diborane. Particularly with diborane a good and strong film can be easily produced on the at least one surface of the substrate. The present inventors particularly found that a suitable precursor is diborane, which is not particularly restricted. Particularly diborane is a far better controllable, defined and easily adjustable boron source compared to the evaporation of elemental boron, where elemental boron leads to a manifold of uncontrollable clusters in the gas phase.
It is not excluded that during the contacting the at least one surface of the substrate with the at least one precursor in a gaseous or otherwise atomic-molecular excited state, and/or during the deposition of the structure, one or more further gases is present, e.g. an inert and/or otherwise reactive gas, like nitrogen, a noble gas like neon, argon, etc., hydrogen, etc., and/or mixtures thereof, e.g. with an amount of 0 to 99.999999999 Vol.%, e.g. 0 to 99.99999999 Vol.%, e.g. 0 to 99.9999999 Vol.%, e.g. 0 to 99.999999 Vol.%, e.g. 0 to 99.99999 Vol.%, e.g. 0 to 99.9999 Vol.%, e.g. 0 to 99.999 Vol.%, e.g. 0 to 99.99 Vol.% e.g. 0 to 99.9 Vol.%, e.g. 0.1 to 99 Vol.%, e.g. 20 to 95 Vol.%, e.g. 95 Vol.%, e.g. a mixture of diborane 5% in hydrogen, etc. According to certain embodiments the at least one precursor in a gaseous or otherwise atomic-molecular excited state comprises diborane in a range of from 0.000000001 to 100 Vol.%, e.g. 0.00000001 to 100 Vol.%, e.g. 0.0000001 to 100 Vol.%, e.g. 0.000001 to 100 Vol.%, e.g. 0.00001 to 100 Vol.%, e.g. 0.0001 to 100 Vol.%, e.g. 0.001 to 100 Vol.%, e.g. 0.01 to 100 vol.%, preferably from 0.1 to 30 vol.%, e.g. in mixtures with other gases.
By comprising further gases and/or mixtures of precursors the structure can also be generated on or in other substrates, etc. or on or in mixed substrates. Other phases besides the above structures can be in general of any material, either already present, co-deposited, and/or deposited thereafter. The other substrates and mixed substrates are not particularly restricted and can e.g. encompass metals, alloys, insulators, semiconductors, oxides, nitrides, phosphides, selenides, tellurides, all of them being either single crystalline, multicrystalline, having individual facets or not, having 2D or 3D structures, being of any type of 2D material, or being a combination thereof.
In the present method it is sufficient to contact only one surface of a substrate, but it is not excluded that more than one surface, e.g. the upper and side surfaces, of the substrates are being contacted, or any three-dimensional structure. It is also included that only distinct crystallographic facets are contacted as one surface, or that these are contacted together with other surface areas. According to certain embodiments distinct crystallographic facets are at least contacted.
In the present method the substrate is not particularly restricted. It can be a bulk substrate or a layered substrate, etc., and any substrate, e.g. a solid or a molten substrate or a substrate with a molten surface, can be used onto which the at least one precursor can be deposited. According to certain embodiments the substrate is chosen from a metal substrate - including alloys, a semiconductor substrate, or an insulator, which are not particularly restricted, including non-metallic substrates like graphene, carbides, nitrides like boron nitride, silicon nitride, and/or gallium nitride, phosphides, oxide compounds which are not particularly restricted, or mixtures thereof. Substrates can also be processed semiconductors. Suitable substrates are commercially available, e.g. as wafers. A preferable substrate is a metal substrate, and any metal can be used as the substrate, e.g. late transition metals like Cu, Ag, Au, Pt, Ir, etc., as well as a silicon-based mutlilayer substrates. According to certain embodiments the at least one surface of the substrate has essentially a homogeneous crystal structure. Particularly the at least one surface of the substrate can have a specific surface termination, like 111 faceted, or otherwise faceted, or can be reconstructed or unreconstructed. Suitable substrates include e.g. Si(111), Si(100), Ge, SiC, GaN, lr(111), Cu(111), Ag(111), Ag(110), Al(111), Au(111), etc. According to certain embodiments, the at least one surface comprises or is a (111) surface, like I r( 111 ) and/or Cu(111). Depending on the substrate, rotational domains with preferential orientation, e.g. dictated by the substrate symmetry, can be formed, but they can also be randomly oriented. For example, the structures can have an epitaxial relation to the substrate, and/or they can be superstructured. Structures, e.g. layers, formed by the deposition can be supported by metals, semiconductors and/or insulators, e.g. due to the interaction of the structures with the substrate in view of e.g. bonding characteristics in the structure. Due to these characteristics also lateral or vertical heterostructures containing borophenes and other 2D materials and/or organic compounds can be produced, as well as also multi-layer structures. According to certain embodiments, domains and layers of borophene and lateral and vertical structures based on building blocks of borophene and heteroatom-substituted borophene are produced by the present method as well. For example, it is also not excluded to produce lateral interfaces of at least one borophene with h BN, e.g. using borazine as a source and activating/deactivating a cold trap for trapping borazine or not. Depending on the substrate, superstructures can be produced that may vary due to the substrate and preparation conditions, as well as the crystallographic orientation of the substrate, e.g. distorted epitaxial growth, etc., but also multiple superstructures might occur within one sample. The purity of the substrate as well as the substrate surface termination are not particularly restricted.
Also the deposition of a structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D- network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron- containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B- B bonds, on the at least one surface of the substrate is not particularly restricted. For example, the at least one precursor can be guided to at least one surface of the substrate, e.g. using a nozzle. However, also other methods for depositing are not excluded. It is also included that the deposition can be carried out using a precursor that is already present on the surface that is then "activated" and thus the final structure is generated.
With the present method, the at least one borophene and/or at least one boron-heteroatom- domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron- heteroatom clusters having B-heteroatom bonds are connected by B-B bonds, can be deposited in domains of mesoscopic to nanoscopic size as defective or non-defective layers, and can also be formed as doped or undoped layers, as described above and below. The deposition can be directed in a way that the at least one substrate can be fully covered. However, it is not excluded that an uncomplete or co-doped, e.g. by ubiquitous impurities, boron lattice is formed. As stated above or below, the 2D-network can also be formed, e.g. by suitable contacting with a dopant gas, so that it is regularly or irregularly doped with heteroelements, and/or to produce heterostructures, e.g. lateral heterostructures. The dopant gas is not particularly restricted and can e.g. comprise further boron-containing compounds like borazine, organometallic compounds, metal halides, silanes, phosphorus-containing compounds, transition metal compounds, hydrocarbons, etc. This way lateral and/or vertical heterostructures can be formed, e.g. with other heterostructures that can comprise boron, e.g. with boron nitride, e.g. h BN, and/or with heterostructures that do not comprise boron, like phosphorene, silicene, graphene, 2D transition metal dichalcogenides (TMDs), etc., wherein the further heterostructures are not restricted and can comprise structures in layers, i.e. with a 2D structure, and/or with 3D structure. Also, different domains of two or more of borophene, at least one boron-heteroatom-domain comprising a 2D boron network, a structure of a 2D-network containing a multitude of boron-containing clusters comprising B- B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, and a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B-B bonds, on the at least one surface of the substrate, in combination with any of the above lateral and/or heterostructures can be formed, layered vertical structures with two or more of borophene, at least one boron-heteroatom-domain comprising a 2D boron network, a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B- heteroatom bonds, and a structure of a 2D-network containing a multitude of boron- heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron- heteroatom clusters having B-heteroatom bonds are connected by B-B bonds, on the at least one surface of the substrate and at least one of the above heterostructures above, below and/or between them, etc. Of particular interest is that with the present method confined, rigid and conducting boundary lines between different, e.g. insulating, domains can be generated with growth at a nano scale, which is quite unique.
The shape of the deposited material is not particularly restricted, and can be any shape, e.g. in the form of stripes, dots, circles, squares, etc. Also, as described, other domains can be formed next and/or on top to the deposited at least one borophene, and/or the at least one boron-heteroatom-domain comprising a 2D boron network, and/or the structure of a 2D- network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron- containing cluster comprises 3 to 20 boron atoms, and/or the structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B- B bonds, which are not restricted, and can be in any shape, thickness, of any material, etc. With the present method, particularly the present product can be produced. However, it is not excluded that products with a smaller size are produced by the present method.
According to certain aspects, the structure comprising at least one borophene and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D- network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron- containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B- B bonds, or even the at least one borophene and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron- heteroatom clusters having B-heteroatom bonds are connected by B-B bonds, itself, can be deposited pre-oriented, aligned and/or grown of any secondary phase, e.g. depending on substrate surface orientation. The alignment, for example, can be induced in preferential orientation depending e.g. on the substrate's electronic and geometric structure, which can lead to a pre-alignment of nuclei on specific crystallographic substrate patterns/surfaces/epitaxial relations, by preferential bonding of nuclei, e.g. boron, to specific substrate atoms, and/or by the growth mode of the structure itself, e.g. due to its intrinsic symmetry, as is e.g. the case of borophene. This will allow a tuning of the domains, orientations etc., as well as the growth of an oriented, confined pattern, e.g. stripes of varying width in atomic scale, islands of specific shape, etc., of a secondary phase, which makes the method particularly adaptable for nanoscale device development.
In the present method the substrate has a temperature in the range of -196 °C to 3000 °C. According to certain embodiments the temperature of the substrate is in the range of 0 °C to 1600 °C, e.g. 22 °C to 1500°C, particularly in the range of 500 °C to 1000 °C. According to certain embodiments the substrate is pre-heated or activated by other means of energy input, allowing a relatively homogeneous formation of a film thereon. It is also not excluded that a chamber, a reactor, etc., in which the production is carried out is pre-heated, e.g. to the same temperature. A heating device used for heating, etc., is therein not particularly restricted.
In the present method the pressure of the at least one precursor in the gaseous or otherwise atomic-molecular excited state is in the range of 10 10 mbar to 10 bar. For example, it can be in a range from 104 to 109 mbar, or in a range from 104 mbar to 10 bar. According to certain embodiments the pressure of the at least one precursor in the gaseous or otherwise atomic- molecular excited state is in the range of 109 mbar to 104 mbar, optionally in the range of 108 mbar to 107 mbar. With a higher vacuum a more homogeneous film can be produced with lower density of defects. Particularly lower pressures are preferable, but also at high pressure and /or in diluted atmosphere a 2D formation may occur. If the pressure is too low, a growth of borophene islands may occur, which is less preferred. According to certain embodiments a single layer or multiple layers of the structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B-B bonds, is formed on the at least one surface of the substrate. As discussed above, it is thus possible to form heterostructures as superstructures, but also homogeneous structures of several borophene layers can be produced, analogous to graphene. According to certain embodiments the at least one precursor in the gaseous or otherwise atomic-molecular excited state is dosed onto the at least one surface of the substrate. Dosing enables a good control of crystal growth. The dosing is not particularly restricted and can be carried out using suitable dosing methods.
According to certain embodiments the at least one precursor in the gaseous or otherwise atomic-molecular excited state further comprises a dopant and/or a further boron containing compound like molecular compounds containing B-H, B-O, B-N, B-C, B-Hal (halogen), B-P, and/or B-S bonds, etc., or mixtures thereof, for example borazine, wherein heterostructures of boron and at least one further atom can be formed, e.g. in addition to the structure containing at least one borophene. These can be formed in lateral and/or vertical arrangement. The dopant is not particularly restricted, and dopant elements can be any elements, e.g. N, O, or mixtures thereof, also with other elements. Also, other elements can be considered as alternative or additional dopants. For example, transition metal atoms can be used to increase the storage capacity of some molecules, like h , and/or can be also applied for magnetic functionalization. Chalcogenide atoms may be used to suitably set band gaps so that the structure containing at least one borophene, and/or at least one boron- heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron- containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B- B bonds, may also find application in electronic devices, e.g. as transistor. Alkali atoms may be added also e.g. for electrical application, e.g. for use of the present structure as electrode material, e.g. anode material, for ion-based batteries. Also the application of organic materials, e.g. small organic molecules, like porphyrines or phthalocyanines, is possible for sensing applications.
The production of the structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D- network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron- containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B- B bonds, is not particularly restricted if the steps of the present method are followed. Exemplary suitable methods for implementing the present method include chemical vapor deposition (CVD), including techniques like plasma enhanced CVD and MOCVD (metal organic CVD) as well as similar techniques like atomic layer deposition (ALD), spincoating of the at least one precursor or another method of depositing the precursor, all of them not being particularly restricted, and then producing the structure by bringing it into a gaseous and/or otherwise atomic-molecular excited state, even on the substrate, for contacting in this state, etc. Spincoating and other deposition methods of solid and/or liquid precursors can be carried out using suitable precursors, e.g. also in solution, in a step of contacting according the present method. Spincoating and the other deposition methods of solid and/or liquid precursors is preferably leading to a monolayer, and further excess material can e.g. be suitably evaporated, etc. For solid precursors also a sublimation is possible. For example, decaborane (B-IOHM), heteroclosoboranes like SeBnHn and/or carboranes, but also compounds like phenyl dichloroborane, can be dissolved in an organic solute and be spincoated, followed by heating and evaporation, thus being an alternative to contacting e.g. triphenyl borane from the gas or otherwise molecularly excited state, e.g. in a plasma. The structure then can be generated e.g. by thermal annealing upon spincoating.
According to certain embodiments the production of the structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron- containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B- heteroatom bonds are connected by B-B bonds, is carried out using chemical vapor deposition (CVD). Chemical vapor deposition (CVD) is a deposition method in controlled atmosphere, and according to certain embodiments also under vacuum, wherein at least one surface of a substrate or the whole substrate is exposed to one or more precursors in the gas phase, particularly one or more volatile precursors. The at least one or more precursors then can react and/or decompose on the at least one substrate surface to produce a desired deposit. It is also possible that volatile by-products are also produced, which can be suitably removed, e.g. by a gas flow through a reaction chamber.
According to certain embodiments, the production of the structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron- containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B- heteroatom bonds are connected by B-B bonds, is polymorph-selective, i.e. can lead to specific polymorphs of borophene, etc., e.g. depending on the substrate.
In the present method it is not excluded to remove the structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or the structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron- containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or the structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B- heteroatom bonds are connected by B-B bonds, from the substrate by a suitable method, and a step of removing the structure containing at least one borophene and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or the structure of a 2D- network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron- containing cluster comprises 3 to 20 boron atoms, and/or the structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B- B bonds, from the substrate can be included in the present method. However, according to certain embodiments the structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D- network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron- containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B- B bonds, e.g. a layer, will remain on the substrate and be used in connection with the substrate. In general, due to the electronic structure due to non-classical bonding within the structure, e.g. a layer, it may be preferable that the structure is produced substrate stabilized, and there can be considerable electronic and/or electronic interaction between the substrate, e.g. a metal, and the structure, e.g. a borophene layer, which in itself would then show valuable properties. This opens up e.g. possible applications in nanotribology, magnetism and/or spintronic applications. Further, also it is possible this way to combine domains of different hardness, combining e.g. hard and soft domains, giving rise to unique applications as well.
In this regard the structure containing at least one borophene and/or at least one boron- heteroatom-domain comprising a 2D boron network, and/or the structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron- containing cluster comprises 3 to 20 boron atoms, and/or the structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B- B bonds, can be combined with suitable other structures which are not restricted, like boron- heteroatom layers with only boron-heteroatom bonds, e.g. h BN, other structures like graphene, perylene 3,4,9, 10-tetracarboxylic dianhydride (PTCDA), transition metal dichalcogenides (TMDs), e.g. TMD monolayers, like M0S2, WS2, MoSe2, WSe2, MoTe2, etc., thus opening up further applications, e.g. in the area of nanoscale devices.
Figure 1 shows a schematic of a borophene single-structure grown by CVD on a substrate, here a metallic support. According to certain embodiments also further layers are produced below and/or on the structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron- heteroatom clusters having B-heteroatom bonds are connected by B-B bonds, by suitable contacting of and deposition on the at least one surface of the substrate and/or the structure with a further second precursor, e.g. borazine, a metal, etc., before and/or after contacting it with the at least one precursor in the gaseous or otherwise atomic-molecular excited state comprising at least one precursor, chosen from the group of substituted and unsubstituted boranes, substituted and unsubstituted heteroboranes - including substituted and unsubstituted aminoboranes and substituted and unsubstituted iminoboranes, substituted and unsubstituted polyboranes, substituted and unsubstituted poly-boron-heteroatom compounds, substituted poly-boron compounds, substituted and unsubstituted organoboron compounds, substituted and unsubstituted organopolyboron compounds, substituted and unsubstituted borazines, substituted and unsubstituted boroxines, and boron halides, as well as adducts of substituted and unsubstituted boranes - including substituted and unsubstituted aminoboranes and substituted and unsubstituted iminoboranes, substituted and unsubstituted heteroboranes, substituted and unsubstituted polyboranes, substituted and unsubstituted poly-boron-heteroatom compounds, substituted and unsubstituted poly-boron compounds, substituted and unsubstituted organoboron compounds, substituted and unsubstituted organopolyboron compounds, substituted and unsubstituted borazines, substituted and unsubstituted boroxines, and boron halides. This way heterostructures with e.g. multiple layers can be formed on the substrate. For example, a monolayer of a hexagonal boron nitride, which is grown on top of any borophene layer or borophene submonolayer structure as described previously, produced from e.g. borazine, a structure of sub monolayer domains of borophenes, lateral heterostructures of borophenes and other 2 D materials like h BN, graphene, etc., e.g. lateral heterostructures of borophenes and h BN, or overgrown heterostructures, e.g. of borophenes and h BN, can be formed, where the domain size can correspond to a sub monolayer coverage or a full monolayer coverage.
With the present method, it is thus not excluded that also other layers, i.e. one or more, two or more, three or more, four or more, etc., are deposited prior and/or after the structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron- heteroatom clusters having B-heteroatom bonds are connected by B-B bonds, leading to multilayer structures.
This is shown schematically in Fig. 2, wherein left top to bottom lateral heterostructures are shown, and right top to bottom vertical heterostructures are shown, e.g. here of borophene type domains or layers (black) and h BN domains or layers (white).
Further disclosed is a product comprising a structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B- B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20, e.g. 4 to 20, boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B- heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B- heteroatom bonds are connected by B-B bonds, particularly produced by the present method, wherein the structure containing at least one borophene, and/or at least one boron- heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron- containing cluster comprises 3 to 20, e.g. 4 to 20, boron atoms, and/or a structure of a 2D- network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B-B bonds, comprises at least one homologous domain with a size of at least 100 nm by 100 nm, preferably micrometer-sized single-crystalline domains, i.e. with an extension in at least one lateral extension or preferably in two lateral dimensions of the 2D- network of at least one micrometer. As the product is particularly produced by the present method, certain aspects thereof will be applicable based on the description of the present method, so that these aspects also apply to the present product. Thus, the product can also be coupled to a substrate, as mentioned above. Also, as mentioned above, the product can comprise multiple layers, of which at least one is a layer comprising a structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B- heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B-B bonds. The further layer or layers are not restricted and can be below and/or above the structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B- B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B-B bonds. Also different domains and/or structures can be formed next to such structure, as discussed above. In this regard reference is made to possible structures, configurations, layer structures, etc. as mentioned with regard to the present method, and which can be realized in the present product.
According to certain embodiments at least one layer is contained below and/or on the structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron- heteroatom clusters having B-heteroatom bonds are connected by B-B bonds, which can be the same or different, also as discussed above, and is not particularly restricted, and can be e.g. for example, a monolayer of a hexagonal boron nitride, which is grown on top of any borophene layer or a borophene submonolayer structure as described previously. Also encompassed in the product are, lateral heterostructures with other 2D materials like h BN, graphene, etc., e.g. lateral heterostructures of borophenes and h BN, or overgrown heterostructures, e.g. of borophenes and h BN. Also further layers, e.g. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more, can be included in the product, which are not particularly restricted, like boron- heteroatom layers with only boron-heteroatom bonds, e.g. BN, e.g. h BN, other structures like graphene, perylene 3,4,9, 10-tetracarboxylic dianhydride (PTCDA), transition metal dichalcogenides (TMDs), e.g. TMD monolayers, like M0S2, WS2, MoSe2, WSe2, MoTe2, etc.
According to certain embodiments at least one borophene and/or at least one boron- heteroatom-domain comprising a 2D boron network is present as a monoatomic layer on the surface of the substrate. The above embodiments can be combined arbitrarily, if appropriate. Further possible embodiments and implementations of the invention comprise also combinations of features not explicitly mentioned in the foregoing or in the following with regard to the examples of the invention. Particularly, a person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention.
Examples
The present invention will now be described in detail with reference to several examples thereof. However, these examples are illustrative and do not limit the scope of the invention.
Sample characterization
STM/STS data were acquired by a CreaTec STM operating at 6K under ultra-high vacuum conditions (P < 2 c 10 10 mbar). STM images were taken at constant current mode and treated using the WSxM software.
XPS data was taken by a SPECS PHOIBOS 100 hemispherical electron analyzer using the Al Kcc line as monochromatic X-ray source (1253.6 eV), and energy referenced to the Fermi level. Measurements were performed at RT, grazing emission configuration (70°) and P=1 x 109 mbar. Fits to the experimental data were performed using the XPST macro for IGOR (Dr Martin Schmid, Philipps University Marburg), using Voigt-like functions (Gauss-Lorentzian ratio of 0.3). CreaTec STM and SPECS XPS apparatus are mounted in different ultra-high vacuum chambers. Samples were transferred between the CreaTec STM and SPECS XPS ultra-high vacuum chambers using a Ferrovac VSN40S Ultra High Vacuum Suitcase (P= 1 x 109 mbar).
While screening the quality of borazine B3H6N3 available from a commercial supplier (Katchem) and borazine prepared according to literature methods, it was observed that both materials do contain considerable amounts of additional volatile boron species. These originate from the decompositon of amine-borane H3N-BH3, and m-aminodiborane B2H5NH2, which are both intermediates occurring during the borazine synthesis and are in itself sources of borane BH3, and diborane B2H6, also leading to higher and thermally instable aminoboranes (Nh Bhyn, and borane adducts of polymer amineboranes HsB-(NH2-BH2)n- NH2, and from the borane and diborane formation, side reactions to higher boranes may occur. Diborane can lead in separate side reactions to the formation of higher boranes, such as e.g. pentaborane B5H9, which is stable enough and not too volatile to be released fully into the gas phase, so it also could be detected as an intermediate in the NMR spectra. Also hydrolysis and oxidation due to mandatory technological processing, solvent purities, refilling, handling, etc., volatile hydrido-oxo-mino compounds of variable stoichiometry may occur leading to the formation of non-volatile polymer boron compounds and borane/diborane in the borazine.
Borazine handling and preparation was made by Schlenk-techniques under Argon; ^B-NMR measurements were made with a Bruker ACP 200 spectrometer in molten NMR tubes with separately sealed lock capillaries (CeDe) inside.
Example 1: Production of a borophene
A borophene film has been grown on atomically pure lr(111) and Cu(111) substrates using the setup shown in Figure 3. The lr(111) single crystal was prepared by repeated cycles of sputtering (Ar+ ions at an energy of 1 keV) and annealing (resistive heating at 1000°C). The Cu(111) single crystal was prepared by repeated cycles of sputtering (Ar+ ions at an energy of 1 keV) and annealing (resistive heating at 760°C for Cu(111)). In a precursor gas container 1 technical borazine comprising additives leading to diborane was provided, which was then led through a cold trap 2 to separate the diborane from other volatile species, which was then led as precursor gas 3 onto the respective substrate 6 in the growth chamber 4 under controlled pressure and temperature, a pumping system 5 providing for a suitable pressure. Diborane gas (B2H6) was therein confirmed as a compound occurring in commercially available borazine (B3H6N3), being e.g. formed from aminodiborane, polymer aminoboranes (Nh Bh K and borane adducts of polymer aminoboranes like N3B-(NH2-BH2)2-NH2, wherein the presence of at least aminodiborane could be confirmed by in-situ measured mass spectroscopy (data available). Also, the presence of m-aminodiborane was confirmed by screening borazine by ^B-NMR. When dosing the gas precursor, single-crystalline borophenes formed for substrate temperatures from 500°C to 1000°C and pressures from 107 to 108 mbar, exemplary results thereof as shown in Fig. 4a.
Fig. 4 therein shows a comparison between borophene grown by the exemplary CVD method applied with those by the current PVD (physical vapor deposition) (a) STM (scanning tunneling microscopy) image showing part of an extended single-crystalline borophene domain on an lr(111) surface. Inset: High-resolution STM image showing the borophene appearance identified previously in literature (Vinogradov, N. A., Lyalin, A., Taketsugu, T., Vinogradov, A. S., & Preobrajenski, A. (2019). Single-Phase Borophene on lr(111): Formation, Structure, and Decoupling from the Support. ACS Nano, (111), acsnano.9b08296. https://doi.org/10.1021/acsnano.9b08296). (b) - (c) STM images showing small and multi- domain borophene crystals and structures reported by Mannix, A. J., Zhou, X.-F., Kiraly, B., Wood, J. D., Alducin, D., Myers, B. D., ... Guisinger, N. P. (2015). Synthesis of borophenes: Anisotropic, two-dimensional boron polymorphs. Science, 350(6267), 1513-1516. https://doi.org/10.1126/science.aad1080 and Feng, B., Zhang, J., Zhong, Q., Li, W., Li, S., Li, H., Wu, K. (2016). Experimental realization of two-dimensional boron sheets. Nature Chemistry, 8(6), 563-568. https://doi.org/10.1038/nchem.2491, respectively. As can be seen from the figure, large scale homogeneous borophene has been formed. From further observations a size of at least 1 x 1 pm2 was confirmed. Large borophene domains on fully covered lr(111) exceeding lateral sizes reported previously by more than one order of magnitude were obtained. White protrusions observed on top of the borophene layer in the STM spectra correspond to physisorbed 3D clusters, as indicated by the ease of displacing them with the STM tip and the lack of additional boron bonds observed in the XPS B 1s. They could be originated by trace contaminants present in the UHV chamber, such as N¾ O2 or H2O.
The growth of borophene on a weaker interacting support, namely Cu(111), was also carried out in order to assess the applicability of the CVD method to a wider range of metal substrates. Cu is a particularly interesting substrate in view of applications. It is a readily accessible material whose typically low interaction with supported 2D materials makes it suitable for different transfer processes to functional-relevant substrates and for scalable fabrication. Following the CVD procedure described above for the case of lr(111), 0.23 L of diborane gas were dosed onto a Cu(111) single-crystal kept at 773K. The resulting product was characterized by STM, revealing the presence of single-crystalline domains. Even at low coverage (around 40%), the domains extend over hundreds of nanometers, which, together with the low density of nucleation sites, anticipates that much larger domains can be achieved. Detailed inspection of the domains by high resolution STM imaging allows the characterization of their in-plane periodic structure. Albeit presenting distinct appearances at positive and negative bias, the structure can be described by a unit cell with |a| = 15.57 ± 1.0 A° , |b| = 21.5 ± 1.0 A° that form an angle of f = 73°, consistent with the fast Fourier transform image. It leads to the formation of mirror-symmetric domains aligned along the three high-symmetry axis of Cu(111). Structure and STM appearance are in agreement with the x3-like borophene polymorph (defined by h = 1/5) on Cu(111). The formation of c6 and c3 borophenes on lr(111) and Cu(111) by deposition of diborane, strongly suggests that the molecular precursor undergo pyrolytic decomposition assisted by the catalytic surfaces, thus prompting a 2D growth. The large lateral dimensions of the single-crystalline domains suggest a carpet-like 2D growth mode characterized by low nucleation density and high diffusion rates of mobile species. Furthermore, a more detailed analysis of the growth was carried out. CVD of diborane gas on lr(111) as above (under growth conditions of 0.23L and substrate temperature of 1223K) yield c6 borophene in a single-crystalline domain of a planar overlayer with stripy appearance, presenting a mirror-symmetric zigzag-like appearance, which can be described by the unit cell with lattice vectors |a| = 16.2 ± 1.0 A, |b| = 5.2 ± 1.0 A forming an angle of F = 60°. Large single-crystalline domains fully covering the substrate (at least a few hundred of nm) and extremely low density of borophene edges were observed by STM (scanning tunneling microscopy). It was observed that borophene forms different rotational single-crystalline domains on lr(111). In order to determine their allowed orientations, the zigzag stripes of independent domains were measured. Three equivalent rotational single-crystalline domains extending over large areas of at least hundreds of nanometers of lateral size were found, each of them having the stripes aligned along one of the three high-symmetry axis of the underlying surface ([10-1], [110] and [011]). Therefore, borophene on lr(111) forms three equivalent domains, compatible with the reported stacking of borophene on lr(111)
No bare lr(111) areas and no indication of borophene second layers were observed by STM, revealing that borophene fully-covers the substrate. Further growth processes performed at higher diborane doses yielded the same coverage, thus indicating that the process can be self-limited to one single-atomic borophene layer, and strongly suggests that the molecular precursor undergoes dehydrogenation reactions assisted by the catalytic surface. On the other hand, the large dimensions of the single-crystalline domains at the indicated growth temperature, indicates a carpet-like 2D growth mode characterized by low nucleation density and high diffusion rates of intermediate boron species.
Complementary XPS chemical characterization of the polymorph grown by CVD confirmed the absence of nitrogen and presence of boron in the 2D sheet. The B 1s core-level signal consists of a symmetric peak that can be well-reproduced by a Voigt-like function centered at 188.7±0.1 eV binding energy, thus being shifted by 1 - 1.6 eV with respect to other borophenes on Ag(111) and Cu(111) in the state of the art. The shift is consistent with the reduction of adsorption distance on I r( 111 ) (2.1 A) compared to Ag (111) (2.4 A) and Cu(111) (2.3 A), and points towards a stronger borophene-substrate interaction for lr(111), reminiscent of the trend observed for other 2D materials. The full width at half maximum of 1.3 eV (larger than the energy resolution of the apparatus ~ 1 eV) of the B 1s peak suggests a multiple-peak sub-structure. This could be explained by the large variations of charge density within this borophene sheet on lr(111) and/or the presence of diverse B bonding schemes with heteroatoms residually present, e.g. from the precursor or the synthesis chamber.
CVD-grown borophene on Cu(111) exhibits domains with a periodic structure defined by a rhomboidal unit cell. The evaluation of the fast Fourier transforms (FFT) calculated for independent borophene domains reveals that these prefer to grow forming two mirror- symmetric structures, each one rotated by 5.0±1.5°. In addition, these mirror-symmetric domains can also grow along three different orientations rotated by 120°, thus forming a 3- fold alignment of pairs of mirror-symmetric domains with the (111) surface. This result corroborates the (V73xV39)R ± 5.8° on Cu(111) superstructure reported before, hence endorsing the identification of our borophene polymorph as c3— like polymorph.
STS spectra measured on borophene grown on lr(111) present a minimum of dl/dV intensity at the Fermi level, as well as linear l(V) relation that denotes the metallic character of borophene.
Depending on residual gases and/or impurities, also borophene with heteroatoms at random positions, particularly O and/or N, and/or on the rim of borophene domains, were also produced, as was proven by XPS. Particularly heteroatoms could be found at the rim of borophene, depending on experimental conditions. Respective results could e.g. derived from B1s XPS.
Furthermore, depending on experimental conditions, e.g. the partial pressure or exposure time of the precursor gas, and/or substrate temperature, also structures comprising boron clusters, e.g. derived from tetrahedrons, octahedrons and/or icosahedrons, either isolated or connected, also could be observed, which is also to be expected from the extremely variable bonding chemistry of boron. Again, depending on impurities, also heteroatoms could be included in such clusters. Such clusters might account to a broadening in the lower binding region in XPS spectra observed.
Example 2: Production of lateral interfaces of a borophene with hexagonal boron nitride A film was produced as in Example 1, except that at certain points in time the cold trap 2 was deactivated, resulting in lateral interfaces of borophene with hexagonal boron nitride (h BN). Again, large borophene domains on fully covered lr(111) exceeding lateral sizes reported previously by more than one order of magnitude were obtained, with atomically precise lateral interfaces to h BN.
The precursors for borophene and h BN were selectively dosed by activating and deactivating the cold trap, as they coexist in the same precursor gas. Hence, 0.03 L of borazine were dosed onto lr(111) kept at 1233 K in a first step, followed by 2.7 L of diborane in a second step. The dose of borazine corresponds to that of sub-monolayer growth of h BN, therefore allowing enough free catalytic surface for the following borophene synthesis. The resulting 2D layer reveals coexisting domains of borophene and h BN that fully cover the lr(111) surface, hence forming lateral heterostructures. An exemplary lateral heterostructure of the produced borophene and h BN with a sharp interface is shown in Fig. 5, a structure that is not feasible to obtain by other methods. The STM image in Fig. 5(a) therein shows a higher magnification than the one in Fig. 5(b), clearly showing the sharp border between the two structures. Borophene domains feature the three orientations and the stripy appearance with zigzag motifs discussed above, while h BN domains also preserve the characteristic appearance reported for pristine /iBN/lr(111). The latter represents a single 12-on-11 moire superstructure with a periodicity of 2.89 nm, consequence of the small lattice mismatch and locked orientation along the high symmetry directions of the surface h BN zigzag edges (and the corresponding h BN symmetry axis) are oriented in parallel to the borophene stripes, which both are aligned to one of the three high-symmetry axis of lr(111). In addition, borophene edges parallel to the stripes are energetically preferred, as indicated by their prevalence in borophene islands and edges to h BN. This promotes the formation of straight heterojunctions oriented in three equivalent directions with fixed lateral stacking. Strikingly, these straight segments extend over tens of nm, in stark contrast to the irregular lateral interfaces formed by borophene and graphene. This finding is tentatively attributed to the growth temperatures of the respective 2D materials, which are equal for borophene and h BN here, but differ for borophene and graphene. The electronic transition from borophene to h BN occurs within a distance of ~ 5 A with no apparent interface states, as evidenced by a series of scanning tunneling spectra recorded across the lateral heterojunction. The low-energy electronic structure of borophene is characterized by spectral features near the Fermi level (EF), whose intensities vary laterally, matching the periodicity of the stripe-like topography. The borophene-related density of states extends to the very interface with h BN. The spectroscopical features are better visualized in the single dl/dV spectrum, where a minimum of intensity is observed around 0.7 V. While the line-shape compares reasonably well with those measured for borophenes c3 and b12 on Ag(111) and c6 on Cu(111), as produced above, the position of the minima is shifted considerably towards higher voltage. This observation is consistent with the depopulation of states near EF as compared to the cases of borophene on Ag and Cu, consistent to the charge transfer from such substrates occurring in the opposite direction (0.08e to lr(111), in contrast to 0.03 and 0.23e from Ag(111) and Cu(111) respectively). In addition, the characteristic metallic behavior of borophene is also confirmed for this c6 polymorph by the linear l(V) spectra. At the other side of the interface, h BN presents an electronic structure with lower density of states at EF, that it is spatially modulated along the moire pattern as a consequence of the registry-dependent hybridization of N with Ir atoms (36). In Fig. 2C, the crossing between dl/dV spectra corresponding to h BN "pore" and "wire" regions is consistent with the STM contrast inversion observed at different bias voltages, likewise the crossing between h BN and borophene dl/dV curves at ~ 1.5 V accounts for the contrast inversion between both 2D layers. Borophene-ZiBN lateral heterostructures grown on lr(111) by CVD were further characterized using extended STM and STS (scanning tunneling spectroscopy) characterization. Large-area STM images evidence that borophene domains preserve the three orientations reflecting the symmetry of the underlying (111) surface upon formation of lateral heterostructures with h BN. For its part, h BN domains appear oriented in three possible degenerated orientations, in which its moire superstructure is aligned along the three possible alignments of the c6 borophene stripes (i.e. along the high symmetry axis of lr(111 )). Borophene domains presented elongated shapes in the direction of its zigzag ("wavy") stripes, thus indicating that the borophene facets parallel to the stripes are energetically preferred upon lateral bonding with h BN, and that borophene crystallizes at higher temperatures than h BN during the cooling process h BN domains appear mostly truncated along the high-symmetry axis of its moire superstructure, which indicates that they preferably bond with borophene via zigzag- terminated edges. This is observed in atomically-resolved STM images. A series of dl/dV spectra around the Fermi level taken across the borophene-ZiBN interface show that the electronic transition takes place without apparent formation of interfacial states. The anisotropic growth morphology of borophene domains furthermore enabled atomically precise alignment and contacting of other subsequently grown phases like it is shown for hm. Relevance of the invention
Besides the fact that this system allows to easily grow large scale borophenes, it particularly shows the typical advantages of a process from the gaseous or otherwise atomic-molecular excited phase, particularly in a CVD process over other growth processes. A particularly important advantage is to be seen in the use of diborane gas, particularly high purity diborane gas. The present findings open new perspectives for the synthesis of borophene-type compounds, with direct impact in semiconductors, flexible/stretchable electronics, wear resistant/tribology, hard materials/interfaces, magnetic applications, biomedical applications, etc. e.g. with metal, semimetal or nonmetal interfaces, involving e.g. nanotribology, electronic, photonic and/or spintronic aspects of quantum confinement and/or further atomic-level properties, e.g. tribology, in particular for nano- and micromechanical devices, particularly in the fabrication of (semi-)conducting films for e.g. nanoscale electronic devices and applications, e.g. for energy conversion and storage systems, as e.g. disclosed in "Disclosing boron's thinnest side" (Sachdev, H. (2015). Disclosing boron's thinnest side. Science, 350(6267), 1468-1469. https://doi.org/10.1126/science.aad7021) and the review article "Sorry, graphene - borophene is the new wonder material that's got everyone excited" (MIT Technology Review: https://www.technologyreview.eom/s/613267/borophene-the-new- 2d-material-taking-chemistry-by-storm/; C&EN: https://cen.acs.org/materials/2-d- materials/Borophene-impressive-electronic-physical-properties/97/i6; IEEN Spectrum: https://spectrum.ieee.org/tag/borophene?type=BlogPost ).
With the present method, particularly tough films comprising borophenes, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D- network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron- containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B- B bonds, can be produced on a larger scale.

Claims

Claims
1. A method for the production of a structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron- containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B- heteroatom bonds are connected by B-B bonds, the method comprising: contacting at least one surface of a substrate with at least one precursor in a gaseous or otherwise atomic-molecular excited state, wherein the substrate has a temperature in the range of -196 °C to 3000 °C, and deposition of a structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D- network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron- containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B- B bonds, on the at least one surface of the substrate, wherein a pressure of the at least one precursor in the gaseous or otherwise atomic- molecular excited state is in the range of 10 10 mbar to 10 bar, and wherein the at least one precursor in the gaseous or otherwise atomic-molecular excited state comprises at least one precursor, chosen from the group of substituted and unsubstituted boranes, substituted and unsubstituted heteroboranes, substituted and unsubstituted polyboranes, substituted and unsubstituted poly-boron-heteroatom compounds, substituted poly-boron compounds, substituted and unsubstituted organoboron compounds, substituted and unsubstituted organopolyboron compounds, substituted and unsubstituted borazines, substituted and unsubstituted boroxines, and boron halides, as well as adducts of substituted and unsubstituted boranes, substituted and unsubstituted heteroboranes, substituted and unsubstituted polyboranes, substituted and unsubstituted poly-boron-heteroatom compounds, substituted and unsubstituted poly boron compounds, substituted and unsubstituted organoboron compounds, substituted and unsubstituted organopolyboron compounds, substituted and unsubstituted borazines, substituted and unsubstituted boroxines, and boron halides.
2. The method according to claim 1, wherein the at least one precursor in the gaseous or otherwise atomic-molecular excited state comprises diborane.
3. The method according to any one of the preceding claims, wherein the temperature is in the range of 22 °C to 1500 °C, optionally in the range of 500 °C to 1000 °C.
4. The method according to claim 3, wherein the substrate is pre-heated.
5. The method according to any one of the preceding claims, wherein the pressure of the at least one precursor in the gaseous or otherwise atomic-molecular excited state is in the range of 109 mbar to 104 mbar, optionally in the range of 108 mbar to 107 mbar.
6. The method according to any one of the preceding claims, wherein the substrate is chosen from a metal substrate, a semiconductor substrate, or an insulator, preferably wherein the substrate is a metal substrate, and/or, wherein the at least one surface of the substrate has essentially a homogeneous crystal structure, particularly wherein the at least one surface of the substrate comprises a (111) surface.
7. The method according to any one of the preceding claims, wherein a single layer or multiple layers of the structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron- containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron-containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B- heteroatom bonds are connected by B-B bonds, are formed on the at least one surface of the substrate, and/or wherein the at least one precursor in the gaseous or otherwise atomic-molecular excited state is dosed onto the at least one surface of the substrate.
8. The method according to any one of the preceding claims, wherein the at least one precursor in the gaseous or otherwise atomic-molecular excited state further comprises a dopant gas and/or a further boron containing compound, wherein heterostructures of boron and at least one further atom are formed in addition to the structure containing at least one borophene.
9. A product comprising a structure containing at least one borophene, and/or at least one boron-heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D- network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron- containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B- B bonds, particularly produced by the method according to any one of the preceding claims, wherein the structure containing at least one borophene, and/or at least one boron- heteroatom-domain comprising a 2D boron network, and/or a structure of a 2D-network containing a multitude of boron-containing clusters comprising B-B bonds, wherein at least one of the boron containing clusters comprising B-B bonds may comprise at least one heteroatom, and wherein the multitude of boron-containing clusters comprising B-B bonds are connected by B-B bonds or B-heteroatom bonds, preferably wherein one boron- containing cluster comprises 3 to 20 boron atoms, and/or a structure of a 2D-network containing a multitude of boron-heteroatom clusters having B-heteroatom bonds, wherein the multitude of boron-heteroatom clusters having B-heteroatom bonds are connected by B- B bonds, comprises at least one homologous domain with a size of at least 100 nm by 100 nm, preferably micrometer-sized single-crystalline domains.
10. The product according to claim 9, wherein at least one borophene and/or at least one boron-heteroatom-domain comprising a 2D boron network is present as a monoatomic layer on the surface of the substrate.
EP22706539.8A 2021-02-09 2022-02-03 Borophene synthesis Pending EP4251569A2 (en)

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