Classifications

• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
  • C30B29/60—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape characterised by shape
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
  • C30B25/02—Epitaxial-layer growth
  • C30B25/18—Epitaxial-layer growth characterised by the substrate
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
  • C30B29/10—Inorganic compounds or compositions
  • C30B29/46—Sulfur-, selenium- or tellurium-containing compounds
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B33/00—After-treatment of single crystals or homogeneous polycrystalline material with defined structure
  • C30B33/06—Joining of crystals

Definitions

• the invention relates to the field of integration of 2D materials. More particularly, the invention relates to a method for integrating 2D materials onto a nanostructured substrate to obtain a monolayer of 2D materials entirely suspended. The invention also relates to fully suspended films and the use of said suspended films in different technologies.
• a two-dimensional material sometimes called a monolayer material or 2D material, is a material consisting of a single (or some) layer of atoms or molecules. Due to their unusual characteristics and for potential use in applications such as semiconductors, photovoltaics, ...
• the 2D materials of atomic thickness have unique properties (absorption, electrical conduction and thermal) and allow to consider a set of ultrafine devices, ultralight flexible etc .. however the thickness of these materials give them a very large sensitivity to the environment.
• the simple fact of depositing these materials on a substrate modifies their intrinsic properties (ex: exchange of charges). This is related to the contact surface that makes each atom of the 2D material in contact with the substrate.
• the new two-dimensional materials dichalcogenides of transition metals are the subject of important studies. The spectacular progress in controlling the electronic properties of graphene has indeed powerfully stimulated the search for new two-dimensional (2D) materials.
• the object of the present invention is to obtain a monolayer of 2D material completely suspended, without stress, that is to say the layer does not interact with the substrate.
• the present invention provides a solution to this problem by minimizing the contact areas of the 2D materials by transferring them to a nanostructured substrate.
• the present invention relates to a method of integrating two-dimensional materials on a nanostructured substrate characterized in that it comprises the following steps:
• the manufacture of two-dimensional materials by the vapor deposition method consists of:
• the transfer of said PMMA-coated materials obtained in a previous step onto a nanostructured substrate further comprises the following steps:
• the two-dimensional materials are manufactured by the exfoliation method in an inert environment and the transfer of said two-dimensional materials obtained by exfoliation on a synthesized nanostructured substrate consists of a single step of depositing said two-dimensional materials. on said synthesized nanostructured substrate.
• the nanostructured substrate is ZnO nanowires, zinc oxide, said nanostructured substrate is synthesized by a liquid phase chemical deposition method, CBD, on an SiO 2 substrate or by all other growth technologies of ZnO nanowires.
• the synthesized ZnO nanowires are disordered and of variable sizes so as to minimize the contact area with the two-dimensional materials obtained.
• the ZnO nanowires have a diameter of less than 100 nm.
• the two-dimensional materials are either molybdenum sulphide MoS 2, or tungsten sulphide WS 2 or diselenide Tungsten WSe 2.
• two-dimensional materials are any two-dimensional rigid materials.
• the invention also relates to a suspended thin film obtained by the transfer of the 2D materials onto a ZnO nanowire substrate according to the above method.
• ZnO nanowires are disordered and of varying sizes.
• the thin film suspended obtained by the above method is characterized in that the two-dimensional materials are either molybdenum sulphide MoS2, or tungsten sulphide WS2 or diselenide tungsten WSe2.
• said two-dimensional materials are Rigid and are obtained by chemical vapor deposition on SiO 2 substrate or by exfoliation deposit on an SiO 2 substrate.
• the invention also relates to the use of thin films suspended from 2D materials in the fields of electronics and / or optoelectronics and / or thermal and / or photonic.
• the invention also relates to the use of thin films suspended from 2D materials in catalysis domains and / or in ultrasensitive surfaces.
• FIG. 1 illustrates the concept and manufacture of 2D materials suspended according to the method object of the present invention
• FIG. 2 illustrates the exalted optical properties and associated band structures
• FIG. 3 illustrates the image obtained by SEM of the suspended integrated layers
• FIGS 4A and 4B illustrate the concept of active substrate.
• identical or similar elements are identified by identical reference signs throughout the figures.
• the two-dimensional materials (2D) are atomically thin semiconductors made of transition metals m- (Mo, W, Sn, etc.) covalently bound to chalcogen X- (S, Se, Te). .
• the optical and crystalline properties of these 2D materials integrated on flat substrates are still not satisfactory for an application
• the simple fact of depositing these materials on a substrate modifies their intrinsic properties (ex: exchange of loads). This is related to the contact surface that makes each atom of the 2D material in contact with the substrate.
• the present invention aims to circumvent this problem of modifying intrinsic characteristics of said 2D materials when they are transferred to a substrate, by proposing to minimize the contact surface using nanostructured substrates (carpet fakir).
• a method for integrating 2D materials onto a nanostuctured substrate is proposed.
• the first step of the process involves the development or growth of 2D materials by chemical vapor deposition on SiO 2 / Si substrates.
• the 2D materials can also be obtained by simple exfoliation and in this case simply deposited on a SiO 2 / Si substrate.
• the 2D materials are either molybdenum sulfide, MoS2, or tungsten sulfide, WS2 or tungsten diselenide, WSe2.
• the next step is to deposit a layer of PMMA on said two-dimensional raw materials in the previous step.
• the PMMA layer is used to support the single layer during chemical etching of SiO2.
• the SiO 2 substrate is etched in a hydrofluoric acid (HF) solution, diluted.
• the next step consists in transferring said 2D materials, covered with PMMA, onto nanowires of ZnO synthesized on a substrate (Si, SiO2, etc.).
• an acetone solution was used.
• the 2D materials were dried at 80 ° C to remove the residual layer of PMMA.
• the sublimation technique can be used to avoid the mechanical stresses associated with drying.
• ZnO nanowires on the silicon substrate was carried out by adopting a chemical deposition technique in liquid phase, CBD.
• 0.025 M zinc acetate was dissolved in 250 ml of water; Then 0.3 ml of ammonium hydroxide was added to the solution and stirred at room temperature. The synthesis was carried out in the absence of catalysts or metal additives. The mixture was heated to 87 ° C.
• the sample consisting of a ZnO layer previously deposited on a silicon substrate was immersed in the solution for 30 min. Then the sample was washed with water and air dried for 1 hour.
• Figure 1 shows the three-dimensional schemas of the process of simplified transfer of two-dimensional materials on ZnO nanowires.
• Fig. 1a, 1b and 1c illustrate MoS2, WS2 and WSe2 on ZnO nanowires respectively.
• the two-dimensional materials were transferred to the ZnO nanowires by a method of vapor transfer.
• Fig.ld, fig. 1 (e) and fig. 1 f are the 3D enlarged diagrams of materials, MoS2, WS2 and WSe2 on the ZnO nanowires respectively.
• Fig.1 j shows the contact between 2D materials and nanowires. Note that the contact occurs only at the edge of the ZnO nanowires.
• Fig 1k shows the spectrum of the photoluminescence intensity of said 2D materials on ZnO nanowires at room temperature.
• Raman analysis shows that the layer of 2D material is free of stress and is fully relaxed. This is due to the limited number of contact points, which is partly explained by the fact that the nanowires are not all exactly the same length and slightly disoriented with respect to the vertical axis ( Figure 1).
• the goal is to integrate the 2D material thin layer without changing its electronic structure.
• the emission factor observed in emission is explained by the direct nature of the electronic transition.
• the same 2D material deposited on a SiO 2 plane substrate becomes optically inefficient and this is explained by the indirect nature of the electronic transitions. We are talking here about the emission but the absorption is also modified.
• the final material integrated on the ZnO nanowire substrate has preserved optical properties as shown in FIG. 2.
• Figure 2 shows the optical properties and structures of the associated bands.
• the photoluminescence intensities were measured at room temperature.
• the position of the PL signal (photoluminescence) is closely related to the nature of the forbidden band, ie, it reveals a direct or indirect transition.
• the PL spectra of MoS2, WS2 and WSe2 on the ZnO nanowires are shown in Figures 2a, 2b and 2c, respectively, together with the PL spectra of the same 2D materials deposited on them.
• SiO2 substrates Said PL spectra of the 2D materials on the ZnO nanowires are represented by the gray color and on the SiO 2 substrate it is represented by the black color.
• FIG. 2d, 2e and 2f The energy spectra of the MoS2, WS2 and WSe2 materials on the ZnO nanowires and SiO2 substrate are shown in Figures 2d, 2e and 2f.
• Figures 2g, 2h and 2i show the energy band diagrams showing the optical transitions of the 2D materials on the nanowires and on the SiO2 substrate. Solid and dotted lines indicate 2D material on both nanowires and SiO2, respectively.
• the maximum of the valence band for MoS2 and WS2 on the Nanowires is the minimum of the conduction band, which results in a higher PL intensity at an increase in the bandwidth when the layer is relaxed, as shown in FIG. 2g and 2h.
• PL intensities of 2D materials can be affected by several factors such as doping and crystalline quality.
• the influence of crystalline quality can be excluded because we have deposited identical 2D materials on SiO2 substrate and on ZnO nanowires.
• the work function of ZnO is greater than the electronic affinity of all 2D materials. Therefore, the photoexcited electrons of 2D materials could be transferred to ZnO at the point of contact.
• the PL intensities of 2D materials such as MoS2 and WS2 are not more than 3 times increased charge transfer. On the other hand, the intensity PL of WSe2 is decreased by photoexcited electron transfer.
• FIGS. 4A and 4B illustrate the doping type being connected to the difference in energy level between the 2D material and that of the nanowires.
• FIG. 4A illustrates the doping n: electron injection of the nanowire to the 2D material.
• FIG. 4B illustrates the p-doping: electron transfer from the 2D material to the nanowire.
• the solution proposed by the present invention is simply limited by the size of the 2D material layer. Indeed, the ZnO nanowire substrates can be obtained on centimeter or metric surfaces (chemical growth in solution).
• ZnO zinc oxide
• the invention thus relates to a thin film suspended obtained by the transfer of 2D materials on Zno nanowires.
• the suspended thin film is obtained by the method object of the present invention described above.
• the 2D materials used for the transfer on the ZnO nanowires are of the molybdenum sulfide type, MoS2, or tungsten sulphide, WS2 or tungsten diselenide, WSe2.
• Said 2D materials are obtained by chemical vapor deposition on an SiO 2 substrate or simply exfoliated.
• Another problem that can be solved by the present invention is the control of the contact surface so as to locally be able to inject carriers (contact engineering). This is particularly interesting in that we have shown that self-supporting layers can be obtained.
• the only technique proposed today is to deposit the 2D material on a micro-perforated substrate obtained by lithography. In this case, suspended and unsprung areas are obtained. We can not speak of fully suspended layers.
• the invention furthermore relates to the use of thin films suspended from 2D materials in electronic and / or optoelectronic and / or thermal and / or photonic domains.
• the invention also relates to the use of thin films suspended from 2D materials in catalysis fields and / or in ultrasensitive surfaces.

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Families Citing this family (15)

• 2016
  • 2016-12-09 FR FR1670741A patent/FR3060023A1/fr not_active Withdrawn
• 2017
  • 2017-12-09 EP EP17832986.8A patent/EP3551788A1/de not_active Withdrawn
  • 2017-12-09 WO PCT/IB2017/057764 patent/WO2018116048A1/fr unknown

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