FR2957925A1 - SINGLE-PIECE ORGANOMETALLIC POLYMERS AND PROCESS FOR SYNTHESIS - Google Patents

Abstract

A method of synthesizing a monolayer polymer on a surface, comprises deposition steps on a surface of an organic precursor having the "tetracyano" functionality and a metal precursor, the organic and metal precursors being deposited in the vapor phase under a pressure below 10-6 Pa, the surface being at a temperature below the sublimation temperature of the organic precursor at this pressure.

Description

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SINGLE-PIECE ORGANOMETALLIC POLYMERS AND PROCESS FOR SYNTHESIS

The present invention relates to the production of organized molecular networks, and in particular two-dimensional polymers or atomic monolayer. The production of organized molecular networks makes it possible to envisage numerous applications in the field of microelectronics and nanoelectronics. A decisive step has been taken recently with the realization of two-dimensional networks whose cohesion is ensured by covalent bonds, formed by activating a chemical reaction directly on a surface. The formation of such networks, based on the possibility of extending a two-dimensional polymerization reaction, is described, for example, in Zwaneveld N.A. Pawlak R .; Abel M .; Catalin D .; Gigmes D .; Bertin D .; L. Door, "Organized Formation of 2D Extended Covalent Organic Frameworks at Surfaces" Journal of the American Chemical Society 2008, 130, (21), 6678-6679. The present invention relates more particularly to processes for obtaining phthalocyanine polymers. Especially because of their optoelectronic and catalytic properties, phthalocyanine polymers have been widely studied for thirty years. These polymers are generally obtained by chemical methods in solution or in vapor phase, or even possibly by co-evaporation. Yudasaka M .; Nakanishi K .; Hara T .; Tanaka M .; Kurita S., "Formation of Copper Phthalocyanine Polymer-Films by the Double Source Evaporation of Tetracyanobenzene and Copper" Japanese Journal of Applied Physics Part 2-Letters 1985, 24, (11), L887-L889, and Yudasaka M .; Nakanishi K .; Hara T .; Tanaka M .; Kurita S .; Kawai M., "Meta) Phthalocyanine Polymer Film Formation by the Double Source Evaporation of Tetracyanobenzene and Metal" Synthetic Metals 1987, 19, (1-3), 775-780, describe methods for forming phthalocyanine and copper polymers, by co-evaporation of tetracyanobenzene and copper on a quartz substrate, under argon atmosphere at a pressure between 0.01 and 0.1 Pa. The resulting polymers have a three-dimensional entangled shape or a form of

thick layer (1 to several μm), in which structural and / or chemical defects appear in large numbers. Due to the presence of these defects, the properties of the polymers obtained vary according to the conditions of their formation.

It is therefore desirable to produce monolayer or two-dimensional metal phthalocyanine polymers having a sufficiently low number of defects so as not to disturb the physical and chemical properties of the polymer. It is also desirable that the properties of the chosen metal appear in the resulting polymer. Embodiments relate to a method of synthesizing a monolayer polymer on a surface, characterized in that it comprises steps of depositing on a surface of an organic precursor leading to the formation of phthalocyanines and a metal precursor in the vapor phase at a pressure of less than 10-6 Pa, the surface being at a temperature below the sublimation temperature of the organic precursor at that pressure. According to one embodiment, the organic precursor has the "tetracyano" functionality. According to one embodiment, the metal precursor has magnetic properties. According to one embodiment, the surface has an oriented crystalline structure. According to one embodiment, the surface is formed by a silver, copper or gold substrate, or an electrically insulating material. According to one embodiment, the substrate is a monocrystalline silver surface Ag (111) or Ag (001). According to one embodiment, the deposition pressure on the surface of the metal and organic precursors is less than 10-8 Pa. According to one embodiment, the organic and metallic precursors are deposited on the surface in stoichiometric proportions of the surface. polymerization reaction. According to one embodiment, the method comprises successive stages of deposition on the surface of the organic precursors, then deposition on the surface of the metal precursors.

According to one embodiment, the organic and metal precursors are deposited simultaneously on the surface in the stoichiometric proportions of the polymerization reaction. According to one embodiment, the organic precursors are tetracyanobenzene or tetracyano-naphthalene molecules. According to one embodiment, the metal precursors are atoms of two different metals. According to one embodiment, the method comprises a step of forming a second layer of monolayer M-phthalocyanine molecules on a first monolayer polymer layer formed on the surface. According to one embodiment, the metal precursors used to form the two layers of monolayer M-phthalocyanines have magnetic properties. Embodiments also relate to a monolayer polymer formed on a surface, characterized in that it comprises a mesh structure of M-phthalocyanine monolayer atomic, M being a metal.

Exemplary embodiments of the invention will be described in the following, without limitation in connection with the accompanying figures in which: Figure 1 shows a chemical reaction forming a metal phthalocyanine polymer, according to a method of FIG. 2 shows the atomic structure of the metal phthalocyanine polymer, FIGS. 3A, 3B are images obtained using a tunneling microscope, an atomic monolayer of a metal phthalocyanine polymer formed. 4 is an image obtained by means of a tunneling microscope, an atomic monolayer of 1,2,4,5-tetracyanobenzene molecules deposited on a substrate, FIG. the atomic structure of an assembly of several 1,2,4,5-tetracyanobenzene molecules in the atomic monolayer of FIG. 4,

FIG. 6 represents a chemical reaction for forming an octacyano-M-phthalocyanine molecule that can be produced by the reaction of 1,2,4,5-tetracyanobenzene molecules with a metal atom, FIG. the atomic structure of an octacyano-M-phthalocyanine molecule, FIG. 8 is an image obtained using a tunneling microscope, an atomic monolayer assembly of octacyano-M-phthalocyanine molecules, 9 shows a chemical formula of a monolayer metal phthalocyanine polymer, according to another embodiment, FIG. 10 represents a chemical reaction of formation of a metal phthalocyanine polymer, obtained by polymerization of tetracyano-naphthalene in FIG. the presence of a metal, FIG. 11 represents a chemical reaction of formation of a metal phthalocyanine polymer, obtained by polymerization of a molecule comprising the "tetracyano" function, in the presence of a n metal. In the following description, many details are described to allow a sufficient understanding of the described embodiments. The described embodiments may be obtained without one or more specific details presented, or in particular by other methods, equipment and materials. In other described embodiments, well-known materials or operations are not indicated or described so as not to affect the clarity of the description. In the following description, the term "according to one embodiment" indicates that a particular feature described in connection with an embodiment is simply included in at least one embodiment. Thus, if this term is used in various places of the description, it does not necessarily refer to a single embodiment. In addition, the described features can be suitably combined in one or more embodiments. In the following description, the term "monolayer" means a single layer of atoms deposited on a substrate. According to one embodiment, an atomic monolayer polymer of metal phthalocyanine is produced directly on a substrate by 1,2,4,5-tetracyanobenzene (TCB) PVD (Physical Vapor Deposition) vapor deposition and a metal. TCB molecules and metal atoms are covalently bonded together to form a two-dimensional, stable monolayer polymer on the substrate, in accordance with the polymerization reaction shown in Figure 1, wherein: N n wherein M are metal atoms , and "~ H" is a molecule of TCB. Figure 2 shows the atomic structure of the obtained M-phthalocyanine polymer. In FIG. 2, the M-phthalocyanine polymer has an atomic, plane, meshed, pi-conjugated monolayer structure with substantially square meshes, the M metal atoms appearing at the nodes of the mesh structure at the center of an organic structure. with four lobes, the nodes being interconnected by an organic structure comprising a benzene ring, these organic structures comprising carbon atoms C, nitrogen N and hydrogen H. In this structure the metal atom M is linked by covalent bonds to the four nitrogen atoms closest to it. FIGS. 3A, 3B show images obtained using a Scanning Tunneling Microscope (SCM) tunneling microscope when the selected substrate is monocrystalline silver Ag (III) and the metal M of iron. In these images, the distance between the centers of two adjacent meshes in two perpendicular directions is measured at 1.2 nm to 0.1 nm. This

Reduced distance reveals the formation of covalent bonds within the polymer obtained, and therefore a relatively strong cohesion of the polymer. These images also reveal an extremely high order, that is to say a very even distribution of the atoms within the polymer obtained, as well as a reduced number of defects (less than 1%). FIG. 3A also shows the atomic structure of a part of the polymer obtained in superposition on the image. Three different orientations of the M-phthalocyanine polymer can be observed with respect to the substrate, reflecting the C3 symmetry of the Ag (111) surface. The physical properties of the polymer obtained appear to be preserved since they are insoluble in water and maintained at a temperature of between 400 and 500 ° C. It turns out that the properties, especially optoelectronic and catalytic phthalocyanines, of the monolayer polymer obtained are also preserved, because it forms a well-ordered set of active centers (around a metal atom), connected by a network. organic conductive. Due to the mesh structure of the monolayer polymer, it is nano-porous. It can thus serve as a mask or a model for the deposition of metal particles or of functional molecules such as fullerenes, or biological molecules. The presence of metal atoms M and the pi-conjugation of the polymer makes the monolayer structure electrically conductive. To exploit this property, the substrate can be chosen electrically insulating. For example, the substrate chosen may be silica (SiO 2) or sapphire. Furthermore, the metal M can be chosen according to the desired properties of the monolayer polymer obtained. Thus, if the selected metal has magnetic properties such as iron, the M-phthalocyanine polymer has these properties. The resulting M-phthalocyanine polymer can thus be a highly ordered arrangement of isolated magnetic atoms of very high density. Moreover, by differentiated spin calculations, it is possible to demonstrate very different state densities around the Fermi level as a function of the spin, thus revealing spin-dependent conductive properties (spintronic).

The properties of the M-phthalocyanine polymer obtained can also be modified by changing or combining several metal precursors (Co, Ni, Zn, Ti, ...). Thus, in one embodiment, two different metals can be inserted into the polymer so as to appear alternately in its mesh structure. The two metals chosen may be magnetic and non-magnetic. It is thus possible to control the spin density of the M-phthalocyanine polymer obtained. More generally, all the metals can be used in the polymerization reaction, since the size of the atoms of the metal is compatible with the space available within the knots of the mesh structure of the polymer obtained. In a first embodiment, the monolayer M-phthalocyanine polymer is formed in two stages, by PVD (Physical Vapor Deposition) vapor deposition of TCB molecules on a substrate, followed by vacuum vapor deposition. PVD of metal atoms on the substrate. When they are deposited on the substrate, the TCB molecules are evenly distributed on the substrate to form a hexagonal mesh network, observable in FIG. 4. FIG. 4 thus represents an image obtained using a STM microscope, a monolayer mesh network of TCB molecules deposited on the substrate. The meshes of this network have a width of about 1 nm (to the nearest 0.1 nm). FIG. 5 represents the atomic structure of several TCB molecules of the network observed in FIG. 4. The cohesion of this network, which is ensured by weak hydrogen bonds, proves to be fragile and is rapidly destroyed if the temperature increases. When the metal precursor M is deposited on the substrate, it can be observed the formation of octacyano-M-phthalocyanine MPc (CN) 8 molecules in accordance with the chemical formula shown in FIG. 6, as follows: FIG. Atomic level of a molecule of MPc (CN) 8. In FIGS. 6 and 7, the MPc (CN) 8 molecule has the same structure as the nodes of the monolayer M-phthalocyanine polymer of FIGS. 1 and 2, with a metal node M and four branches formed of TCB radicals analogous to those interconnecting the metal knots of the meshes of the monolayer phthalocyanine polymer. As the metal atoms are deposited, the octacyano-M-phthalocyanine molecules spontaneously self-organize on the substrate in a dense square-mesh phase. FIG. 8 is an image obtained by STM microscope of this structure, when the substrate is in Ag (111) and when the selected metal M is iron. It appears in FIG. 8 that the octacyano-Fe-phthalocyanine molecules formed on the substrate are organized into a 1.6 × 1.6 nm square-mesh structure (to within 0.1 nm). The polymerization reaction terminates when the M metal atoms are sent to the substrate in the stoichiometric proportions of the polymerization reaction, relative to the TCB molecules (2 TCB molecules for one metal atom). No reaction byproduct occurs during the polymerization reaction. In the case where the metal precursor M is in excess of the organic precursor TCB, given the stoichiometric proportions of the polymerization reaction, the formation of metal clusters can be observed. When the metal precursor M is iron, the clusters have a width of about 5 nm and a height of about 0.5 nm. This phenomenon is explained by the fact that at room temperature, the surface mobility of the metal atoms on the substrate is large and the growth kinetics of the clusters is greater than that of the polymerization. According to another embodiment, the monolayer M-phthalocyanine polymer is formed by simultaneous PVD deposition, or co-evaporation or

simultaneous evaporation of TCB molecules and metal M atoms on the substrate, respecting the stoichiometric proportions of the polymerization reaction. In the embodiments previously described, the deposition of organic precursors TCB and metal M in the PVD vapor phase is carried out under ultrahigh vacuum (at a pressure of less than 10-5 Pa, and preferably less than 10 Pa). The TCB molecules can be evaporated by an evaporator, for example of the Knudsen cell type, maintained at the sublimation temperature of the TCB, ie 100 ° C. (to within 10%) if the pressure is at 10- $ Pa. metal precursor M can be vaporized from a bar of ultra pure metal heated by electron bombardment or from a Knudsen cell. The substrate is for example silver oriented Ag (111), maintained at a temperature below the sublimation temperature of TCB molecules, for example at room temperature (between 10 and 30 ° C). It has been discovered that TCB molecules are highly mobile on a monocrystalline Ag (111) substrate at room temperature, and that the reaction with metal atoms occurs directly and spontaneously on the substrate. The substrate can be easily obtained for example by depositing an ultrathin layer of silver on mica. An ordered monolayer M-phthalocyanine polymer can also be obtained by using a monocrystalline substrate such as Ag (001) having the same square symmetry as the monolayer polymer. The use of such a substrate makes it possible to easily control the stoichiometry of the deposited precursors and thus the formation of polymerized phthalocyanines or otherwise. Other substrates such as monocrystalline copper and gold can of course be used. Since the substrate is kept at room temperature, organic substrates can also be used. It should be noted that the substrate influences the polymerization reaction and may allow the metal and organic precursors to meet and react together. The substrate may also have a catalyst effect with respect to the polymerization reaction. The substrate can therefore be chosen according to its wettability property by metal and organic precursors and its ability to give them a high mobility. 2957925 i0

It should also be noted that certain nodes of the mesh structure of the monolayer phthalocyanine polymer obtained may not have a metal atom. Thus, in the formula example below and in FIG. 9, one metal atom is absent in every other node of the structure, and replaced by two hydrogen atoms: The absence of metal nuclei to some Nodes of the mesh structure of the monolayer polymer can be used to obtain a polymer whose nodes are formed with metal cores of different natures. For this purpose a second metal can be deposited by PVD on the polymer, the atoms of the second metal inserted into the polymer in the nodes without a metal core. In one embodiment two layers of M-phthalocyanine polymer are formed on the substrate with one or more metal precursors having at least partly magnetic properties. The second layer may be formed by covering, directly by PVD deposition, the first layer of M-phthalocyanine polymer with a layer of M-phthalocyanine molecules, M being able to represent any metal, magnetic or otherwise. The M-phthalocyanine molecules of the second layer are absorbed epitaxially. The formation of two layers makes it possible to fix the spins of the metal atoms. The pore size of the mesh structure of the M-phthalocyanine polymer can be easily changed by replacing the organic precursor TCB with another molecule having the "tetracyano" functionality, for example a tetracyano-naphthalene, -anthracene or -pentacene molecule. ). Thus, FIG. 10 represents an NHH reaction. The mesh size and the physicochemical properties of the polymer obtained can also be modified by choosing, as organic precursor, an organic molecule having the NHHN functionality "tetracyano" "/ HH" N and incorporating one or more other X functional groups. Thus, Figure 11 shows a chemical reaction of such a molecule with a metal M. The resulting polymer has the following formula: ## STR1 ## The polymer obtained has the following formula: It will be apparent to those skilled in the art that the present invention is capable of various alternative embodiments and various applications. The invention is not limited to the use of the described substrates.

Thus, other substrates promoting the polymerization reaction can be found by conducting simple polymerization tests. The invention is also not limited to the organic precursors described. Other organic precursors in which the benzene ring (s) are symmetrically functionalized for polymerization can of course be used, such as: HN NH bis (1,3-diiminoisoindoline) HN benzene-1, 2,4,5-tetracarboxamide 25

Claims (15)

REVENDICATIONS1. Process for synthesizing a monolayer polymer on a surface, characterized in that it comprises steps of deposition on a surface of an organic precursor leading to the formation of phthalocyanines and a metal precursor, in the vapor phase under a pressure less than 10-6 Pa, the surface being at a temperature below the sublimation temperature of the organic precursor at this pressure. The method of claim 1, wherein the organic precursor has the "tetracyano" functionality. 3. Method according to claim 1 or 2, wherein the metal precursor has magnetic properties. 4. Method according to one of claims 1 to 3, wherein the surface has an oriented crystalline structure. The method of claim 4, wherein the surface is formed by a silver, copper or gold substrate, or an electrically insulating material. The method of claim 5, wherein the substrate is a monocrystalline silver surface Ag (111) or Ag (001). 7. Method according to one of claims 1 to 6, wherein the deposition pressure on the surface of the metal and organic precursors is less than 10 $ Pa. 8. Method according to one of claims 1 to 7, wherein the organic and metal precursors are deposited on the surface in stoichiometric proportions of the polymerization reaction. 1315 9. Method according to one of claims 1 to 8, comprising successive steps of depositing on the surface of the organic precursors, and then depositing on the surface of the metal precursors. 10. Method according to one of claims 1 to 8, wherein the organic and metal precursors are deposited simultaneously on the surface respecting the stoichiometric proportions of the polymerization reaction. 11. Method according to one of claims 1 to 10, wherein the organic precursors are tetracyanobenzene or tetracyano-naphthalene molecules. 12. The process according to one of claims 1 to 11, wherein the metal precursors are two different metal atoms. The method of one of claims 1 to 12, comprising a step of forming a second layer of monolayer M-phthalocyanine molecules on a first monolayer polymer layer formed on the surface. 14. The method of claim 13, wherein the metal precursors used to form the two layers of monolayer M-phthalocyanines have magnetic properties. 15. Monolayer polymer formed on a surface, characterized in that it comprises a mesh structure of M-phthalocyanine monolayer atomic, M being a metal. 25 30