EP2782870A1

EP2782870A1 - Method for producing a graphene film

Info

Publication number: EP2782870A1
Application number: EP12788224.9A
Authority: EP
Inventors: Costel-Sorin Cojocaru
Original assignee: Centre National de la Recherche Scientifique CNRS; Ecole Polytechnique
Current assignee: Centre National de la Recherche Scientifique CNRS; Ecole Polytechnique
Priority date: 2011-11-22
Filing date: 2012-11-21
Publication date: 2014-10-01
Also published as: FR2982853A1; US20140374960A1; FR2982853B1; WO2013076164A1

Abstract

The subject matter of the invention is a method for producing a graphene film comprising the controlled growth of a graphene film, characterized in that it also comprises the following steps: - the depositing of at least one layer of metal (CM) at the surface of a substrate (S); - the continuous production of a carbon-rich buried region (CC) inside said layer of metal, performed by means of the impacting of a stream of carbon atoms and/or of carbon ions having an energy greater than approximately a few tens of electron volts, in order to penetrate a part of the layer of metal, making it possible to create and maintain said carbon-rich region, so as to form, by diffusion in said metal layer, a graphene film (CG) at the interface of said metal layer with said substrate.

Description

Method of manufacturing graphene film

The field of the invention is that of the processes for manufacturing very thin graphene layers. This type of generally conductive thin layers have the great advantage of being transparent and therefore find many applications in the field of electronics and visualization because of the excellent properties in terms of absorption and electrical conductivity of this type. of material.

Graphene is a two-dimensional carbon crystal formed of a monoatomic layer of hybridized carbon atoms sp2 (structure of a benzene ring corresponding to hexagonal cells), the graphite being formed by graphene sheets whose thickness corresponds to the size of a carbon atom. Although invented in the construction of fullerenes, carbon nanotubes and graphite, graphene had never been isolated and studied. Its very stability was disputed, as all the crystals tend to be thermodynamically unstable at a small thickness (the less bound surface atoms become predominant over those of the volume). The first graphene films were isolated in 2004 as described in the article by K.S.Novoselov et al., "Electric Field Effect in AtomicallyThinCarbon Films," Science, Vol. 306, p.666, 2004 and have been remarkably stable. These films are obtained by "exfoliation" of graphite blocks called HOPG (Highly Ordered Pyrolytic Graphite), commercial material. Graphite is a lamellar material consisting of stacks of graphene sheets and the connections between horizontal planes are weak. Exfoliation involves removing graphene planes using adhesive ribbons. The method is simple and not very reproducible, but it makes it possible to obtain graphene platelets measuring in the order of 10 to a few tens of μιτι in one of the dimensions.

Obtaining these first sheets of graphene made it possible to characterize them and to show that it was a stable, highly conductive, ambipolar material (that is to say that can present two types of conduction by holes or by electrons, it is in fact a zero gap semiconductor) and having high carrier mobilities (electrons or holes) (of the order of 10 000 to 100 000 cm ² / Vs at low temperature). Graphene can thus very advantageously be applied on the one hand to the fabrication of thin-film transistors (subject to precisely controlling the width of the ribbons, so as to open an energy gap in the strip structure of the material) and on the other hand to make transparent metal thin films available instead of ΙΊΤΟ (indium and tin oxide) in flat screens, in solar cells and generally in all applications requiring a transparent conductor. The interest of this material is proven for films with up to about four monolayers of graphene (material called FLG, for "few layers graphene"). This advantage is a major advantage, in a context where one seeks to replace ΙΊΤΟ because of the rarity and therefore the high cost of indium.

However, for practical use, it seems difficult to use the exfoliation method, the latter not allowing precise control of the thickness (that is to say the number of layers of graphene) or even the geometry of the deposit. Various methods of preparation have emerged, such as the partial oxidation of graphene, which then allows exfoliation in acid solution. It is then necessary to put the graphene in aqueous suspension and to deposit it for example by filtration or by "spray", with the problem that the layers obtained are not uniform in thickness.

In order to obtain acceptable electrical conductivity values, it is then necessary to perform a chemical reduction (to remove the intercalated oxygen). A process of this type which is nevertheless very complex is described in the article by G. Eda et al. In Nature Nanotechnology, vol. 3, p. 270, 2008. Other synthetic routes explored are the epitaxial growth by annealing at high temperature (above 1300 ° C) of silicon carbide substrates as described in the article by C. Berger, Science 312 (2006) 1 191-1 196, or the segregation of thermally induced surface (epitaxial) carbon from transition metal (ie ruthenium) transition metal monocrystals (but which do not form carbides as described in the article by P Sutter , Nat Mater 7 (2008) 406-41 1).

At the present time the most studied technique for the synthesis of graphene layers in large areas is the vapor phase deposition on polycrystalline metals (in thin layers or in sheet) from a carbon precursor such as methane. Once produced, these layers can be separated by selective etching of the support metal layer and subsequently transferred to a substrate of choice depending on the intended application.

It is recalled hereinafter for a better understanding of the rest of the description the main commonly used methods for making deposits of very thin films under vacuum.

There are "CVD" type processes for "Chemical Vapor Deposition" in which the constituent (s) of a gas phase react to form a film. The chemical reaction can be activated by plasma, this method is then called "PECVD" for "Plasma Enhanced Chemical Vapor Deposition".

There are also physical processes "PVD" for "Physical Vapor Deposition", these processes can be performed by thermal processes, including the method of molecular beam epitaxy "MBE" or sputtering.

The applicant has also filed a patent application FR 0805769 on an original process for synthesizing graphene layers, which consists in using an intermediate layer of a metal having a limited solubility range with carbon (for example nickel or copper ), then expose it to a controlled flow of carbon or carbon precursor according to a "PECVD" process and using a gaseous precursor. It is also possible to use an ion implantation method. A controlled cooling step is then performed to precipitate graphene on the surface of the metal. In the case of the "PECVD" method, a graphene layer can be obtained at the metal-substrate interface. The interface graphene layer does not need to be transferred later to another substrate (process step generally damaging to crystalline quality).

More precisely, this patent application relates to a method of controlled growth of graphene film comprising the following steps:

the production on the surface of a substrate of a layer of a metal having a phase diagram with the carbon such that beyond a threshold concentration ratio of molar concentration C _M / CM + C _c , with C _M the molar concentration of metal in a metal / carbon mixture and C _c the molar concentration of carbon in said mixture, a homogeneous solid solution is obtained;

exposing the metal layer to a controlled flow of carbon atoms or carbon radicals or carbon ions at a temperature such that the obtained ratio of molar concentration is greater than the threshold ratio so as to obtain a solid solution of the carbon in the metal;

an operation for modifying the phase of mixing in two phases respectively of metal and graphite leading to the formation of at least one lower film of graphene located at the interface: metal layer incorporating carbon atoms / substrate and a top film of graphene on the surface of the metal layer.

Other works subsequent to this patent application, notably conducted by Rice University (ACS Nano, Just Accepted Manuscript, DOI: 10.1021 / nn202923y, Publication Date (Web): 03 September 201 1) (ACS Nano, Just Accepted Manuscript, DOI : 10.1021 / nn202829y, Publication Date (Web): 02 September 201 1) describe the use of a solid source of carbon (polymer) deposited on the substrate and encapsulated by a nickel-based catalyst layer. Following heat treatment at 1000 ° C the carbon and dissolved then segregated by the nickel layer in the form of two graphene films (surface and respectively interface) as described in the previously mentioned patent of the applicant.

A second study of a Taiwanese university (Nano Lett dx.doi.org/10.1021 / nl201362n, Received: April 23, 201 1, Revised: August 1, 201 1) relates in turn, on the CVD growth of graphene to a temperature of 900 ° C., directly on a dielectric substrate, using an approach similar to that described in the Applicant's previous patent, but using a copper layer as catalyst and as a carbon source for the graphene interface growth and for the carbon diffusion (from the gaseous precursors) through the grain boundaries of the Cu layer.

These latest developments are carried out at very high temperatures (900 ° C.-1000 ° C.) or are of complex construction.

In general, it emerges from all of the aforementioned prior art that the methods proposed up to now remain high temperature, typically at 900 ° C -1000 ° C, to produce a material of exploitable quality.

Moreover, these methods proposed up to now for the synthesis of interface graphene are sequential processes comprising two steps: the incorporation of carbon in a metal and segregation, the incorporation of carbon by ion implantation is still poorly understood and difficult to control to produce graphene with well controlled characteristics and process. The Taiwanese process is more interesting in this sense because the synthesis occurs continuously but the fact of relying on the diffusion of carbon by the grain boundaries of a polycrystalline metal layer greatly reduces its interest. Indeed the graphene obtained is always polycrystalline with a grain size conditioned by the grain size of the copper layer used. Moreover, these authors recognize these important and inherent limitations, namely that it is not possible to form a continuous film at a lower temperature (below 850 ° C). When the temperature is above 950 ° C, the defect level of the film is also high. This could be due to the segregation of carbon species at the Cu-insulator interface that is formed and this faster than graphitization (dx.doi.org/10.1021 / nl201362n | Nano Lett 201 1).

It is also to be noted generally regarding the synthesis of graphene on the surface of a catalyst whether it is a metal or the substrate itself (as described in the articles: Applied Physics Letters 98, 183106 (201 1), Applied Physics Letters 98, 252107 (201 1)), that in the CVD methods known from the literature and described above, graphene is obtained following the exposure of a catalytic surface, generally a layer of nickel or copper metal, by a gaseous mixture containing a carbon precursor (methane, acetylene, alcohols, etc.) and at temperatures ranging from 500-600 ° C. to more than 1000 ° C.

The graphene layer is formed on the surface of the metal by catalytic dissociation of the carbon species and "construction" of the graphitic mesh with carbon atoms from either the gas phase or the resorption of the atoms that have diffused into the metal and / or on the surface of the metal. According to these methods, the formation of a continuous graphene layer on the surface of the metal can prevent the introduction additional carbon in the metal and possible graphical growth continues mainly with carbon from the gas phase. This has the advantage of inherently limiting the thickness of the deposited graphene layer but remains very difficult to control.

Therefore, in this context, the present invention relates to a graphene film manufacturing method comprising the controlled growth of graphene film characterized in that it further comprises the following steps:

depositing at least one layer of metal on the surface of a substrate (S);

the continuous production of a buried region rich in carbon inside said metal layer made by impinging a stream of carbon atoms and / or carbon ions with energy greater than about a few tens of electron volts, to penetrate a portion of the metal layer, for creating and maintaining said carbon-rich region, so as to form by diffusion in said metal layer, a graphene film at the interface of said layer metal with said substrate.

According to a variant of the invention, the continuous production of a buried region rich in carbon is achieved by exposing a flow of carbon atoms and / or carbon ions of sufficient energy to penetrate part of the metal layer.

According to a variant of the invention, the metal layer having a thickness of the order of a few hundred nanometers, the energy of the flow of carbon atoms and / or carbon ions is of the order of a few tens to a few hundred electrons volts.

According to a variant of the invention, the metal layer having a thickness of the order of a few tens of nanometers, the impaction is carried out at a temperature below about 500 ° C.

According to a variant of the invention, the flow of carbon atoms and / or carbon ions comprises doping species which may be boron or nitrogen.

According to a variant of the invention, the flow of carbon atoms and / or carbon ions is modulated into doping species over time. According to a variant of the invention, the metal may be nickel, or copper or cobalt, or iron, or ruthenium.

Advantageously alloys can also be used as well as multilayer systems. For example one can choose to use a thin layer of Ru at the interface with the substrate (the Ru is known for better compatibility with graphene at mesh parameter level) above which is deposited a thin layer of Cu, Ni, Co or Fe (known for better catalytic activity vis-à-vis the CVD processes). In the latter case, the growth temperature range must be adjusted accordingly in order to avoid the formation of alloys. Also ternary systems are possible for example with Ru at the interface to facilitate the formation of graphene of good quality, Ni as a top layer for good catalytic activity and a good diffusion of carbon and a very thin intermediate layer for example Cu which avoids the formation of Ni-Ru alloy while allowing the diffusion of carbon.

According to a variant of the invention, the method comprises the production of a multilayer structure comprising at least:

an interface layer allowing good crystallographic compatibility (hexagonal structure, mesh parameters) with graphene and comprising, for example, ruthenium and;

an upper layer comprising nickel, or copper or cobalt, or iron, or catalytic alloys with respect to hydrocarbons.

According to a variant of the invention, the substrate may be glass, quartz, sapphire, alumina, magnesium oxide.

According to a variant of the invention, the continuous production of said carbon-rich zone is obtained by a PECVD-type growth process comprising the following steps:

the creation of a plasma comprising ionized carbonaceous species;

the impact of said carbonized ionized species on said metal layer under the action of an electric field.

According to one variant of the invention, the PECVD type growth process is carried out with a triode type reactor generating a stream of ionized species whose energy can be modulated independently of the plasma generation parameters. According to a variant of the invention, the PECVD type growth process is carried out in the presence of a gaseous precursor comprising an oxidizing species.

According to a variant of the invention, the continuous production of said carbon-rich zone is obtained by a MBE type process with a gas beam charged with methane in molecular form and in carbon ions.

According to a variant of the invention, the deposition of the metal layer is performed at a temperature below the temperature of formation of an alloy between said metal and said substrate.

According to a variant of the invention, the metal being nickel, the substrate being based on silicon oxide, the deposition temperature of said metal layer is carried out at a temperature between about 400 ° C and 500 ° C.

According to a variant of the invention, the method further comprises a preliminary step of cleaning said substrate chemically and / or by ion bombardment so as to avoid the potential dewetting of said metal layer on the surface of said substrate.

According to a variant of the invention, the method comprises a step of chemical dissolution of said metal layer, in order to expose, the previously formed graphene layer.

According to one variant, the manufacturing method is carried out on a water-soluble substrate that may be a KBr or NaCl salt, allowing the chemical dissolution of said metal layer and said substrate in a single step, in order to expose the coating layer. graphene previously formed, in the form of a free membrane that can be suspended.

The invention will be better understood and other advantages will appear on reading the description which follows and with reference to the appended figures among which:

FIG. 1 illustrates the structure obtained according to the process of the present invention which notably comprises the production of a region rich in carbon atoms inside a metal layer;

FIG. 2 illustrates the results of analysis by XPS spectrometry on respectively a bare substrate, a substrate covered with a nickel layer, on a substrate coated with a graphene film produced according to the method of the invention;

FIG. 3 illustrates the results of analysis by XPS spectrometry of graphene film obtained according to the process of the invention and carried out on different substrates;

FIG. 4 illustrates the results of analysis by Auger spectrometry of graphene film obtained according to the process of the invention and carried out on different substrates;

FIG. 5 illustrates the results of analysis by Raman spectrometry of graphene film obtained according to the process of the invention and carried out on different substrates;

FIG. 6 illustrates the results of fine AES analysis of graphene obtained according to the process of the invention and carried out on different substrates.

The process for producing a graphene film according to the invention comprises a step of a controlled graphene growth process which uses the deposition of a metal layer which may in particular be made of nickel, cobalt or iron or copper or ruthenium.

This layer is deposited on a substrate of interest (which may be glass, quartz, sapphire, alumina, MgO, etc.) whose choice is only constrained by the fact that in the temperature range used during the deposition, the substrate must not form an alloy with the metal layer.

The method of the present invention is based on the ability to create and maintain in this metal layer, a region rich in carbon as illustrated in Figure 1 which shows: on a substrate S, and in a metal layer C _M , the presence of a region rich in carbon species C _{c in} order to obtain a carbon concentration gradient making it possible to promote the diffusion of carbon species by the interaction of an FC flow of said carbon species towards the interface with the substrate and their segregation precipitation in the form of graphene thus allowing the formation of a graphene film at the metal layer / substrate interface.

The carbon-rich region can be created and maintained at different synthesis temperatures over the duration of the deposition, for example using a chemical vapor deposition type growth method. Plasma-assisted "PECVD" or ion implantation method, or "MBE" molecular beam epitaxy for "Molecular Beam Epitaxy" or a conjunction of both, as will be described in more detail in the following description . The carbon-rich region, located more or less close to the surface of the metal layer can be created and maintained depending on the energy and flux of ions / carbon atoms used.

More specifically, in the case of "PECVD" process, the carbon species can be ionized in a plasma and then directed towards the substrate by an electric field (obtained for example by polarizing the substrate). If the energy of the ions is suitably chosen, it becomes possible to implant the carbon in a region close to the surface of the metal layer and thus create a carbon-rich region whose depth depends on the energy of the ions, while the carbon concentration depends on the ionic flux.

The flow of ions which permanently bombard the surface of the metal layer, prevents the formation on this surface of a continuous layer (possibly graphitic) of carbon from the carbon diffusing towards the surface of the substrate as well as carbon depositing (as in conventional CVD processes) from the gas phase.

On the other hand, if a triode-type PECVD reactor configuration is used, the ion energy as well as the ionic flux can be modulated, independently of the generation and maintenance parameters of the plasma (created between two electrodes). through the bias potential applied to the substrate (the third electrode). It thus becomes possible to influence in a controlled manner the thickness of the synthesized graphene layer (number of graphitic planes).

It is also possible to use an ion implantation method (commercial or as described below), or an MBE method or a conjunction of these two methods. In this case, a region rich in carbon, located more or less close to the surface of the metal layer can be created and maintained according to the energy and the flow of ions / carbon atoms used.

It should be noted that in this process, the continuous formation of graphene on the surface of the metal is to be avoided as this may prevent the carbon feed of the carbon-rich region that one wishes to create in the metal layer.

The proposed method thus makes it possible to obtain graphene layers directly on substrates of interest (growth at the interface) in a single step (continuous and controllable growth).

Moreover, the thickness of the synthesized graphene layer (the number of graphitic planes) can be modulated mainly by the exposure time (or the flux (dose) in carbon atoms introduced into the metal layer) and the depth of the graphene layer. introduction (correlated both to the energy of introduced species and to the diffusion length of carbon atoms to the interface which is related to the temperature and thickness of the metal layer).

The method of the present invention also has the advantage of inherently enabling:

to be able to synthesize, in a simple and controlled manner, graphene films doped by the addition of doping elements (for example nitrogen or boron) in the gaseous source;

- Being able to synthesize in a single step of manufacturing modulated doping films by changing during the deposition type doping elements.

Example of a process for manufacturing a graphene film according to the invention and validation of the production of graphene film:

Different types of silicon oxide substrate have been used in various forms: glass (softening point around 550 ° C.), quartz, fused silica (softening point around 800 ° C.), thermal silica on wafer silicon Si (100).

A layer of approximately 100 nm of nickel is deposited by ultraviolet evaporation on a substrate heated to 450 ° C., a temperature generally equal to that used subsequently for the synthesis of graphene. This method (deposition of hot nickel and not at room temperature) is selected to avoid any dewetting of the nickel layer after the rise to the synthesis temperature.

Prior to the deposition of nickel, the substrates are cleaned chemically, then under vacuum in a "UHV" frame for "Ultra High Vacuum", by ionic bombardment of Ar ⁺ ions, in order to eliminate all trace of contaminants (including carbon ) at the interface. The surface quality is monitored at each step by X-ray photoelectron spectrometry techniques, "X-Ray photoelectron spectrometry" commonly referred to as "XPS" spectrometry, or Auger spectrometry or Raman spectrometry.

The substrates thus prepared are thereafter:

transferred into a PECVD type triode frame and exposed to a CH ₄ plasma (30% H ₂ ) for 3 minutes typically at a temperature of 450 ° C. On glass, two other synthesis temperatures 500 ° C. and 550 ° C. were tested. During deposition, from the main plasma, an ion current of about 0.6 A / cm ² is extracted for an extraction potential applied to the 100 V substrate. A cleaning plasma is applied at the end of the deposition for 10 minutes at a temperature of 100 to 160 ° C in order to remove any carbon deposit on the surface of the samples;

- held in the UHV frame and exposed to a hot (450 ° C) beam (type MBE) gas containing methane (in molecular form) and carbon ions and methane and a small proportion of hydrogen from the dissociation of CH ₄ . This beam is generated through a commercial ion bombardment source. The ion energy as well as the ionization rate and flux can be modulated precisely over a wide range (from 100eV to more than 3keV ± 2eV, from 0.05 to a few tens of μΑ / cm ² , partial pressure in the beam from 10 ^"2 to 10 ^{" 7} mbar).

An ion energy of 250eV corresponding to the average energy of the ions typically extracted in a PECVD (triode) plasma is chosen as described above; the ion flux is set at 15μΑ / οιη ^{2 in} order to obtain for 120 minutes of exposure a "dose" equivalent to that obtained during the 3 minutes of exposure in the PECVD triode method described above (to recall a flow of 0.6mA / cm ² is used in this case). After both types of deposition, the nickel layer is removed by wet etching (commercial Ni-etchant: Nickel Etchant TBF - Transene). In all cases, electron spectroscopy (XPS, Auger) and Raman spectroscopy demonstrate the formation of an interface graphene layer from carbon that has passed through the nickel layer from the gaseous source.

These results are presented in more detail below.

The XPS analysis focused on:

on the surface of a substrate (less than 10 nm depth analyzed) after cleaning (curves C _2A in FIG. 2, the abscissa axis is relative to the binding energy and the ordinate axis is in arbitrary unit );

on the substrate plus the deposition of the nickel layer (curve C _2B of FIG. 2);

and on the substrate plus the graphene film and the Ni layer, after a complete process of interfacial graphene synthesis (including residual carbon cleaning at the surface of the nickel layer) (curve C ₂ c of Figure 2). Note the absence of carbon (residual carbon cleaning on the surface of the nickel layer), indicating that if after the dissolution of the nickel layer there is carbon in the form of graphene, its provenance at the interface is linked to diffusion through the nickel layer which has retained its integrity (not by diffusion at the grain boundaries) ,.

Another XPS analysis was conducted from graphene film made on different substrates, after graphene synthesis and dissolution of the nickel layer, these different substrates are respectively:

a quartz substrate (softening point greater than 1000 ° C. and PECVD growth method at 450 ° C. (curve C ₃ A of FIG. 3);

a glass substrate (softening point 550 ° C) and PECVD growth method at 450 ° C (curve C ₃ B of Figure 3); a thermal silica substrate on Si (100) substrate (SIO ₂ / Si) and MBE type growth method with implantation of carbon ions of 250 eV at 450 ° C (curve C _3C of Figure 3);

fused silica substrate "fused SiO ₂ " and PECVD growth method at 450 ° C (curve C ₃ D of Figure 3);

a glass substrate (softening point 550 ° C.) with a PECVD growth process at 550 ° C. (curve C ₃ E of FIG. 3).

Note the presence of carbon on all samples, regardless of the type of interface and type of growth process (PECVD or MBE). The graphitic nature (graphene) of the carbon layer formed on the surface of a substrate according to the process of the invention is confirmed by the curves of FIG. 4 (the abscissa axis is relative to the kinetic energy and the the y-axis is relative to an arbitrary unit) and 5 respectively obtained by Auger spectroscopy (AES) and Raman.

More precisely, the AES analysis of the surface (grazing incidence of the electron beam allowing an analysis of less than 2 nm depth) of the samples after interface graphene synthesis and dissolution of the nickel layer respectively. We note the presence of graphitic carbon on various tested substrates. The curves are respectively relative to glass substrates with a PECVD growth process at 450 ° C. (curve _C.sub.4E ), at 500.degree. C. (curve _C.sub.4A ) and at 550.degree. C. (curve _C.sub.4B ), fused silica. SIO ₂ "with PECVD growth process at 450 ° C (curve C _4C ), SIO ₂ / Si with MBE type growth process with carbon ion implantation of 250eV at 450 ° C (C _4D curve), and quartz with PECVD growth method at 450 ° C (curve C _4F ).

The graphene-type nature (presence of the 2D band around 2700 cm ^-1 is confirmed by the Raman analysis illustrated by the curves of FIG. 5. The curves C5A, C5B, C5C, C5D are respectively relative to substrates of SI0 ₂ / Si and MBE type growth method, with implantation of carbon ions of 250eV at 450 ° C and SIO ₂ / Si respectively, glass and quartz with a PECVD growth process at 450 ° C.

The confirmation of the presence of graphene is reinforced by the fine AES carbon analysis illustrated by the curves of Figure 6 clearly indicating the graphitic nature of the deposit. The very thin of the layer (graphene FLG) is confirmed by the transparency of the deposit (as a reminder a graphene monolayer absorbs 2.3%, ten layers 23%). The curves of Figure 6 correspond respectively to the glass substrates, with growth method PECVD at 450 ° C (curve C ₆ E) 500 ° C (curve C ₆ A) and 550 ° C (curve C _4B) of "fused SI0 ₂ " fused silica and PECVD growth process at 450 ° C. (curve C ₆ c), SiO ₂ / Si and MBE type growth method with implantation of carbon atoms at 250 ° C. at 450 ° C. (curve C ₆ D), and quartz with PECVD growth process at 450 ° C (curve C ₆ F) - It should be noted that by choosing suitable experimental conditions, the MBE (UHV) process can reproduce the growth conditions of the PECVD process triode (the layers of graphene obtained are very comparable).

The triode PECVD process is a fast process that can be easily integrated into an industrialized flow. The operating conditions of growth in this case are reproducible and effective, but the field of parameters to be optimized is very large (typically more than 14 parameters sometimes interdependent). Nevertheless, being able to reproduce the triode PECVD environment in a UHV process represents a major advance for the following reasons:

- we can indeed consider a general mechanism of synthesis;

the UVH process is a slower and inherently extremely clean process (residual vacuum of ^10-11 mbar), accurate and reproducible (characteristics known for example in MBE approaches);

- by the UHV process, it is possible to explore a very wide range of environments and growth conditions with unparalleled control and reproducibility of each parameter. This means that it becomes possible to develop growth operating conditions to obtain the best possible graphene quality for a given substrate and growth temperature;

the operating conditions developed with the precision and degree of understanding inherent in the UHV process can be very easily transposable in the triode PECVD process. So we have at the same time a very valuable tool for study / development of processes by the UHV approach and a simpler and faster method of synthesis (PECVD triode) in which one can directly implement the developments obtained by the first approach.

Claims

CLAIMS 1. A process for manufacturing a graphene film comprising the controlled growth of graphene film, characterized in that it further comprises the following steps:

depositing at least one metal layer (CM) on the surface of a substrate (S);

- the continuous realization of a buried region rich in carbon

(Ce) within said metal layer effected by impinging a flow of carbon atoms and / or carbon ions with energy greater than about a few tens of electron volts, to penetrate a part of the metal layer, for creating and maintaining said carbon rich region, so as to form by diffusion in said metal layer, a graphene film (CG) at the interface of said metal layer with said substrate.

2. A method of manufacturing graphene film according to claim 1, characterized in that the metal layer having a thickness of the order of a few hundred nanometers, the energy of the carbon atom flux and / or Carbon ions are of the order of a few tens to a few hundred electron volts.

3. Graphene film manufacturing method according to claim 2, characterized in that the metal layer having a thickness of the order of a few tens of nanometers, the impaction is performed at a temperature below about 500 ° C.

4. Process for the production of graphene film according to one of claims 1 to 3, characterized in that the flow of carbon atoms and / or carbon ions comprises doping species that may be boron or boron. nitrogen.

5. A method of manufacturing graphene film according to claim 4, characterized in that the flow of carbon atoms and / or carbon ions is modulated into doping species over time.

6. A method of manufacturing graphene film according to one of claims 1 to 5, characterized in that the metal may be nickel, or copper or cobalt, or iron, or ruthenium or alloys of these metals .

7. A method of manufacturing graphene film according to one of claims 1 to 5, characterized in that it comprises the production of a multilayer structure comprising at least one interface layer for good crystallographic compatibility with graphene, for example, ruthenium and an upper layer of nickel, or copper or cobalt, or iron, or catalytic alloys with respect to hydrocarbons.

8. Graphene film manufacturing method according to one of claims 1 to 7, characterized in that the substrate may be glass, quartz, sapphire, alumina, magnesium oxide.

9. A method of manufacturing graphene film according to one of claims 1 to 8, characterized in that the continuous production of said carbon-rich zone is obtained by a PECVD growth method comprising the following steps:

the creation of a plasma comprising ionized carbonaceous species;

the impact of said carbonized ionized species on said metal layer under the action of an electric field,

10. A graphene film manufacturing method according to claim 9, characterized in that the PECVD type growth process is carried out with a triode type reactor generating a stream of ionized species whose energy can be modulated independently of the parameters of FIG. plasma generation.

1 1. A process for producing a graphene film according to claim 10, characterized in that the growth method of the type PECVD is carried out in the presence of a gaseous precursor comprising an oxidizing species.

12. A method of manufacturing graphene film according to one of claims 1 to 8, characterized in that the continuous production of said carbon-rich zone is obtained by a MBE-type process with a gas beam loaded with methane in form. molecular and carbon ions.

13. A method of manufacturing graphene film according to one of claims 1 to 12, characterized in that the deposition of the metal layer is performed at a temperature below the alloy forming temperature between said metal and said substrate.

14. A graphene film manufacturing method according to claim 13, characterized in that the deposition of said metal layer is carried out at a temperature equal to or close to the temperature used for the growth of the graphene film in order to avoid possible dewetting effects.

15. Graphene film manufacturing method according to one of the preceding claims, characterized in that it further comprises a preliminary step of cleaning said substrate chemically and / or by ion bombardment so as to avoid any potential contamination of the substrate. the interface between said metal layer and the surface of said substrate.

16. Graphene film manufacturing method according to one of the preceding claims, characterized in that it comprises a step of chemical dissolution of said metal layer, in order to expose, the previously formed graphene layer.

17. Graphene film manufacturing method according to one of the preceding claims, characterized in that it is carried out on a water-soluble substrate may be a salt of KBr or NaCl, allowing the chemical dissolution of said metal layer and said substrate in a only step, to expose, the previously formed graphene layer, in the form of a free membrane that can be suspended.