Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/15—Nano-sized carbon materials
  • C01B32/182—Graphene
  • C01B32/184—Preparation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y40/00—Manufacture or treatment of nanostructures
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/15—Nano-sized carbon materials
  • C01B32/182—Graphene
  • C01B32/184—Preparation
  • C01B32/186—Preparation by chemical vapour deposition [CVD]
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B2204/00—Structure or properties of graphene
  • C01B2204/20—Graphene characterized by its properties
  • C01B2204/22—Electronic properties

Definitions

• 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.
• 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.
• HOPG Highly Ordered Pyrolytic Graphite
• 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 ⁇ in one of the dimensions.
• 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 ⁇ (indium and tin oxide) in flat screens, in solar cells and generally in all applications requiring a transparent conductor.
• ⁇ indium and tin oxide
• 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 ⁇ because of the rarity and therefore the high cost of indium.
• PVD Physical Vapor Deposition
• MBE molecular beam epitaxy
• this patent application relates to a method of controlled growth of graphene film comprising the following steps:
• 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
• 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.
• 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:
• 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.
• 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.
• 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.
• the flow of carbon atoms and / or carbon ions comprises doping species which may be boron or nitrogen.
• the flow of carbon atoms and / or carbon ions is modulated into doping species over time.
• the metal may be nickel, or copper or cobalt, or iron, or ruthenium.
• Advantageously alloys can also be used as well as multilayer systems.
• a thin layer of Ru at the interface with the substrate the Ru is known for better compatibility with graphene at mesh parameter level
• the Ru is known for better compatibility with graphene at mesh parameter level
• the growth temperature range must be adjusted accordingly in order to avoid the formation of alloys.
• 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.
• 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.
• the substrate may be glass, quartz, sapphire, alumina, magnesium oxide.
• the continuous production of said carbon-rich zone is obtained by a PECVD-type growth process comprising the following steps:
• 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.
• the PECVD type growth process is carried out in the presence of a gaseous precursor comprising an oxidizing species.
• 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.
• 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.
• 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.
• 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.
• the method comprises a step of chemical dissolution of said metal layer, in order to expose, the previously formed graphene layer.
• 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.
• a water-soluble substrate that may be a KBr or NaCl salt
• 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.
• a substrate of interest which may be glass, quartz, sapphire, alumina, MgO, etc.
• 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.
• 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.
• 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 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).
• 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).
• 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).
• silicon oxide substrate softening point around 550 ° C.
• quartz 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.
• the substrates 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:
• 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 ⁇ / 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 15 ⁇ / ⁇ 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).
• the nickel layer is removed by wet etching (commercial Ni-etchant: Nickel Etchant TBF - Transene).
• 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.
• 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.
• 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.
• 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:
• 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);

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• 2011
  • 2011-11-22 FR FR1160612A patent/FR2982853B1/fr active Active
• 2012
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