WO2015149116A1 - Procédé et produit de graphène - Google Patents

Procédé et produit de graphène Download PDF

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Publication number
WO2015149116A1
WO2015149116A1 PCT/AU2015/000198 AU2015000198W WO2015149116A1 WO 2015149116 A1 WO2015149116 A1 WO 2015149116A1 AU 2015000198 W AU2015000198 W AU 2015000198W WO 2015149116 A1 WO2015149116 A1 WO 2015149116A1
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graphene
substrate
vertical
plasma
hydrogen
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PCT/AU2015/000198
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English (en)
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Shailesh Kumar
Kostyantyn Ostrikov
Timothy Anthony VAN DER LAAN
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Commonwealth Scientific And Industrial Research Organisation
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Priority claimed from AU2014901223A external-priority patent/AU2014901223A0/en
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Publication of WO2015149116A1 publication Critical patent/WO2015149116A1/fr

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    • 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
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/01—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes on temporary substrates, e.g. substrates subsequently removed by etching
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/02—Pretreatment of the material to be coated
    • C23C16/0227—Pretreatment of the material to be coated by cleaning or etching
    • C23C16/0245—Pretreatment of the material to be coated by cleaning or etching by etching with a plasma
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
    • C23C16/26—Deposition of carbon only
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/30—Particle morphology extending in three dimensions

Definitions

  • the invention relates to a process for the preparation of graphene that is deposited by low temperature plasma enhanced chemical vapour deposition onto a substrate in a manner that enables facile exfoliation of the graphite from the substrate.
  • the invention also relates to graphene microwell structures preparable by such a process.
  • Graphene exhibits unique electronic, optical, chemical and mechanical properties' 11 . Because of its extremely high electron mobility (electrons move through graphene about 100 times faster than silicon), very low absorption in the visible spectrum and relative flexibility and elasticity (compared to inorganics such as indium tin oxide), supported horizontal graphene as an active functional material has been revolutionising the fields of flexible, transparent and ultra-light nano-devices, from optoelectronics 121 to sensors' 3 ' 41 .
  • graphene is normally a flat, sheet like substance, it also has the ability to be deposited onto substrates in a way that allows for a degree of vertical orientation. This allows for the creation of controlled graphene microstructures, which are potentially useful in electron emission, bio-recognition and drug/gene/protein delivery applications among others.
  • Graphene in a vertical orientation offers substantially enhanced functionality' 5 ' 61 compared to horizontally oriented graphene.
  • CVD onto metal substrates is the most promising, as high quality films of graphene can be deposited at elevated temperatures' 6 ' 121 .
  • CVD onto substrates has some underlying drawbacks - one in particular being that once the graphene has been deposited onto the substrate, it generally needs to be removed or transferred to a different substrate for use. Typically, for instance, the graphene must be transferred to a semiconductor or plastic substrate for subsequent device fabrication. Often, the removal of graphene films is via wet chemistry. Wet chemistry 191 should be avoided as far as possible in the fabrication of high quality vertical graphene films, since wet chemistry results in defect-associated 1101 loss of in-plane charge carrier transport. Loss of in-plane charge carrier transport can compromise the promising properties required for efficient field-emission, ultra-fast sensing and nano-electronics based devices' 2 ' 6 ' 111 .
  • Non wet chemical means are available, for instance, US 20120244358 describes a transfer process in which graphene is first deposited onto a conventional growth substrate, such as a copper substrate. The deposited graphene is then contacted with a transfer substrate, such as a polymer or inorganic substrate with an enhanced adhesion to graphene. This results in transfer printing of the graphene onto the transfer substrate. This avoids etching, but requires functionalised polymers as intermediates and also may require subsequent organic solvent wash out of the transfer layer.
  • CVD Another drawback with CVD is that it consumes large amounts of energy and is not particularly cost-effective for scalable fabrication. It is also a demanding process to achieve controlled graphene layer thickness and a high density of reactive open graphene edges in the vertical graphene networks at a relatively low-temperature in a cost and energy-efficient manner. Also, it is extremely difficult to simultaneously achieve both a scalable structural integrity amongst the few vertically-stacked graphene layers in a vertical graphene film and a desirable level of optical transparency. A structurally-integrated graphene structure is required to minimise the conductance loss at junction interfaces and to ensure sufficient mechanical stability and also to provide functionalities upon large deformation for flexible and lightweight optoelectronics and other devices' 41 .
  • the invention provides a method of preparing a free or transferrable graphene sheet comprising the steps of:
  • the proportion of (101 ) and (111 ) facets, in combination, relative to (100) facets is increased to at least 4%., and more preferably the proportion of (101 ) and (111 ) facets, in combination, relative to (100) facets is increased to at least 15%.
  • pre-treating the surface passivates the substrate surface.
  • the pre-treating is carried out for a period sufficient to hydrophilise the surface of the substrate, as determined by reduction in a water contact angle of the substrate.
  • the water contact angle of the substrate after pre-treating is for preference less than 6° more preferably even less than 3°.
  • the substrate has a surface temperature maintained solely through direct plasma heating, and it is also preferable during pre-treating that the substrate has a surface temperature maintained in the range 90-200°C.
  • the Hydrogen containing plasma is derived from Hydrogen gas alone or from a mixture of Argon and Hydrogen.
  • the Hydrogen-containing plasma is preferably derived from a 1 : 10 mixture of Argon and Hydrogen gases. It is also preferred that the mixture of Argon and Hydrogen gases is fed at 0.8 to 10 Pa.
  • pre-treating is carried out for at least 10 seconds and more preferably pre-treating is carried out for at least 30 seconds.
  • the Hydrogen-containing plasma is produced by RF power of about 100-800W.
  • the substrate has a surface temperature maintained solely by direct plasma heating, and it is also preferable during depositing graphene, that the substrate has a surface temperature maintained in the range 200-300°C.
  • the carbon source gas comprises a gas selected from the group consisting of methane, acetylene, ethylene, and fatty acid monomers. Most preferably the carbon source gas comprises methane.
  • the deposition period is 2-10 minutes.
  • the carbon source gas is fed at 1.0 to 5.0 10 Pa.
  • the plasma is produced by RF power of about 650-900W.
  • pre-treating and deposition are carried out in a continuous single process for production of transferrable graphene.
  • the polar liquid is water.
  • the invention provides a free or transferrable graphene sheet prepared by the method of the present invention.
  • the invention provides a graphene structure comprising a plurality of stacked planar carbon layers, wherein at least one layer of the structure comprises integrated horizontal and vertical nanosheet portions.
  • a portion of at least one stacked carbon layer forms a first vertical nanosheet portion, and wherein the first vertical nanosheet portion is supported by at least one second vertical nanosheet portion.
  • a portion of at least one stacked carbon layer forms a first vertical nanosheet portion, and wherein the first vertical nanosheet portion is supported by at least one second vertical nanosheet portion and wherein the first and second vertical nanosheet portions in combination with a plurality of adjacent vertical nanosheet portions form a graphene microwell.
  • the vertical nanosheet portion is connected to a horizontal nanosheet portion without an intervening junction.
  • a plurality of adjacent vertical nanosheet portions form a petal-like vertical graphene (PVG) structure in an X-Y plane, thereby to define a T-junction microwell in a X-,Y- and Z- plane.
  • PVG petal-like vertical graphene
  • the size of the microwells in X-Y plane is 1-5 ⁇ and more preferably the microwells in the X-Y plane is 1 -2 ⁇ .
  • the graphene structure comprises a plurality of microwells, and more preferably it comprises a plurality of interconnected microwells, wherein adjacent microwells have a common portion of a vertical petal-like ridge. More preferably the plurality of microwells defines a substantially regular honeycomb structure.
  • Figure 1 Illustrates a number of facets of the plasma-enabled wet-chemical-/binder-free, highly integrated 3-D vertical graphene network of the present invention:
  • Electron backscattered diffraction (EBSD) mapped images show the plane orientation in Z-direction of a polycrystalline surface of Copper substrate (foil) dominated by the (100) plane.
  • EBSD Electron backscattered diffraction
  • HG structurally-integrated horizontal graphene
  • VG vertical graphene
  • petal-like vertical graphene layers are the native curled parts of two adjacent horizontal graphene layers which eventually coalesce to each other (e) and vertically grow higher in the direction of electric field which is created by the plasma sheath.
  • the petal-like vertical graphene layers are thin (e) and thick (f) as a result of low and high methane concentration, respectively during the plasma deposition process.
  • the schematic here shows the integrated petal-like vertical graphene structure in a graphene microwell film.
  • the H 2 0 molecules intercalate and diffuse between the hydrophobic graphene microwell film and hydrophilic copper surface and decouple the film from the foil. Due to gravity, the copper foil sinks and the film is decoupled (exfoliated) from the substrate and thus floats freely in the water.
  • the white arrow mark shows the terminated graphene edge plane in the schematic of graphene microwell.
  • Figure 3 Micro-Raman spectra of graphene microwell films on a twice used copper foil, (a) after 1 st deposition process, (b) after 2nd deposition process the graphene microwell being transferred in between the deposition processes.
  • Figure 4 Schematic shows the plasma-substrate configuration inside the plasma CVD system for growth of graphene microwell films.
  • Figure 5 SEM of graphene microwell structure showing an individual salt crystal stored in the microwell.
  • FIG. 6 Comparison of the performance of two types of graphene structures useful in nano- devices.
  • GMW graphene microwell
  • PVG petal-like vertical graphene
  • a gas-sensing device made from the two different films show that the sensitivity of GMW for N0 2 gas at room temperature is almost one order of magnitude higher than for PVG films.
  • Figure 7 A schematic that shows how a graphene microwell film would be integrated into a gas- sensing platform device.
  • Figure 8 A photograph illustrating the wettability of the substrate before and after plasma activation
  • the present invention provides a plasma-enabled modification of nanoscale crystallographic features of a copper substrate surface at a substantially low temperature, 190°C or below, which not only activates the surface for deposition of a highly networked graphene film but also facilitates the instant decoupling and detachment of the film from the copper substrate when it is dipped in water (de-ionized or common tap water) at room temperature (22°C).
  • the process is carried out at low substrate temperatures, for example, 90-200°C, more usually around 190°C.
  • These relatively low plasma deposition temperatures reflect the fact that the substrate is not heated by the plasma alone, that is, there is no external heating of the substrate, since it is not required.
  • the use of such relatively low temperatures means the process is relatively mild and amenable to industrial use.
  • the schematic in Figure 1 a shows a one step, cost and energy-efficient growth process for producing high quality graphene films that can be readily released from the deposition substrate.
  • the crystal orientation of polycrystalline copper surface dominated by the presence of more than 50%, and more usually more than 90% (100) plane facets is effectively modified by its exposure to a hydrogen containing plasma, such as H 2 +Ar plasma for 90 seconds, although shorter periods, such as 30 seconds or even 10 seconds can be effective.
  • a hydrogen containing plasma such as H 2 +Ar plasma for 90 seconds, although shorter periods, such as 30 seconds or even 10 seconds can be effective.
  • the higher facets of graphene, (101 ) and (111 ) emerged on the surface of the substrate.
  • the pre-treatment plasma can be generated from hydrogen alone, but it is best to use an portion of an inert carrier gas, which will have a higher molecular weight, such as Argon, since the collision of larger molecules with the surface is believed to facilitates the changes at the surface.
  • an inert carrier gas such as Argon
  • the combination of hydrogen and an inert gas such as Argon is ideal.
  • a 1 : 10 mixture of Ar to Hydrogen is ideal, but the ratio can be higher, for example, 1 :30 Ar:H 2 .
  • Hydrogen alone the plasma will take around 30 seconds to heat the substrate and change the surface.
  • Using 1 : 10 Argon:Hydrogen will lead to a similar result in around 10 seconds.
  • the graphene is then deposited onto the copper in accordance with other known processes, in particular, graphene is applied to the modified substrate by plasma enhanced CVD, such as for example, the deposition of graphene from an CH 4 +H 2 +Ar plasma mixture.
  • plasma enhanced CVD such as for example, the deposition of graphene from an CH 4 +H 2 +Ar plasma mixture.
  • Other carbon source gases besides methane can be used for the deposition of graphene in the present invention, for instance, ethylene or monomer fatty acid can be used.
  • the deposition onto the substrate takes place directly following on from substrate pre treatment, for instance, in the same chamber immediately after pre-treatment. In this way, the pre- treatment and deposition stages are contiguous, and the entire process can be conducted continuously.
  • the deposition process is carried out without heating of the substrate, with the substrate being heated by the plasma only. Due to the slightly different nature of the deposition plasma, and the power required (650-900W) , the substrate temperature is a little higher, typically in the range of 200-300°C, however, those skilled in the art will appreciate that this is a very low temperature for graphene deposition.
  • the gases for the deposition plasma are fed at above 1.0 Pa (it is difficult to ignite the plasma below that pressure) and up to around 12 Pa, with a range of 1 -5Pa being more usual.
  • the copper foil and deposited graphene are submerged in a polar liquid such as water, preferably deionised water, whereupon the graphene instantly decouples from the foil and is detached so that it floats freely on the water ( Figure 1 b).
  • the decoupled graphene is transparent (76% transparency at an optical wavelength of 550 nm ( Figure 1 c)).
  • a number of polar liquids have been tested, such as water, ethanol and acetone, and all were found to work well.
  • the decupling process as tested in water is also very robust in relation to the conditions under which it will work. For instance, the presence of contaminants, we found to have no observable effect.
  • the decoupling works well in deionised water, tap water and even water which has been deliberately dosed with up to 0.7 M of sodium chloride.
  • the presence of calcium and lithium chloride also have no observable effect upon the decoupling.
  • tap water this being the best balance between cost and purity, it is not essential to use tap water or high quality water.
  • the free graphene film can then be transferred to any other desired sheet material .
  • Graphene could be deposited onto polymers, paper, silicon, inorganics or many other substrates.
  • the released graphene can be transferred onto a polyethylene (PET) sheet or mesoporous alumina discs.
  • the surface energy of the copper substrate is strongly influenced by the exposure to the hydrogen containing (H 2 +Ar) plasma which modifies its surface from a polycrystalline predominantly (100) surface to a passivated surface having (101 ) and (111 ) facets. This structural change is thought to effect the wetting properties.
  • the plasma pre-treatment step of the present invention the wettability of the copper surface is effectively changed from slightly hydrophobic (water contact angle ⁇ 70°) to hydrophilic (-6°) when it is exposed to a hydrogen containing (H 2 +Ar) plasma.
  • the plasma pre-treatment step is considered to be a hydrophilising step.
  • the deposited graphene film remains highly hydrophobic (contact angle -120°) ( Figure 2g) which thus facilitates its decoupling. That is, the copper surface interacts strongly with water after the deposition process, while the bottom layer of the graphene film only interacts weakly with water. As the substrate is dipped into water at room temperature, due to reverse interaction strength, water molecules are likely to intercalate and quickly diffuse between the film and copper surface (Figure 2g). This will substantially reduce the weak graphene-copper bond by the screening effect and decouple the graphene film from the copper substrate.
  • graphene films can then be readily transferred from the water onto a secondary substrate, ready for assembly into a device, sensor, or other end use applications.
  • a range of chemically diverse secondary substrates (paper, polymer, glass, ceramics) are suitable.
  • the method of the present invention avoids the use of wet chemistry or a polymeric transfer material.
  • the decoupling and transfer process of the present invention does not require either a coating of carrier material or solvent-rinsing which could damage the graphene structure.
  • the copper foil can be reused many times to produce transferable graphene films of similar quality with only minor treatment.
  • the process of the present invention is also highly energy efficient relative to alternative processes. [0071]
  • the present invention uses only 21 % of the energy of conventional thermal CVD processes and only 46% of the energy of reported plasma enhanced CVD processes.
  • the present invention provides an approach for preparing, decoupling and transferring the deposited graphene films which is instant, gentle, relatively cost-effective and environmentally friendly in terms of energy and material efficiency.
  • the pre-treatment process of the present invention allows for modification of the subsequent deposited graphene, and in particular, facilitates the formation of some novel graphene architectures.
  • the present invention also provides a scalable fabrication of a high quality highly integrated 3-D vertical graphene networks in form of graphene "microwells" on copper Cu foil in a simple, low temperature plasma based process.
  • the networks comprise high structural integration among a few vertically-stacked graphene layers and also between the horizontally and vertically orientated graphene layers without use of any passive and massive wet-chemicals or binders.
  • the graphene microwell films are not only optically transparent (76% at a wavelength of 550 nm), but also exhibit mechanical and structural integrity that remains nearly unaltered after repeated deformations.
  • the plasma process which enables the simultaneous growth and integration of a continuous horizontal graphite film and vertical petal like graphene layer in 3-5 minutes at temperature ⁇ 270°C, is at least 50% more energy efficient than previously reported plasma CVD methods.
  • the highly integrated 3-D graphene networks may be further described as comprising a plurality of horizontally stacked planar carbon layers, wherein at least one upper carbon layer is "curled up" to form a vertical nanosheet, and wherein the adjacent vertical nanosheets form a petal-like vertical graphenes (PVG) structure, thereby to define a microwell.
  • PVG petal-like vertical graphenes
  • curled up one means that the upper layer (s) protrudes upwards or could be puckered to form a vertical nanosheet.
  • the present application also allows for control over certain morphologies such as (integrated) nano-connectivity and thickness of the vertical graphene layer, properties which together provide a high density of long reactive open graphene edge planes (>0.4 km/cm 2 ) in the vertical orientation.
  • the films produced by this method comprise of integrated networks of horizontally and vertically orientated graphene layers that form during a low power, low temperature gas-plasma process using a carbon source plasma such as a obtained from a CH 4 +H 2 + Ar gas mixture, onto polycrystalline copper foils. No external heating is required and the copper surface temperature, preferably in the range of 180- 270°C, is achieved as a result of only plasma heating.
  • the plasma-assisted activation of the copper foil not only facilitates exfoliation, decoupling of the graphene, but also imparts high quality morphology to the deposited films.
  • micron/sub-micron cup-like features which are potential containers for isolating biochemical and/or chemical species such as cells, proteins, organic solutes and the like.
  • the thickness of the petal-like vertical graphene nanosheets of the present invention is controlled by the concentration of H 2 with respect to CH 4 (in terms of partial pressure) in the gas mixture of the plasma deposition process.
  • the Ar in the gas mixture also played an important role for the growth of the graphene microwell.
  • a continuous layer of horizontal graphene is compromised and the growth of petal like vertical graphene is preferred. This is possibly due to the damages at the initially deposited horizontal graphene layer film caused by excessive Ar ions bombardment, which creates a number of defect sites and the vertical graphene nanosheets eventually grow from those sites.
  • the vertical 3-D networks of the present invention are quite unique in that they provide graphene sheets which are self supported in two dimensions, yet do not have any junctions in transitioning from a horizontal plane. There is a continuous path for electrons from the horizontal to the vertical and it is seen that these graphene wells have high reactivity at the top edges of the well. [0085]
  • the vertical 3-D networks produced by the present invention remain robust during decoupling and after the transfer to chemically diverse targeted surfaces. Their high mechanical strength is attributed to their structural integrity, that is, the vertical petal-like nanosheets are simultaneously interconnected to the horizontal graphene film.
  • any shear force exerted on the film during the subsequent decoupling transfer process is likely to be distributed among the vertical inter-connections and the tendency to scroll up is thus suppressed even in the absence of any material coating. Further, the copper substrate can again be re- used for deposition of similar quality of graphene microwells.
  • the structurally robust integrated vertical 3-D can thus be readily transferred to a range of chemically diverse targeted substrates (paper, polymer, glass, etc.) without use of wet chemistry or polymeric transfer materials and retained their properties after bending several times at 1 mm radius of curvature.
  • the transferred films can also be used as sensors, particularly gas sensors, such as for nitrogen dioxide (N0 2 ) gas sensing.
  • N0 2 is a hazardous gas in the environment and continued or frequent exposure may cause increased incidences of acute respiratory illness. Therefore, its detection at trace levels is important.
  • the graphene microwell films, integrated into real nano-devices, provide high performance sensors for gas detection.
  • a scalable production of a highly integrated 3-D vertical graphene network in the form of graphene microwells on copper foils has been demonstrated in a simple, low temperature plasma-based process.
  • the networks comprise high structural integration among vertically-stacked graphene layers and the horizontally orientated layers of graphene without use of any passive and massive wet-chemicals or binders.
  • the plasma process also enables the facile decoupling of the high- quality film from the copper substrate when it is exposed to water at room temperature. This leads to a relatively cost-effective and environment-friendly transfer process.
  • graphene microwell films are not only optically transparent (76% at a wavelength of 550 nm), but also exhibit mechanical and structural integrity that is robust enough to retain its reactivity, as well as physical and electric properties after repeated deformation.
  • the production process is at least 50% more energy efficient than previously reported plasma CVD methods.
  • These films exhibit excellent sensing properties in dry environments for hazardous N0 2 gas.
  • Ar+H 2 gas mixture (ratio 1 :3) was fed into the chamber to generate the plasma at RF power and chamber pressure of 400 W and 2.5 Pa, respectively.
  • CH 4 was injected into the chamber and the RF power was increased to 680 W, while the chamber pressure was maintained at 2.5 Pa.
  • Measurement of the substrate's wettability and hence hydrophilicity was made by measuring the water contact angle of the substrate, both before and after activation.
  • the contact angle for the hydrophilic surface changes with time. This is because of the air-pockets between the water and the surface. As the air-pockets escape with time (within few minutes), the contact angle decreases rapidly due to wettability properties of the surface. However, the contact angle does not change much on the hydrophobic surface due to the surface properties.
  • the contact angle is measured after 5 minutes after a water droplet is placed on the copper surface.
  • a very high resolution camera is used to take the photo of a water-drop on copper foil and the Image J software is used to measure the contact angle.
  • Figure 8 represents a typical photograph.
  • the copper foil and deposited graphene are submerged in water, preferably deionised water at ambient temperature (22°C), upon which the graphene instantly decoupled from the foil and lifted-off onto the water surface ( Figure lb).
  • the copper foil sank.
  • the isolated graphene film resting on the water surface could then be transferred to any other desired material simply by sliding the substrate below the suspended graphene and lifting the graphene from the water.
  • the released graphene could be transferred onto a polyethylene (PET) sheet.
  • PET polyethylene
  • the graphene exhibited almost 76% transparency at an optical wavelength of 550 nm ( Figure 1 c).
  • the copper foil was re-used for several sequential experiments. Minor cleaning was required between each experiment. For example, after loading the foil into the plasma CVD chamber, the foil was first treated with hydrogen plasma at 200 W for 5 minutes to etch away any carbon left over on the foil during the transfer process.
  • Figure 3 shows the micro-Raman spectra collected from the graphene films after the use of the foil for two deposition processes, which shows a small fraction of change in peak intensity ratio and indicates almost similar quality of deposited graphene.
  • Microscopy and spectroscopy The graphene microwell films were characterised by SEM (Zeiss Auriga field emission SEM, operated at 5 kV) equipped with EBSD (NordlysNano EBSD detector, Oxford Instruments) and TEM (JEOL 3000F, operated at 300 kV). Micro-Raman spectra were collected at room temperature using a Renishaw in Via confocal Raman spectroscope (with a laser source 514 nm).
  • the intensity ratio (/ 2D /fc ) of -0.9 further confirms that the graphene microwell material is composed of a few graphene layers. There is also a disorder D-peak observed at 1352 cm "1 in the spectra which is most likely due to the presence of highly dense open graphitic edges and possibly few structural defects in the graphene layers.
  • FIG. 2a An angle-viewed scanning electron microscopy (SEM) image, Figure 2a, shows the structural integration among the vertical petal-like graphene layers in a graphene microwell film on a PET sheet after the transfer process. These inter-connected graphene layers together form micron/sub-micron cuplike features, which are potential containers for isolating biochemical and/or chemical species such as cells, proteins, etc.
  • a high-resolution SEM image ( Figure 2b) shows that these graphene layers become thinner and almost transparent towards the top edges.
  • TEM transmission electron microscopy
  • the produced graphene microwells consist of a high density of open planes (>0.4 km/cm 2 ) and, depending on their zig-zag and/or armchair 1171 configuration, they may possess localised higher density of states near Fermi-level 112 ' 171 and induce higher surface activity compared to a graphene basal plane.
  • the electron diffraction pattern ( Figure 2d) also confirms the presence of a few graphene layers in the graphene microwell film.
  • the thickness of the petal-like vertical graphene nanosheets is controlled by the concentration of H 2 with respect to CH 4 (in terms of partial pressure) in the gas mixture.
  • concentration of H 2 with respect to CH 4 in terms of partial pressure
  • the nanosheets in the vertical growth direction due to the localised directional electric field of the plasma sheath
  • H 2 concentration was >70% in gas mixture during the deposition process
  • the vertical 3-D networks remained robust during decoupling and after the transfer to chemically diverse surfaces. This is attributed to its structural integrity where vertical petal-like nanosheets are a integral part of the horizontal graphene film and are simultaneously interconnected to each other. Any shear force exerted on the film during the decoupling and transfer process is likely to be distributed among the vertical inter-connections and a tendency to scroll up is easily avoided even in the absence of the carrier material coating. Further, the copper substrate could again be used for deposition of similar- quality graphene microwells.
  • FIG. 5 shows individual salt crystals which can be stored in the cup-like structures which are formed by the petal-like vertical graphene, integrated together (dotted circle).
  • PBS solution phosphate buffered saline
  • the graphene microwell films could be used as micro-containers to store, contain and/or separate biological cells, clusters of proteins, chemicals, etc.
  • FIG. 6a shows the electrical resistance of graphene microwell electrodes compared to a non-integrated one (at a film transparency of 76%) from flat to bent at a radius of curvature of 1 mm after 10 cycles.
  • the sheet resistance of graphene microwells (-350 Ohm/cm 2 ) is relatively lower than any transferred horizontal graphene films produced in plasma CVD and comparable to horizontal graphene produced in thermal CVD processes at an elevated temperature (1000°C).
  • petal-like vertical graphene films show a relatively higher resistance of 1900 Ohm/cm 2 .
  • the sheet resistance of the films increased up to 410 and 2300 Ohm/cm 2 at a bending radius of 1 mm for graphene microwells and petal-like vertical graphenes, respectively.
  • the sheet resistance of a horizontal graphene films produced in plasma CVD systems is >1 KOhm/cm 2 due to abundance of defect sites which trap the charge carriers.
  • the vertical graphene nanosheets are deposited at the defect sites in the process, the overall sheet resistance is likely to increase due to the junction tunnelling effects.
  • the vertical petal-like nanosheets are highly integrated and constitute the bending parts of horizontal graphene layers. Therefore, this integration almost eliminates the charge carrier trapping sites in both horizontal and vertical graphene layers and reduces overall sheet resistance. This suggests that the graphene microwell films have high vertical and horizontal in-plane carrier mobilities.
  • Two separate sensing platforms were fabricated by transferring the graphene microwell and petal-like vertical graphene films onto porous anodic alumina templates (pore diameter 200 nm) and attaching two electrodes (6.0 mm apart) on each platform.
  • a chemiresistor platform was prepared by cutting a sample of the size of 5 x 3 mm 2 and attaching it to a filament holder using silver epoxy. The platform was then inserted into the sensing device which had a volume of- 60 cm 3 . Dry nitrogen was used as a buffer gas.
  • a mixture of 50 ppm N0 2 in nitrogen (Spectra Seal, BOC Limited) was further mixed with pure dry nitrogen buffer gas to obtain N0 2 concentration between 50 and 5 ppm.
  • the electrical resistivity measurements were performed using a Keithley picoammeter (model 6487) and current limit was set at 10 nA to minimise/avoid Joule heating of the sample.
  • PECVD plasma enhanced CVD
  • Microwave power 2000 W (for 2 minutes for the growth using 1000 W [ 2] ).
  • Heating system 1400 W (for 7 minutes; to heat up the substrate up to 800°C within 5 minutes and to keep the temperature for 2 minutes during the growth; it is assumed that heating unit withdraw 10 A current at 20 V).
  • the present invention uses only 79% of the energy of conventional thermal CVD processes and only 53% of the energy of reported PECVD processes.

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Abstract

L'invention concerne un procédé de préparation d'une feuille de graphène libre ou transférable comprenant le prétraitement de la surface d'un substrat de cuivre polycristallin avec un plasma contenant de l'hydrogène afin d'améliorer la proportion relative de facettes (101) et (111) par rapport à des facettes (100); à déposer du graphène sur le substrat en mettant en contact la surface du substrat avec un plasma comprenant un gaz source de carbone pendant une période de dépôt; et à découpler le graphène à partir du substrat par exposition du graphène et du substrat à un liquide polaire afin de découpler instantanément le graphène du substrat pour fournir une feuille de graphène libre ou transférable. De même, l'invention concerne une structure de graphène, comprenant une pluralité de couches de carbone planes empilées, dans laquelle au moins une couche de la structure comprend des parties nanofeuilles horizontales et verticales intégrées. La structure de graphène comprend une pluralité de micropuits interconnectés.
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EP3492428A3 (fr) * 2017-11-29 2019-09-04 Samsung Electronics Co., Ltd. Graphène nanocristallin et procédé de formation de graphène nanocristallin
CN110564087A (zh) * 2019-05-24 2019-12-13 深圳市溢鑫科技研发有限公司 一种直立型石墨烯-高分子聚合物复合材料及其制备方法
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US11217531B2 (en) 2018-07-24 2022-01-04 Samsung Electronics Co., Ltd. Interconnect structure having nanocrystalline graphene cap layer and electronic device including the interconnect structure
CN114506843A (zh) * 2022-02-25 2022-05-17 电子科技大学 一种快速在非金属基底上制备石墨烯薄膜方法
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