Method for direct deposition of graphene or graphene oxide onto a substrate of interest

Abstract

The present invention resides in a method for directly depositing graphene or graphene oxide onto a target substrate from a gaseous source of at least one carbon precursor using plasma enhanced chemical vapor deposition. The present invention also relates to a device for carrying out the method.

Description

[Technical field]

[0001] The present invention resides in a method for directly depositing graphene or graphene oxide onto a target substrate from a gaseous source of at least one carbon precursor using plasma enhanced chemical vapor deposition. The present invention also relates to a device for carrying out the method. [Background technology]

[0002] Graphene is a type of nanotube with nanowires arranged in a honeycomb lattice. 2 It is a 0.34 nm thick two-dimensional crystal made of carbon atoms. Graphene belongs to several allotropic forms of carbon, including carbon nanotubes, fullerenes or graphite. This material is characterized by high electrical conductivity (depending on its preparation method), good mechanical properties (graphene is 300 times tougher than steel of the same thickness and harder than diamond), and thermal conductivity, while being transparent. Graphene is also water and UV-resistant. This range of performance characteristics makes graphene therefore a perfect candidate for a variety of potential applications, including in the fields of nanoelectronics and microelectronics, especially field effect transistors; photovoltaic devices and organic light-emitting diodes (OLEDs), where graphene can be integrated into transparent electrodes; in the field of energy, especially as an electrode material in lithium-ion batteries or supercapacitors; in the manufacture of composites or cements based on thermoplastic or thermosetting polymers; coatings, for example to increase the flame retardancy or wear resistance of substrates; biosensors; or biopharmaceuticals. Graphene can be used in particular for the manufacture of flexible and transparent electronic components, such as touch screens.

[0003] In these applications, graphene is used as single-layer graphene on a substrate or as free-standing single-layer graphene, few-layer graphene (2-5 carbon layers), multi-layer graphene (5-10 carbon layers), graphene nanoplatelets or graphene powder. The presence of graphene is usually detected by Raman spectroscopy as sp 2This is confirmed by identifying bonded carbon or by measuring the actual number of carbon layers by atomic force microscopy (AFM).

[0004] The use of graphene oxide has also been suggested in many applications for which graphene is suitable. Graphene oxide is also a monolayer material and, unlike graphene, is hydrophilic and acts as an electrical insulator. Graphene oxide (or GrO) may be reduced to graphene-like sheets (rGrO), also known as functionalized graphene.

[0005] Among the techniques for producing graphene, chemical vapor deposition (CVD) can be mentioned. This method usually involves the reaction of CH4 and H2 at high temperatures (800-1000 ° C) to produce carbon in the gas phase, which then adsorbs on a catalyst (usually a transition metal such as nickel or copper) previously introduced in the reactor. Generally, these catalysts are in the form of metal sheets containing polycrystalline particles. Depending on the grain orientation, several Gr layers are formed on the catalyst.

[0006] One of the major drawbacks of the CVD technique is that the graphene is deposited on a catalyst, which requires an additional step of transferring the graphene thus formed onto the target substrate, for example a dielectric substrate for electronic applications. For this, a wet bench may be used to chemically attack the metal catalyst with a suitable strong acid compound. After chemical etching, the graphene thin layer is found floating on the top surface of the acid solution and is recovered with a special tool. The recovered layer is then rinsed with water before being transferred onto the target substrate. These transfer steps are obviously time consuming. Moreover, they may have a negative effect on the performance of the graphene, since they may induce contamination and structural defects.

[0007] Among CVD techniques, PECVD (standing for Plasma Enhanced Chemical Vapor Deposition) consists in replacing part of the energy of the CVD process with the energy of ionization brought about by radio frequency (RF) or microwave (MW) plasma. The high energy electrons produced by the plasma boost promote the ionization, excitation and dissociation of hydrocarbon precursors at relatively low temperatures. This technique has gained acceptance due to its ability to grow graphene directly on the desired substrate in the absence of metal catalysts.

[0008] However, attempts to grow graphene by PECVD have failed to produce graphene on catalytic substrates below 475°C (KJ. Peng et al., J. Mater. Chem., C 2013, 1, 3862) and on dielectric substrates below 450°C (D.C. Wei et al., Angew. Chem. Int. Ed. 2013, 52, 14121).

[0009] All of the above methods use methane as a carbon precursor. However, methane is a greenhouse gas and is thought to have 25 times the ability to trap heat in the atmosphere than carbon dioxide. Moreover, methane can act as a choking agent in high concentrations, requiring special precautions for its use as a reactant in an industrial environment.

[0010] It has already been suggested in US Pat. No. 9,150,418 that methane may replace various other carbon precursors, such as ethylene in the PECVD process. However, this process is generally carried out at a temperature of 800° C. FIGS. 4 and 6 of this patent describe an alternative process carried out at room temperature. In the process shown in FIG. 6, a substrate (such as copper foil or another substrate) is maintained in a low pressure environment, and then hydrogen and methane are flowed into the process chamber at room temperature, and an RF plasma is initiated, whereby graphene is said to be formed on the substrate. FIG. 4 shows a similar process in which the RF plasma is extinguished before H2 and CH4 are flowed into the process chamber. As with the prior art discussed above, these embodiments use methane as the carbon precursor. In addition, this document reveals that a carrier gas, preferably hydrogen, needs to be flowed into the process chamber along with the carbon precursor in order to form graphene and simultaneously remove copper oxide from the substrate surface. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] U.S. Patent No. 9,150,418 [Non-patent literature]

[0012] [Non-Patent Document 1] KJ. Peng et al., J. Mater. Chem., C 2013, 1, 3862 [Non-Patent Document 2] D. C. Wei et al., Angew. Chem. Int. Ed. 2013, 52, 14121 Summary of the Invention [Problem to be solved by the invention]

[0013] In this regard, there remains a need to provide a method for directly depositing graphene onto a substrate of interest under industrially and economically acceptable conditions, i.e., without the use of toxic reactants, contaminating metal catalysts and / or high temperatures. [Means for solving the problem]

[0014] The inventors have now discovered that this need may be met by replacing the methane used as the carbon precursor in the above process with ethylene in the absence of any carrier gas, thereby growing graphene at about room temperature.

[0015] The present invention therefore relates to a method for depositing graphene or graphene oxide on a substrate from a gaseous source of at least one carbon precursor using plasma enhanced chemical vapor deposition, characterized in that the carbon precursor consists of ethylene and is carried out at a temperature between 18 and 40°C in the absence of a carrier gas.

[0016] The present invention also relates to a device suitable for producing graphene or graphene oxide on a substrate, comprising: - a vessel containing a gaseous source of a carbon precursor consisting of ethylene; - a plasma reactor comprising: (a) a plasma chamber including a sample stage suitable for holding a substrate; and (b) a plasma generator including a power supply and connected to or including the plasma chamber; - a pumping device in fluid communication with the plasma chamber, the pumping device being adapted to place the plasma chamber under vacuum; - means for supplying ethylene from a container into the plasma chamber; belongs to a device that contains

[0017] The method of the present invention uses ethylene, which is a non-hazardous gas. In addition, the method is carried out at temperatures close to room temperature, thus consuming less energy and is suitable for depositing graphene on substrates that are sensitive to high temperatures. The method of the present invention can therefore be directly applied to a variety of substrates. The method further allows the omission of any pre-step of treating the substrate, for example by cleaning with plasma. Furthermore, the method of the present invention allows the production of high quality, large area graphene, for example about 15x15cm. 2 Or another 100cm 2 Or 200cm 2 It is possible to grow products of 1000 nm to 1000 nm in thickness. The device according to the invention is also cheaper than prior art devices since it does not require a furnace.

[0018] The method according to the invention involves depositing graphene or graphene oxide onto a substrate from a gaseous source of at least one carbon precursor, namely ethylene.

[0019] The substrate may be made of any material, for example selected from glass; cellulosic materials, such as paper or wood; synthetic organic materials, such as polystyrene or polyesters, in particular polyethylene terephthalate or poly(lactic acid), including poly(L-lactic acid) and poly(D,L-lactic acid); metals, preferably other than nickel and copper; metal oxides or metal carbides, such as silica, alumina or sapphire; and silicates, such as aluminum silicate and / or magnesium silicate. The substrate may be of any shape and does not have to be flat.

[0020] In the present invention, the deposition is carried out using the plasma enhanced chemical vapor deposition (PECVD) method. The plasma can be generated by direct current, microwave, or preferably radio frequency (RF) using high frequency voltage. The power supplied to the plasma is typically comprised between 150W and 400W, preferably about 300W.

[0021] The method is carried out in the absence of any gas, especially selected from hydrogen, argon, nitrogen, halogens such as chlorine, and mixtures thereof. However, the method may be followed by a single flush of oxygen of 5 sccm to 20 sccm, preferably 10 sccm, for 30 seconds to 120 seconds, preferably 60 seconds, to form graphene oxide instead of graphene. Moreover, ethylene is used as the only gas source of carbon precursor. The flow rate of the gas source may be 5 sccm to 20 sccm, preferably about 10 sccm.

[0022] As mentioned above, the method of the invention, including both deposition and the optional single flash of oxygen, is carried out at a temperature of 18-40° C., for example 20-30° C. This is typically carried out for a duration that allows the formation of the required number of graphene or graphene oxide layers, for example 2-10 seconds, preferably 5 seconds, to form a single graphene layer, and 40-80 seconds, preferably 1 minute, to form a single graphene oxide layer. Moreover, the method typically requires a concentration of 1.33×10 -5 Crowbar ~4x10 -5 Burr, preferably about 1.8x10 -5 It is carried out at a pressure of 1 bar.

[0023] After the required layer has been deposited, the ethylene flow is stopped and the substrate can then be removed from the plasma chamber.

[0024] It is therefore possible to form graphene or graphene oxide directly on a substrate in a single step. This substrate does not have to have catalytic properties but can be any substrate of interest, so that the method of the invention generally does not include a subsequent step of transferring the graphene to another substrate. Moreover, the method typically does not include any pretreatment step of the substrate, such as hydrogen or argon plasma treatment, chemical etching, physical machining, ion beam bombardment, ultrasonic cleaning, electrolytic polishing, or laser ablation. If the plasma chamber is used for purposes other than the method of the invention, the method may include a preliminary step of cleaning the plasma chamber, for example by flowing argon into the chamber, optionally in the presence of the substrate.

[0025] The invention also resides in a device suitable for carrying out the above method. The device thus comprises a vessel containing a gaseous source of carbon precursor consisting of ethylene. The vessel is in fluid communication with a plasma reactor, which comprises a plasma generator and a plasma chamber comprising a sample stage suitable for holding a substrate. Means are provided for feeding ethylene from the vessel into the plasma chamber. If graphene oxide has to be formed, the device of the invention may further comprise means for introducing oxygen into the plasma chamber. A mass flow controller may be provided for controlling the flow of the gas source. The device of the invention further comprises a pumping device suitable for placing the plasma chamber under vacuum. The vacuum line connecting the pumping device and the plasma chamber may be equipped with one or more pressure gauges and optionally one or more vacuum control valves. The plasma chamber may be in the form of a tube and is usually made of quartz, alumina, glass or any other non-reactive material. According to an embodiment of the invention, the device may further comprise means for tilting, oscillating or rotating the sample stage in the plasma chamber, so that some or all sides of the substrate can be coated with graphene or graphene oxide. Moreover, to control the graphene formation, the plasma chamber can be interfaced with an optical device, in particular an optical spectrometer connected to the plasma chamber using a fiber optic cable. Alternatively or additionally, the plasma chamber may be interfaced with a mass spectrometer to detect and analyze by-products such as hydrogen produced during graphene formation.

[0026] Finally, the plasma chamber typically includes a means for venting gases (such as hydrogen produced during graphene formation) out of the plasma chamber.

[0027] The plasma chamber is connected to or at least partially contained within a plasma generator that includes a power source, which may be selected from direct current, microwave and radio frequency generating systems, preferably radio frequency generating systems, more preferably capacitively coupled radio frequency. [Brief description of the drawings]

[0028] [Figure 1] FIG. 1 is a diagram showing an X-ray diffraction pattern of Gr obtained according to the present invention. [Diagram 2] FIG. 1 represents an X-ray diffraction diagram of GrO obtained according to the present invention. [Diagram 3] FIG. 2 shows the Raman spectrum of Gr deposited on a silicon substrate according to the present invention. [Figure 4] FIG. 2 is a Raman spectrum of Gr deposited on a glass substrate according to the present invention showing vibrational modes. [Diagram 5] FIG. 1 depicts a Raman spectrum of GrO deposited on a glass substrate in accordance with the present invention, showing vibrational modes. [Figure 6] FIG. 1 shows the optical absorbance of Gr deposited on a quartz substrate in the range of 200 to 800 nm. [Figure 7] FIG. 13 shows the electrical resistivity of graphene (voltage sweep + / - 0.3 V). [Figure 8] FIG. 13 shows the variation in work function of films made of graphene layers of various thicknesses (1-4 layers) compared to the uncoated Si substrate used in this experiment. [Figure 9] FIG. 9A shows the variation in current of a graphene film depending on its thickness (1 to 4 layers), and FIG. 9B shows the variation in resistance of a graphene film depending on its thickness (1 to 4 layers). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] The present invention will be better understood in light of the following examples, which are presented for illustrative purposes only and are not intended to limit the scope of the invention, which is defined by the appended claims. EXAMPLES

[0030] Example 1 Preparation of graphene and graphene oxide films A standard capacitive plasma PECVD device with a custom processing chamber was used. The power of the plasma reactor was 300 W, and the pressure in the chamber was kept at 10 -5 Ethylene gas was introduced into the chamber containing the glass substrate at a flow of 10 sccm for 5 seconds or more depending on the number of layers of Gr desired to be produced.

[0031] To generate GrO, a single flush of oxygen was performed at 10 sccm for 60 seconds before carrying out the above steps.

[0032] Example 2 Analysis and characterization of graphene and graphene oxide films The Gr and GrO obtained according to Example 1 were analyzed to confirm their crystal structures.

[0033] Various experiments were further carried out to determine the properties of as-grown graphene and graphene oxide, and where necessary, the method of Example 1 was reproduced directly on the substrates used in these experiments.

[0034] XRD analysis: X-ray diffraction patterns of as-grown graphene were obtained using a high-resolution D8 Discover Bruker diffractometer (Cu K アルファ Radiation was performed at 0.154 nm in 2-theta rocking mode over a range of 5° to 90°.

[0035] As shown in Figures 1 and 2, Gr and GrO grown by PECVD according to the present invention generally exhibited the same crystal structure as described in the literature.

[0036] Raman spectroscopy: Raman spectra of as-grown graphene were recorded at room temperature using a micro-Raman Renishaw spectrometer equipped with a CCD detector. A green laser was used for excitation (532 nm). The recorded spectra were measured at 1000 cm with a laser power of 0.8 mW and an exposure time of 20 s for 5 accumulations. -1 ~3500cm -1was obtained from.

[0037] As shown in Figures 3-5, Gr and GrO grown by PECVD according to the present invention showed the same spectra as those generally described in the literature. The presence of the typical oscillations of Gr and GrO is a sign of successful fabrication. The two shades were separated according to the optimized sequence.

[0038] UV-VIS Near IR: The optical properties of the as-grown graphene were obtained using a UV-visible-near-infrared spectrophotometer JASCO V-670 equipped with a monochromator operating in the spectral range 200–1500 nm with 2 nm steps in both reflection and transmission modes.

[0039] FIG. 6 shows the transmittance recorded for the PECVD monolayer Gr of the present invention, which appears to be similar to that reported in the literature, particularly the 270-300 nm transition observed in the optical behavior.

[0040] Electrical measurements: Electrical measurements were carried out at room temperature on the as-grown graphene using a Solartron Impedance analyzer SI-12060.

[0041] + / - 8 volts were applied and the resulting current was measured using two probes.

[0042] Electrical measurements performed on the PECVD glass obtained according to the present invention showed resistivities (approximately 6KΩ) similar to those obtained with the few-layer CVD glass. -1 ) is shown.

[0043] Graphene work function measurement: A scanning probe based technique, the so-called Kelvin Probe Force Microscopy (KPFM), was used to measure the work function of the graphene layers. This method allows the measurement of the work function of the sample with a spatial resolution down to the 5 nm level. To confirm the intrinsic nanoscale electronic properties of the graphene produced according to the invention, films of different thicknesses were prepared on insulating Si substrates. As can be seen in Figure 8, the work function of the graphene layers was measured as a function of the number of layers.

[0044] The work function of pristine graphene shows a 300 meV increase compared to the bare Si substrate. Interestingly, the work function values ​​for films of different thicknesses are somehow stable around the average value of about 4.65 eV. This value approaches that of bulk graphite. This observation is in contrast to the graphene layers reported in the available literature, which are usually prepared by mechanical exfoliation, epitaxy on SiC or CVD. For these latter types of graphene, the work function has been observed to increase or decrease with the number of layers depending on the underlying substrate. Those variations were explained by the interfacial transfer of charges between the substrate and the graphene. The relatively stable values ​​of the work function of our graphene films for all film thicknesses indicate a higher quality of the interface in this case.

[0045] Measuring the resistance of graphene at the nanoscale: Measuring the conductivity (or resistance) at the nanoscale is done using the so-called current-sensing atomic force microscope (C-AFM). This method uses a nanometer current-sensing AFM probe as a scanning electrode connected to a current amplifier and measures the current flowing through the layer (vertically or laterally, depending on the experimental connection to the back electrode) by applying a voltage difference between the AFM tip and the back electrode.

[0046] The current and resistance of graphene films according to the present invention with different thicknesses (1LG to 4LG) were measured, and the results are reported in FIG. 9 (FIG. 9A and FIG. 9B).

[0047] As can be seen from these figures, the resistance of the graphene film is reduced by about an order of magnitude for 2LG compared to 1LG and Si substrate, making thicker graphene films advantageous for in-plane conductive applications.

Claims

1. 1. A method for depositing graphene or graphene oxide onto a substrate from a gaseous source of at least one carbon precursor using plasma-enhanced chemical vapor deposition, comprising: The method is characterized in that the carbon precursor comprises ethylene and is carried out at a temperature of 18-40°C in the absence of a carrier gas.

2. 2. The method according to claim 1, characterized in that the substrate is made of a material selected from glass; cellulosic materials, such as paper or wood; synthetic organic materials, such as polystyrene or polyester, in particular polyethylene terephthalate or poly(lactic acid); metals; metal oxides or metal carbides, such as silica, alumina or sapphire; and silicates, such as aluminum silicate and / or magnesium silicate.

3. 3. The method of claim 1 or 2, which does not include a subsequent step of transferring the graphene to another substrate.

4. 2. The method of claim 1, wherein the plasma enhanced chemical vapor deposition is performed after a single flash of oxygen to form graphene oxide.

5. 2. The method of claim 1, wherein the flow rate of ethylene is between 5 sccm and 20 sccm.

6. 10. The method of claim 1, wherein the method is carried out for a duration that allows for the formation of a required number of graphene or graphene oxide layers, such as 2 seconds to 10 seconds to form a single graphene layer, or 40 seconds to 80 seconds to form a single graphene oxide layer.

7. 10. The method of claim 1, carried out at a temperature of 20 to 30°C.

8. 1.33x10 -5 Crowbar ~ 4x10 -5 10. The method of claim 1, carried out at a pressure of 1 bar.

9. 2. The method according to claim 1, wherein the power supplied to the plasma is between 150W and 400W.

10. 1. A device suitable for producing graphene or graphene oxide on a substrate, comprising: - a vessel containing a gaseous source of a carbon precursor consisting of ethylene; - a plasma reactor comprising: (a) a plasma chamber including a sample stage suitable for holding a substrate; and (b) a plasma generator including a power supply and connected to or including the plasma chamber; - a pumping device in fluid communication with the plasma chamber, the pumping device being suitable for placing the plasma chamber under vacuum; - means for supplying ethylene from the container into the plasma chamber; Including, the device.

11. 11. The device of claim 10, including means for tilting, oscillating or rotating the sample stage within the plasma chamber.

12. 12. Device according to claim 10 or 11, characterized in that the power source is selected from systems generating direct current, microwaves and radio frequencies.

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