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

Abstract

The present invention pertains to a process for direct deposition of graphene oxide onto a substrate of interest from a gaseous source of at least one carbon precursor, using a plasma-enhanced chemical vapor deposition method. It is also directed to a device for implementing this process.

Claims

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

2. The process according to claim 1, characterized in that the substrate is made of a material selected from: glass; cellulosic materials; synthetic organic materials; a metal; a metal oxide or a metal carbide; and a silicate.

3. The process according to claim 2, characterized in that the cellulosic materials are paper or wood; the synthetic organic material is a polystyrene, a polyester, polyethylene terephthalate or poly(lactic acid); the metal is a metal other than nickel or copper; the metal oxide or metal carbide is a silica, alumina or sapphire; and the silicate is aluminum silicate or magnesium silicate.

4. The process according to claim 1, which does not include a subsequent step of transferring the graphene to another substrate.

5. The process according to claim 1, characterized in that said plasma-enhanced chemical vapor deposition is performed after a single flash of oxygen to form graphene oxide.

6. The process according to claim 1, characterized in that the flow rate of the ethylene is between 5 sccm and 20 sccm.

7. The process according to claim 1, which is performed for a duration allowing the formation of the required number of graphene or graphene oxide layers.

8. The process according to claim 7, wherein the duration is 2 seconds to 10 seconds for forming a single graphene layer and 40 seconds to 80 seconds for forming a single graphene oxide layer.

9. The process according to claim 1, which is carried out at a temperature between 2 and 30 C.

10. The process according to claim 1, which is carried out at a pressure of between 1.3310.sup.5 bar and 410.sup.5 bar.

11. The process according to claim 10, wherein the pressure is about 1.810.sup.5 bar.

12. The process according to claim 1, characterized in that the power provided to the plasma is between 150 W and 400 W.

13. The process according to claim 12, wherein the power provided to the plasma is about 300 W.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1 and 2 represent the X-Ray Diffraction pattern of Gr and GrO, respectively, as obtained according to this invention.

(2) FIG. 3 represents the Raman spectra of Gr deposited on silicon substrate according to this invention.

(3) FIGS. 4 and 5 represent the Raman spectra of Gr and GrO deposited on glass substrate according to this invention, showing the vibration modes.

(4) FIG. 6 shows the optical absorbance of Gr deposited on quartz substrate in the range of 200-800 nm.

(5) FIG. 7 represents the electrical resistivity of graphene (voltage sweep+/0.3 V).

(6) FIG. 8 shows the variation in the work function of a film made of layers of graphene of various thicknesses (between 1 and 4 layers), compared to the uncovered Si substrate used in this experiment.

(7) FIGS. 9A and 9B show the variation of current and resistance of graphene films, respectively, depending on their thickness (between 1 and 4 layers).

EXAMPLES

(8) This invention will be better understood in light of the following examples which are given for illustrative purposes only and do not intend to limit the scope of the invention, which is defined by the attached claims.

Example 1: Preparation of Graphene and Graphene Oxide Films

(9) A standard capacitive plasma PECVD device provided with a custom processing chamber was used. The power of the plasma reactor was 300 W and the pressure inside the chamber was set to 10.sup.5 bar. Ethylene gas was introduced into the chamber, which contained a glass substrate, with a flow of 10 sccm for 5 seconds or more, depending on the number of desired layers of Gr to be produced.

(10) In order to produce GrO, a single flash of oxygen at 10 sccm for 60 seconds is performed before conducting the above steps.

Example 2: Analysis and Properties of Graphene and Graphene Oxide Films

(11) The Gr and GrO obtained according to Example 1 were analyzed to confirm their crystal structure.

(12) Various experiments were further performed to measure the properties of the as-grown graphene and graphene oxide. When needed, the method of Example 1 was reproduced directly on the substrate used in these experiments.

(13) XRD Analysis:

(14) X-ray diffraction patterns of as-grown graphene were carried out on a high resolution D8 Discover Bruker diffractometer (Cu K.sub.alpha radiation, 0.154 nm) in rocking 2 teta mode in the range of 5-90.

(15) As shown on FIGS. 1 and 2, the Gr and GrO grown by PECVD according to this invention exhibited the same crystal structure as commonly described in the literature.

(16) Raman Spectroscopy:

(17) The Raman spectra of as-grown graphene were recorded at room temperature using a micro-Raman Renishaw spectrometer equipped with a CCD detector. The green laser was used for the excitation (532 nm). The recorded spectra were obtained from 1000 cm.sup.1 to 3500 cm.sup.1 at seconds exposure time at 0.8 mW laser power integration 5.

(18) As shown on FIGS. 3 to 5, the Gr and GrO grown by PECVD according to this invention exhibited the same spectra as commonly described in the literature. The presence of the typical vibrations of Gr and GrO is the signature of the successful fabrication. An optimization sequence was followed to develop the two shades separately.

(19) UV-VIS Near IR:

(20) The optical properties of as-grown graphene were obtained using UV-Visible-near InfraRed spectrophotometer JASCO V-670 equipped with a monochromator operating in the spectra range 200-1500 nm at 2 nm step in both reflective and transmission modes.

(21) FIG. 6 shows the transmittance recorded in the PECVD single-layer Gr of this invention which appears to be similar to that reported in the literature, especially the 270-300 nm transition observed in optical behavior.

(22) Electrical Measurements:

(23) The electric measurements were carried out at room temperature on as-grown graphene using a Solartron Impedance analyzer SI-12060.

(24) +/8 Volts were applied and the generated currents were measured using 2 probes.

(25) The electrical measurements performed on the PECVD Gr obtained according to this invention indicate a resistivity (6 K.sup.1) of the same order of magnitude of the one obtained on few-layers CVD Gr.

(26) Measurement of the Graphene Work Function:

(27) The work function of graphene layers was measured using a scanning probe-based technique so-called Kelvin probe force microscopy (KPFM). This method allows the measurement of a sample's work function with a spatial resolution down to the 5 nm level. To identify the intrinsic nanoscale electronic properties of graphene manufactured according to this invention, films of various thicknesses were prepared on an insulating Si substrate. The work function of graphene layers has been measured depending on the number of layers, as seen in FIG. 8.

(28) The work function of the as-graphene shows a 300 meV increase compared to the bare Si substrate. Interestingly, the value of the work function for the films of different thicknesses is somehow stable around a mean value of about 4.65 eV. This value approaches that of the bulk graphite. This observation contrasts with the graphene layers reported in the available literature usually prepared via mechanical exfoliation, epitaxy on SiC or CVD. For these latter types of graphene, the work function has been observed to either increase or decrease with the number of layers depending on the underlying substrate. Those variations were explained by an interfacial transfer of charge between the substrate and the graphene. The relatively stable value of the work function of our graphene films for all films thickness points towards a higher quality of the interface in this case.

(29) Measurement of the Resistance of Graphene at Nano-Scale:

(30) Measuring the conductivity (or resistance) at the nanoscale is performed using a so-called conductive atomic force microscopy (C-AFM). This method used a nanometric conductive AFM probe as scanning electrode connected to a current amplifier, that measured currents flowing through layers (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. The current and resistance of graphene films according to this invention with different thicknesses (1LG to 4LG) were measured, and the results are reported in FIGS. 9A and 9B. As it can be seen from these Figures, the resistance of the graphene films undergoes a decrease of almost one order of magnitude for 2 LG compared to the 1 LG and Si substrate, making thicker graphene films more favorable for in-plane conductivity applications.