3D GRAPHENE

Abstract

A method of forming a 3D graphene material adhered to a surface of a substrate comprises: providing a carbon source on the surface of the substrate; and exposing at least a portion of the carbon source and/or at least a portion of the substrate to a laser beam, thereby converting at least a portion of the carbon source into a 3D graphene material adhered to the surface of the substrate.

Claims

1. A method of forming a 3D graphene material adhered to a surface of a substrate, the method comprising: providing a carbon source on the surface of the substrate, the carbon source comprising carbon-containing material; and exposing at least a portion of the carbon source and/or at least a portion of the substrate to a laser beam, thereby converting at least a portion of the carbon source into a 3D graphene material adhered to the surface of the substrate.

2. The method according to claim 1, wherein the carbon source is a preformed sheet comprising carbon-containing material and wherein converting at least a portion of the carbon source into the 3D graphene material adhered to the surface of the substrate comprises transferring carbon from the preformed sheet to the surface of the substrate and forming a 3D graphene material adhered to the surface of the substrate.

3. The method according to claim 1, further comprising removing one or more unconverted portions of the carbon source which have not converted to the 3D graphene material from the surface of the substrate.

4. The method according to claim 1, wherein the carbon source comprises one or more polymers.

5. The method according to claim 1, wherein the substrate comprises one or more materials which are substantially transparent to the laser beam.

6. The method according to claim 1, wherein the substrate absorbs greater than 60% of incident light from the laser beam at the wavelength or wavelengths of the laser beam.

7. The method according to claim 1, wherein the substrate comprises one or more of the following: silicon, silicon dioxide, gallium nitride, gallium arsenide, zinc oxide.

8. The method according to claim 1, wherein the substrate comprises one or more polymers.

9. The method according to claim 1, wherein the laser beam is a pulsed laser beam.

10. The method according to claim 1, further comprising introducing one or more dopants into the 3D graphene material formed and adhered to the substrate.

11. The method according to claim 1, wherein the method is carried out at atmospheric pressure and at room temperature.

12. A system comprising a 3D graphene material adhered to a substrate, the 3D graphene material having been formed by the method according to claim 1.

13. Use of the method according to claim 1 in the manufacture of one or more device components.

14. A device component incorporating the system according to claim 12.

15. A 3D graphene material comprising oxygen at an atomic percentage of less than 3% and/or nitrogen at an atomic percentage of less than 3%.

16. A device component manufactured by the method according to claim 13.

Description

DESCRIPTION OF THE DRAWINGS

[0080] An example embodiment of the present invention will now be illustrated with reference to the following Figures in which:

[0081] FIG. 1 shows a polyimide film in contact with a silicon substrate, located beneath a CO.sub.2 pulsed laser engraving system, prior to laser treatment;

[0082] FIG. 2 shows the polyimide film and silicon substrate of FIG. 1 during laser treatment;

[0083] FIG. 3 shows the polyimide film and silicon substrate of FIG. 1 following laser treatment;

[0084] FIG. 4 shows the silicon substrate of FIG. 1 after removal of the polyimide film following laser treatment;

[0085] FIG. 5 shows a Raman spectrum measured for 3D graphene deposited on a silicon substrate using the method shown in FIGS. 1 to 4;

[0086] FIG. 6 shows an X-ray photoelectron spectrum for 3D graphene deposited on a silicon substrate using the method shown in FIGS. 1 to 4;

[0087] FIG. 7 shows a polyimide film in contact with a polystyrene substrate, located beneath a CO.sub.2 pulsed laser engraving system, prior to laser treatment;

[0088] FIG. 8 shows the polyimide film and polystyrene substrate of FIG. 7 during laser treatment;

[0089] FIG. 9 shows the polyimide film and polystyrene substrate of FIG. 7 following laser treatment;

[0090] FIG. 10 shows the polystyrene substrate of FIG. 7 after removal of the polyimide film following laser treatment;

[0091] FIG. 11 shows a Raman spectrum measured for 3D graphene deposited on a polystyrene substrate using the method shown in FIGS. 7 to 10; and

[0092] FIG. 12 shows an AFM image of a 3D graphene film deposited on a polyimide substrate.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

First Example Embodiment

[0093] 3D graphene was deposited on and adhered to a silicon substrate by the method set out below and as illustrated in FIGS. 1 to 4. A 600 m thick silicon substrate 1 was placed directly on top of a 120 m thick polyimide film, as shown in FIG. 1.

[0094] A CO.sub.2 infrared pulsed laser engraving and cutting system (the Trotec Speedy 400 flexx) 3 was used to direct a laser beam 4 at a surface of the substrate facing away from the polyimide film, as shown in FIG. 2. The laser system was tuned to emit light at a wavelength of 10.6 m, with a beam size of 50 m, a pulse duration of 14 s and a power of 14.14 W. The laser beam was scanned across the surface of the substrate at a scan rate of 284 mm/s. The process was carried out at room temperature and at atmospheric pressure.

[0095] As shown in FIG. 2, a portion 5 of the polyimide film, immediately adjacent to the region of the substrate at which the laser beam was directed, was converted into 3D graphene. Without intending to be bound by theory, the inventors believe that heat (and/or light) generated by the laser was transmitted through the substrate (indicated by dashed line 6 in FIG. 2) to the interface 7 between the substrate and the polyimide film, such that the temperature of the polyimide film was raised locally to between 800 C. and 1030 C., at which temperature the polyimide film converted to 3D graphene.

[0096] The polyimide film was converted to 3D graphene at the interface 7. The 3D graphene formed did not extend through the full thickness of the polyimide film.

[0097] The laser beam was switched off (FIG. 3) and unconverted portions of the polyimide film were removed from the substrate (FIG. 4). The inventors found that a portion 5A of the 3D graphene which had been formed from the polyimide film remained adhered to the substrate when the unconverted portions of the polyimide film were removed. The remainder 5B of the 3D graphene remained adhered to the polyimide film.

[0098] On further inspection, the inventors found that the structure of the silicon substrate at the interface between the substrate and the 3D graphene had been modified. There are indications that a thin layer of what is believed to be silicon carbide (SiC) or silicon oxycarbide (SiO.sub.xC.sub.y) had been formed at the interface between the silicon substrate and the 3D graphene, bonding the 3D graphene to the silicon substrate.

[0099] The 3D graphene deposited on the silicon substrate was characterised using Raman spectroscopy and X-ray photoelectron spectroscopy (XPS).

[0100] The Raman spectrum shown in FIG. 5 has three principal peaks characteristic of 3D graphene. In particular, the D peak at 1344 cm.sup.1 is characteristic of the presence of lattice defects and bent sp.sup.2 carbon-carbon bonds and the G peak at 1577 cm.sup.1 is characteristic of sp.sup.2 carbon hybridisation, with the presence of distorted six-fold carbon rings, or carbon rings of other orders, and with an upper limit of 5% sp.sup.a carbon hybridisation. The 2D peak at 2685 cm.sup.1 is characteristic of second order transitions in the 3D graphene and the absence of a doublet structure here indicates a lack of planar AB stacking which would be found in multilayer 2D graphene or graphite. Fitting the 2D peak with a single Lorentzian peak (having a full width at half maximum of 67 cm.sup.1) centred at 2685 cm.sup.1 indicates that there are only one, or a few, graphene-like layers present in the 3D graphene formed. Analysis of the D/G peak ratio (0.4) indicates that the average grain size (i.e. the 3D graphene crystallite size) was 43.6 nm.

[0101] The XPS spectrum shown in FIG. 6 has a dominant peak at 284.5 eV, which indicates the presence of sp.sup.2 carbon-carbon bonds. The peaks associated with carbon-nitrogen single and double bonds, as well as carbon-oxygen single and double bonds, are small. The XPS analysis indicates that 96% of the atoms present are carbon atoms, while only 2.8% of the atoms present are nitrogen atoms and only 1.2% of the atoms present are oxygen atoms.

[0102] The 3D graphene formed by this method was found to be between 5 m and 20 m thick. The 3D graphene was found to be porous with an average pore size of between 4 nm and 10 nm.

[0103] The method according to this first example embodiment of the invention has also been used to form 3D graphene on a silicon dioxide wafer (consisting of a 300 nm thick layer of silicon dioxide on top of a silicon wafer) with similar results. 3D graphene materials deposited using the method according to this first example embodiment have been doped with boron and with nitrogen using standard doping methods known in the field, including plasma doping.

Second Example Embodiment

[0104] 3D graphene was deposited on and adhered to a polystyrene substrate by the method set out below and as illustrated in FIGS. 7 to 10. A 25 m thick polyimide film 8 was placed directly on top of a 600 m thick polystyrene substrate 9, as shown in FIG. 7.

[0105] A CO.sub.2 infrared pulsed laser engraving and cutting system (the Trotec Speedy 400 flexx) 10 was used to direct a laser beam 11 at a surface of the polyimide film 8 facing away from the substrate 9, as shown in FIG. 8. The laser system was tuned to emit light at a wavelength of 10.6 m, with a beam size of 50 m, a pulse duration of 14 s and a power of 6 W. The laser beam was scanned across the surface of the substrate at a scan rate of 87.5 mm/s. The process was carried out at room temperature and at atmospheric pressure.

[0106] As shown in FIG. 8, a portion 12 of the polyimide film, at which the laser beam was directed, was converted into 3D graphene. The full thickness of the polyimide film was converted into 3D graphene.

[0107] The laser beam was switched off (FIG. 9) and unconverted portions of the polyimide film were removed from the substrate (FIG. 10). The inventors found that the 3D graphene which had been formed from the polyimide film remained adhered to the substrate when the unconverted portions of the polyimide film were removed. On further inspection, the inventors found that the structure of the polystyrene substrate at the interface between the substrate and the 3D graphene had been modified. There are indications that a thin layer of the polystyrene substrate at the interface had melted and resolidified, bonding the 3D graphene to the substrate.

[0108] The 3D graphene deposited on the polystyrene substrate was characterised using Raman spectroscopy.

[0109] The Raman spectrum shown in FIG. 5 has three principal peaks characteristic of 3D graphene. In particular, the D peak at 1340 cm.sup.1 is characteristic of the presence of lattice defects and bent sp.sup.2 carbon-carbon bonds and the G peak at 1577 cm.sup.1 is characteristic of sp.sup.2 carbon hybridisation, with the presence of distorted six-fold carbon rings, or carbon rings of other orders, and with an upper limit of 5% sp.sup.a carbon hybridisation. The 2D peak at 2680 cm.sup.1 is characteristic of second order transitions in the 3D graphene and the absence of a doublet structure here indicates a lack of planar AB stacking which would be found in multilayer 2D graphene or graphite. Fitting the 2D peak with a single Lorentzian peak (having a full width at half maximum of 61 cm.sup.1) centred at 2680 cm.sup.1 indicates that there are only one, or a few, graphene-like layers present in the 3D graphene formed. Analysis of the D/G peak ratio (0.8) indicates that the average grain size (i.e. the 3D graphene crystallite size) was 23.5 nm.

[0110] The 3D graphene layer formed by this method was found to be between 20 m and 45 m thick. The electrical conductivity of the 3D graphene, as determined by galvanic impedance measurements, was found to be between 10 S/cm and 100 S/cm. The 3D graphene was found to be porous with an average pore size of between 4 nm and 10 nm.

[0111] The method according to this second example embodiment of the invention has also been used to form 3D graphene on substrates consisting of (1) a thin film of cyclic olefin copolymer (COC) and (2) a thin film of poly(methylmethacrylate) (PMMA), with similar results.

[0112] FIG. 12 is an atomic force microscopy (AFM) image which provides an example of the finely detailed 3D graphene structures which can be deposited by this method.

[0113] 3D graphene materials deposited using the method according to this first example embodiment have been doped with boron and with nitrogen using standard doping methods known in the field, including plasma doping.

[0114] Further variations and modifications may be made within the scope of the invention herein disclosed.