SP3-BONDED CARBON MATERIALS, METHODS OF MANUFACTURING AND USES THEREOF

Abstract

The present invention provides an ultrathin and crystalline sp3-bonded carbon sheet, a stack structure, heterostructure and composite material comprising said ultrathin and crystalline sp3-bonded carbon sheet, and a method of manufacture of ultrathin and crystalline sp3-bonded carbon sheets. The method comprises the steps of providing a few-layer graphene starting material, disposing the few-layer graphene starting material on a substrate within a chemical vapour deposition chamber comprising a vacuum chamber and a feed gas inlet, and flowing a feed gas comprising hydrogen over the substrate at a substrate temperature of 325 C. or less and a pressure of 100 Torr or less to at least partially convert the few-layer graphene starting material into ultrathin and crystalline sp3-bonded carbon sheets. The method according to the present invention is the first method for successful production of ultrathin and crystalline sp3-bonded carbon sheets, including e.g. lonsdaleite sheets and diamond sheets. Advantageously it may also be relatively low cost, low waste, may avoid the use of complex apparatus having multiple components, and may allow operation under mild processing conditions.

Claims

1. An ultrathin and crystalline sp.sup.3-bonded carbon sheet.

2. The ultrathin and crystalline sp.sup.3-bonded carbon sheet according to claim 1 comprising 2 to 10 atomic layers of sp.sup.3-bonded carbon.

3. The ultrathin and crystalline sp.sup.3-bonded carbon sheet according to claim 1 wherein the sheet has a maximum thickness of 22 .

4. The ultrathin and crystalline sp.sup.3-bonded carbon sheet according to claim 1 wherein at least a portion of the sheet has a structure selected from: lonsdaleite, diamond, or another diamond polytype, or a combination of two or more of these structures.

5. The ultrathin and crystalline sp.sup.3-bonded carbon sheet according to claim 1 wherein the sheet is electronically doped.

6. A structure comprising one or more ultrathin and crystalline sp.sup.3-bonded carbon sheets, wherein the structure is selected from the group consisting of: a stack structure; a heterostructure further comprising graphene; and a composite material further comprising a matrix material.

7. (canceled)

8. The structure according to claim 6 wherein the structure is a stack structure further comprising a material selected from: a one-dimensional material, a two-dimensional material, nanotubes, or nanowires.

9.-10. (canceled)

11. The structure according to claim 6, wherein the structure is a composite material, and wherein the matrix material comprises a polymer, a semiconductor, a ceramic, a metal, or combinations thereof.

12. A method of manufacture of ultrathin and crystalline sp.sup.3-bonded carbon sheets comprising the steps of: providing a few-layer graphene starting material; disposing the few-layer graphene starting material on a substrate within a chemical vapour deposition chamber comprising a vacuum chamber and a feed gas inlet; and flowing a feed gas comprising hydrogen over the substrate at a substrate temperature of 325 C. or less and a pressure of 100 Torr or less to at least partially convert the few-layer graphene starting material into ultrathin and crystalline sp.sup.3-bonded carbon sheets.

13. The method of manufacture of ultrathin and crystalline sp.sup.3-bonded carbon sheets according to claim 12 wherein the few-layer graphene starting material comprises 2-10 atomic layer graphene sheets

14. The method of manufacture of ultrathin and crystalline sp.sup.3-bonded carbon sheets according to claim 12 wherein the substrate temperature is from 325 to 170 C.

15. The method of manufacture of ultrathin and crystalline sp.sup.3-bonded carbon sheets according to claim 12 wherein the step of flowing the feed gas is performed at a pressure from 5 to 100 Torr.

16. The method of manufacture of ultrathin and crystalline sp.sup.3-bonded carbon sheets according to claim 12 comprising the step of flowing an additional feed gas over the substrate.

17. The method of manufacture of ultrathin and crystalline sp.sup.3-bonded carbon sheets according to claim 12 wherein the feed gas(es) comprise a gas selected from: PH.sub.4, B.sub.2H.sub.6, BH.sub.3, SF.sub.6, F.sub.2, Br.sub.2, N.sub.2, H.sub.2S, NH.sub.4, B.sub.3N.sub.3H.sub.6, Ar, He.

18. The method of manufacture of ultrathin and crystalline sp.sup.3-bonded carbon sheets according to claim 12 wherein hydrogen gas is the sole feed gas.

19. The method of manufacture of ultrathin and crystalline sp.sup.3-bonded carbon sheets according to claim 12 further comprising the step of providing an additional solid source.

20. The method of manufacture of ultrathin and crystalline sp.sup.3-bonded carbon sheets according to claim 12, wherein the chemical vapor deposition chamber comprises a filament, and the filament is heated as the feed gas is flowed over the substrate to promote thermal decomposition of the feed gas.

21. The method of manufacture of ultrathin and crystalline sp.sup.3-bonded carbon sheets according to claim 20 wherein the filament comprises a material selected from the group consisting of tungsten, rhenium, tantalum and platinum.

22. The method of manufacture of ultrathin and crystalline sp.sup.3-bonded carbon sheets according to claim 12 wherein the step of flowing feed gas over the substrate is performed for a time of 6 minutes to 8 hours.

23.-25. (canceled)

Description

SUMMARY OF THE FIGURES

[0061] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0062] FIG. 1 shows a schematic of a hot-filament chemical vapour deposition (HFCVD) system as used in one method according to the present invention.

[0063] FIG. 2 shows exemplary FTIR-ATR microscopy image processed on the integrated intensity of CH stretching band, of few-layer graphene converted into ultrathin and crystalline sp.sup.3-carbon sheets according to the present invention.

[0064] FIG. 3 shows exemplary absorbance FTIR spectra taken in the region identified by a white arrow in FIG. 2.

[0065] FIGS. 4-8 show UV Raman spectra of different regions of an embodiment of the invention formed by conversion of few-layer graphene.

[0066] FIG. 4 shows a UV Raman spectrum of lonsdaleite sheets elaborated from the conversion of few-layer graphene according to the present invention (excitation wavelength of 244 nm). The lonsdaleite peak is centred at around 1323.1 cm.sup.1.

[0067] FIG. 5 shows a UV Raman spectrum of graphenelonsdaleite sheets stack structure elaborated from the conversion of few-layer graphene at low few-layer graphene temperature according to the present invention (excitation wavelength of 244 nm). The lonsdaleite peak is centred at around 1323.3 cm.sup.1.

[0068] FIG. 6 shows a UV Raman spectrum of a graphenelonsdaleite sheet stack structure elaborated from the conversion of few-layer graphene according to the present invention (excitation wavelength of 244 nm). The lonsdaleite peak is centred at around 1323.4 cm.sup.1.

[0069] FIG. 7 shows a UV Raman spectrum of ultrathin diamond sheets elaborated from the conversion of few-layer graphene according to the present invention (excitation wavelength of 244 nm). The diamond peak is centred at around 1333.1 cm.sup.1.

[0070] FIG. 8 shows a UV Raman spectrum of a graphenediamond sheet stack structure elaborated from the conversion of few-layer graphene according to the present invention (excitation wavelength of 244 nm). The diamond peak is centred at around 1330.1 cm.sup.1.

DETAILED DESCRIPTION OF THE INVENTION

[0071] The compositions and methods provided herein are based, in part, on previous investigations of the use of hot-filament chemical vapour deposition (HFCVD) for the growth of nanocrystalline diamond thin films and the conformal coating of carbon nanotube bundles by diamond and silicon carbide nanocrystals at low substrate temperature by the present inventors, as described in U.S. Pat. No. 9,458,017, Piazza, 2015. The preferred embodiments of the present invention demonstrate a simple and efficient route to production of detectable ultrathin and crystalline sp.sup.3 bonded carbon sheets. In the more preferred embodiments, the sheets have a lonsdaleite or diamond crystal structure, or a combination of these two structures.

[0072] Preferred methods of the present invention use an HFCVD for production of such materials. Use of HFCVD may be particularly advantageous due to its simplicity and ease of implementationpreviously, it has been used in a number of processes for the production of microcrystalline and nanocrystalline diamond films [M. A. Prelas et al. (1998); J. E. Butler et al. (2008); J. Zimmer. Et al. (2006)], because of the efficiency of production of atomic hydrogen, which has been shown to play an important role for the conventional synthesis of metastable diamond at low pressure from a dilute mixture of a hydrocarbon in H.sub.2. [M. A. Prelas at al. (1998); M. Frenklach et al. (1991); J. Stiegler, et al. (1997); S. A. Redman et al. (1999)]. When an HFCVD process is used, atomic hydrogen, H, is produced heterogeneously by the thermal decomposition of H.sub.2 on the hot filament surface, which then rapidly diffuses into the bulk gas. H recombination reactions are sufficiently slow at the process pressures used in the present invention that much of the atomic H diffuses to the reactor walls. Atomic H is present at super-equilibrium concentrations throughout most of the reactor. HFCVD process advantageously reduces the presence on ions accelerated towards the substrate, in comparison to e.g. low pressure plasma techniques. Accordingly, damage to the graphene starting material and/or the crystalline sp.sup.3-bonded carbon sheets can be reduced or avoided, because production of high kinetic energy ions (which tend to etch the sheets instead of participating in a hydrogenation process) is inhibited.

[0073] FIG. 1 shows a schematic of a hot-filament chemical vapour deposition (HFCVD) system as used in one method according to the present invention. The apparatus 100 comprises a vacuum chamber 1 having an inlet 3 for feed gas (represented by arrow), an outlet 4 to a vacuum pump, two filaments 5 (typically tungsten or rhenium wires) positioned approximately 1 cm apart, and on either side of the substrate 7 (here a vertically-positioned TEM grid having FLG disposed thereon) held by substrate support 9. Whilst the grid is vertically arranged in this schematic, the few-layer graphene grids can alternatively be placed horizontally on the substrate support, or at an angle to the substrate supportin other words, the grid may be disposed at an angle between 0 and 90 to the substrate support.

[0074] The substrate support is disposed on substrate holder 11, which comprises a fluid cooling system (not visible), a thermocouple 13 disposed immediately adjacent the substrate 7 for detecting the temperature of the substrate to allow for monitoring and control of the temperature of the substrate (e.g. by operation of the cooling system within the substrate holder) during operation of the HFCVD system. The substrate holder 11 is vertically moveable in the vacuum chamber 1. This allows for the substrate to be moved closer to, or further from, the filaments 5 as appropriate for the process being performed.

[0075] The temperature of the substrate 7 is controlled to be 325 C. or less, such that the temperature of the FLG on the substrate is about 325 C. or less.

[0076] A feed gas (here, H.sub.2) is flowed into the vacuum chamber at a flow rate of between 1 and 250 sccm. At the same time, the vacuum pump is operated, to maintain pressure in the vacuum chamber at a pressure of 100 Torr or less. The gas flow may be regulated by e.g. a mass flow controller, in a manner well known to the skilled person. The pressure may be regulated by e.g. an automatic valve located below the substrate holder.

[0077] The step of flowing the feed gas over the substrate is performed for a time sufficient to at least partially convert the few-layer graphene disposed on the substrate into ultrathin and crystalline sp.sup.3-bonded carbon sheets. The FLG is converted by hydrogenation of the few-layer graphene, followed by subsequent transformation of few-layer graphene into few-layer crystalline sp.sup.3-bonded carbon. Such hydrogenation of few-layer graphene can be detected by Fourier Transform Infrared (FTIR) spectroscopy and microscopy.

[0078] The precise configuration (number of layers, crystal structure etc.) of the ultrathin crystalline sp.sup.3-bonded carbon sheets can be detected and/or analyzed by a number of methods. For example, such sheets may be analyzed using one or more techniques selected from: visible or ultraviolet (UV) Raman spectroscopy; transmission electron microscopy (TEM); electron diffraction (ED); or electron energy loss spectroscopy (EELS).

[0079] In particular, for determining the crystallinity of the produced material, Raman spectroscopy is a particularly useful technique, due to its simplicity. A crystalline structure will generally display clear, sharp and distinct peaks corresponding to the various vibrational modes of the material. Comparatively, a Raman spectrum of an amorphous carbon sheet (e.g. ta-C, or diamond-like carbon), will generally display 2 broad and overlapping bands (the D and G bands). An example of a typical Raman spectrum from ta-C (tetrahedral sp.sup.3 amorphous carbon) can be seen in FIG. 48 of J. Robertson, Diamond-like amorphous carbon, Materials Science and Engineering. R 37, 129-281 (2002). For comparison with Raman spectra discussed below in relation to materials produced according to the present invention, the relevant spectra is that taken at an excitation wavelength of 244 nm.

EXAMPLES

Example 1

[0080] As received commercial chemical vapour deposition (CVD) graphene film deposited on 3 mm ultrafine copper transmission electron microscopy (TEM) grids (2000 Mesh) were used as graphene materials (from Graphene Supermarket, SKU # SKU-TEM-CU-2000-025). Graphene was grown by CVD from CH.sub.4 at 1000 C. on Ni substrate and transferred to a commercial TEM grid using polymer-free transfer methods to minimize contamination as described in W. Regan et al. (2010). The thickness of CVD graphene film was between 0.3-2 nm (1-6 monolayers). Typical graphene coverage of the TEM grid is between 60 and 90%.

[0081] A commercial HFCVD system from Blue Wave Semiconductors (BWI 1000 model) was used for hydrogenation and subsequent structure conversion of few-layer graphene into ultrathin and crystalline sp.sup.3-bonded carbon sheets. A schematic of this system is shown in FIG. 1, and described above.

[0082] The reactor is a six-way cross stainless steel vacuum chamber. It is fluid cooled (15% water, 75% glycol at 18 C.) with brazed copper tubing covered with an aluminium foil. The reactor is equipped with a molybdenum filament cartridge that accommodates between one and three 0.5 mm diameter straight metallic wires. Typically tungsten or rhenium wires are used. In this example, tungsten was used. Typically two 5.7 cm length wires, 1 cm apart, are used. Substrates were placed on the movable and fluid-cooled 5 cm diameter sample stage. The few-layer graphene grids were placed vertically on the substrate holder and were pinched by two (100) silicon pieces (500-550 m thickness, 14 mm14 mm) to keep their position fixed during operation.

[0083] The substrate temperature and the temperature of the few-layer graphene were estimated by a thermocouple tip located on top of the surface of the substrate holder located in front of the filaments. Before synthesis, the HFCVD system was evacuated to below 410.sup.4 mbar using a turbomolecular pump backed with a hydrocarbon oil pump.

[0084] For hydrogenation, ultra-high purity (UHP) H.sub.2 gas (about 99.999% pure) was the only gas introduced into the chamber via a stainless steel tube located on top of the chamber. Gas flow was regulated by an Omega mass flow controller. The pressure, P, was regulated via an automatic valve located below the substrate holder. The filament temperature, TF, was monitored with a two colour pyrometer (M90R2 model from Mikron Infrared, Inc.). The pressure and flow were 50 Torr and 1 sccm, respectively. Before synthesis, the tungsten filament was not exposed to activated hydrocarbon gas for carburization or conditioning as it is necessary for the conventional growth of diamond by HFCVD to stabilize filament temperature. This was to avoid carbon contamination from a carburized filament. The distance between the substrate holder and the filaments, d, was 22.8 mm. The current for both filaments, was kept constant, at 55 , which resulted in a filament temperature of 2330 C. The resulting substrate holder temperature was about 300 C. The maximum few-layer graphene temperature was of about 325 C., due to the closer proximity of the TEM grid substrate to the filaments. The duration of the hydrogenation process was 6 minutes and 20 seconds.

[0085] Material Analysis & Methods

[0086] Multi-wavelength Raman spectroscopy (RS) was employed to examine the material structure before and after hydrogenation. Raman spectra were recorded with a Renishaw InVia Reflex Spectrometer System with a stigmatic single pass spectrograph using the 244, 488 and 514.5 nm lines of Ar ion lasers. In the visible, 50 and 100 objectives were used. In the UV, 40 objective was employed. The laser power on the sample and acquisition time were adjusted to obtain optimum signal without any sample modification. No visible damage and no change of the spectral shape during measurements have been observed. Silicon and highly-oriented pyrolytic graphite (HOPG) were used for peak position calibration: silicon for spectra excited with visible radiation, and HOPG for spectra excited with deep UV radiation. Raman mapping was employed using high speed encoded mapping stage and a 1 CCD to generate high definition 2D chemical images over hundreds of microns square. CH bonds were directly detected using Fourier Transform Infrared (FTIR) spectroscopy. FTIR images and spectra were recorded with an Agilent Technologies Cary 670 FTIR spectrometer coupled to a Cary 620 FTIR microscope equipped with a 6464 focal plane array (FPA) mercury cadmium telluride (MCT) detector. Attenuated Total Reflection (ATR) mode, with a Germanium crystal as internal reflection element, was employed.

[0087] FIG. 2 shows FTIR-ATR image processed on the integrated intensity of CH stretching band. The image was obtained on the TEM grid material which is around the TEM grid mesh, and which was exposed to H.sub.2 gas activated by HFCVD. Prior treatment, this region of the grid contains few-layer graphene as evidenced by Raman spectroscopy analysis. FIG. 2 reveals a large-sized area of several microns square (up to about 10 m in diameter) containing CH bonding, which indicates that hydrogenation took place in the basal plane of graphene, not only in the edges of graphene domains.

[0088] FIG. 3 displays two absorbance spectra (vertically offset from each other for clarity) taken in the region identified by a white arrow in FIG. 2. FIG. 3 shows that the CH stretching band, which is centred at around 2844 cm.sup.1, is composed of only one of the 9 possible vibration mode components. The inventors believe that this mode corresponds to the C(sp.sup.3)-H stretching mode. This hypothesis is based on the following arguments: [0089] 1. Taking into account vibration modes in free molecules, within the wavenumber range of 2800 to 2900 cm.sup.1, it is expected to detect the following vibration modes: C(sp.sup.3)-H centred at around 2900 cm.sup.1, C(sp.sup.3)-H.sub.2 symmetrical centred at around 2875 cm.sup.1 and C(sp.sup.3)-H.sub.3 symmetrical centred at around 2850 cm.sup.1. However, although the infrared absorption cross-section of the CH stretching vibration modes is unknown in hydrogenated few-layer graphene and in ultrathin and crystalline sp.sup.3-bonded carbon sheets, it is expected that the C(sp.sup.3)-H.sub.2 symmetrical and C(sp.sup.3)-H.sub.3 symmetrical modes would be simultaneously detected with their antisymmetrical counterpart, which is not the case since the observed CH stretching band is composed of only one vibration mode component. Therefore, the (sp.sub.3)-H.sub.2 symmetrical and C(sp.sup.3)-H.sub.3 symmetrical modes are excluded. [0090] 2. The C(sp.sup.2)-H olefinic and C(sp.sup.2)-H aromatic modes are not considered as they are typically detected at much higher wavenumber, above 2975 cm.sup.1, considering the case of free molecules. [0091] 3. The C.sub.2H.sub.2 olefinic symmetrical and antisymmetrical modes are also typically detected at significantly higher wavenumber, above 2950 cm.sup.1, considering the case of free molecules. Furthermore, they would be accompanied by their anti/symmetrical counterpart, which is not the case here, since the observed CH stretching band is composed of only one vibration mode component.

[0092] The shift, by around 56 cm.sup.1, of the position of the C(sp.sup.3)-H mode peak, as compared to the corresponding position in free molecules, is theorised to result from the stress generated by the hydrogenation of few-layer graphene, the subsequent conversion of sp.sup.2 hybridization into sp.sup.3 hybridization and interlayer sp.sup.3-C bond formation.

[0093] The narrow, one component CH stretching band reveals that carbon atoms are bonded to one hydrogen atom. This one component narrow CH stretching band has never before been reported for hydrogenated graphene. Known disclosures on FTIR spectroscopy analysis of hydrogenated graphene report on a multi-component CH stretching band including C(sp.sup.3)-H.sub.3 modes instead of C(sp.sup.3)-H mode, consistent with graphene domains of reduced size which are hydrogenated only on their edges. Comparatively, the one component narrow CH stretching band shown here is representative of large-sized hydrogenated graphene planes.

[0094] FIG. 2 and FIG. 3 together therefore confirm the hydrogenation of few-layer graphene by the direct detection of CH bonding.

[0095] FIG. 4 shows exemplary UV Raman spectrum of lonsdaleite sheets elaborated from the hydrogenation of few-layer graphene and subsequent interlayer sp.sup.3-C bond formation, at low few-layer graphene temperature, according to the present invention. The spectrum is obtained in the vicinity of the region analysed by FTIR microscopy (FIGS. 2 and 3) and also in the TEM grid mesh where free-standing graphene is originally located.

[0096] The spectrum shown in FIG. 4 is different from the spectrum obtained before the hydrogenation process, which is composed of the G peak at around 1582 cm.sup.1 due to CC sp.sup.2 vibration. The spectrum shown in FIG. 4 displays two sharp peaks, centred at around 1063.0 cm.sup.1 and at around 1323.1 cm.sup.1, respectively. The full width at half maximum of those two peaks is of around 15.6 cm.sup.1 and 30.2 cm.sup.1, respectively. The peak centred at around 1063.0 cm.sup.1 is the T peak, due to CC sp.sup.3 vibration, found in amorphous carbon films as a low-intensity and broad band (A. C. Ferrari, J. Robertson, Resonant Raman spectroscopy of disordered, amorphous, and diamond-like carbon, Physical Review B 64, 075414(2001). Here, the T-peak is narrow and high-intensity, showing that the structure of the sp.sup.3-C in the material is crystalline. The peak centred at around 1323.1 cm.sup.1 is the lonsdaleite peak (E vibrational mode) [D. C. Smith et al. 2009); Y. G. Gogotsi, et al. (1998); L. A. Chernozatonskii et al. (2012)].

[0097] In amorphous carbon, the FWHM of the T peak is wide because of the amorphous structure of the material. In lonsdaleite, the FWHM is much lower because of the crystal structure of the material. The FWHM value of the lonsdaleite peak reveals confinement effects in few atomic layers. The detection of CC sp.sup.3 vibration and lonsdaleite in Raman spectra is consistent with the detection of only one component in the FTIR CH stretching band (FIGS. 2 and 3). The results show that lonsdaleite is elaborated from the free-standing few-layer graphene or from the few-layer graphene on the copper substrate.

[0098] In some regions of the grid, on the mesh and on the grid material, the peaks observed in FIG. 4 and ascribed to CC sp.sup.3 vibration and to lonsdaleite are simultaneously detected with the graphene peak at around 1582 cm.sup.1, as shown in FIGS. 5 and 6. This shows that it is possible to elaborate graphene-lonsdaleite stack structures. In the spectrum shown in FIG. 5, the T peak at 1061.6 cm.sup.1 (FWHM of 17.3 cm.sup.1), the lonsdaleite peak at 1323.5 cm.sup.1 (FWHM of 30.9 cm.sup.1) and the G peak at 1582.5 cm.sup.1 (FWHM of 26 cm.sup.1) are detected. In FIG. 5 the height of the T and lonsdaleite peaks is at least twice the height of the G peak. In the spectrum shown in FIG. 6, the T peak at 1062.4 cm.sup.1 (FWHM of 26.5 cm.sup.1), the lonsdaleite peak at 1323.4 cm.sup.1 (FWHM of 34.6 cm.sup.1) and the G peak at 1580.8 cm.sup.1 (FWHM of 22.2 cm.sup.1) are detected. In FIG. 6 the height of the G peak is several time higher than the height of the T and onsdaleite peaks. The inventors hypothesise that the variation of the relative intensity of the peaks related to sp.sup.2C and sp.sup.3C may be indicative of the ratio of sp.sup.2C and sp.sup.3C in the stack sequence.

[0099] FIG. 7 shows exemplary UV Raman spectrum of diamond sheets elaborated from the hydrogenation of few-layer graphene and subsequent interlayer sp.sup.3-C bond formation, at low few-layer graphene temperature, according to the present invention. The spectrum is obtained on the surface of TEM grid material which is around the TEM grid mesh and also in the TEM grid mesh where free-standing few-layer graphene are originally located. The spectrum shown in FIG. 7 is different from the spectrum obtained before the hydrogenation process, which is composed of the G peak at around 1582 cm.sup.1 due to CC sp.sup.2 vibration. The spectrum shown in FIG. 7 displays two sharp peaks: the T peak centred at around 1068.0 cm.sup.1 and at the diamond peak centred at around 1331.3 cm.sup.1, respectively. The full width at half maximum of those two peaks is of around 14.4 cm.sup.1 and 32.7 cm.sup.1, respectively. The FWHM value of the diamond peak reveals confinement effects in few atomic layers.

[0100] In some regions of the grid, on the mesh and on the material grid, the T and diamond peaks as shown in the FIG. 7 spectrum are simultaneously detected with the graphene peak at around 1582 cm.sup.1 (FIG. 8). This shows that it is possible to elaborate graphene-diamond stack structures. In the spectrum shown in FIG. 8, the T peak at 1066.5 cm.sup.1 (FWHM of 11.8 cm.sup.1), the diamond peak at 1330.1 cm.sup.1 (FWHM of 36.3 cm.sup.1) and the G peak at 1581.9 cm.sup.1 (FWHM of 25.5 cm.sup.1) are detected. In FIG. 8 the height of the diamond and G peaks is similar.

CONCLUSIONS

[0101] To summarize, a new process has been developed to obtain ultrathin and crystalline sp.sup.3-bonded carbon sheets, including ultrathin diamond sheets and including ultrathin lonsdaleite sheets, which are new nanomaterials, from the hydrogenation and subsequent interlayer sp.sup.3-C bond formation of few-layer graphene at low graphene and substrate temperature, below 325 C. and down to about 170 C., and at low pressure, below 100 Torr and down to about 5 Torr.

[0102] The synthesis of ultrathin and crystalline sp.sup.3-bonded carbon sheets, including ultrathin diamond sheets and including ultrathin lonsdaleite sheets, has been successfully demonstrated for the first time, via the exposure of few-layer graphene, to pure H.sub.2 activated by HFCVD. The inventors theorise that, depending on relative orientation of the graphene layers and when it is energetically favourable, the chemisorption of elements such as hydrogen on the graphene planes leads to the interlayer sp.sup.3-C bond formation required for formation of the ultrathin and crystalline sp.sup.3-bonded carbon sheet structure, in line with previous theoretical works in this field.

[0103] Large area of the planes of the few-layer graphene, exposed to hydrogen, are hydrogenated and carbon atoms are bonded to one hydrogen atom. The number of the sheets is typically between 2 and 6, but may be up to e.g. 10.

[0104] The temperature of the few-layer graphene and substrate during the process is about 325 C. This method is suitable for mass-production of ultrathin and crystalline sp.sup.3-bonded carbon sheets, including ultrathin diamond sheets and including ultrathin lonsdaleite sheets. The new process can also be used to obtain heterostructures of graphene and ultrathin and crystalline sp.sup.3-bonded carbon sheets.

[0105] Potential applications of these ultrathin and crystalline sp.sup.3-bonded carbon sheets elaborated from this method include but are not restricted to passive or active components in transistors and integrated circuits, components of thermal management devices, electrical field shields, components of field emission devices, components of quantum computing devices, building materials for micro-electro-mechanical systems, building materials for nano-electro-mechanical systems, components of ultrathin protective coatings, components of wear-resistant coatings, components of composite materials, components of tunnel devices, components of optical linear waveguides, components of lithium batteries, components of supercapacitors, components of biodevices, components of sensors, components of biosensors, components of an active laser medium, and components of optoelectronic sensors.

[0106] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0107] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0108] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0109] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0110] Throughout this specification, including the claims which follow, unless the context requires otherwise, the word comprise and include, and variations such as comprises, comprising, and including will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0111] It must be noted that, as used in the specification and the appended claims, the singular forms a, an, and the include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent about, it will be understood that the particular value forms another embodiment. The term about in relation to a numerical value is optional and means for example +/10%.

REFERENCES

[0112] A number of publications are cited above in order to more fully describe and disclose the invention and the state of the art to which the invention pertains. Full citations for these references are provided below.

[0113] The entirety of each of these references is incorporated herein. [0114] L. A. Chernozatonskii, P. B. Sorokin, A. G. Kvashnin, and D. G. Kvashnin, JETP Letters (2009) vol. 90, #2 pp. 134-138; Diamond-Like C.sub.2H Nanolayer, Diamane: Simulation of the Structure and Properties. [0115] D. C. Elias, R. R. Nair, T. M. G. Mohiuddin, S. V. Morozov, P. Blake, M. P. Halsall, A. C. Ferrari, D. W. Boukhvalov, M. I. Katsnelson, A. K. Geim, K. S. Novoselov, Science 323, 610-613 (2009); Control of Graphene's Properties by Reversible Hydrogenation: Evidence of Graphane. [0116] O. Leenaerts, B. Partoens, and F. M. Peeters, Physical Review B 80, 245422-1-245422-6 (2009); Hydrogenation of bilayer graphene and the formation of bilayer graphane from first principles. [0117] Liyan Zhu, Hong Hu, Qian Chen, Shudong Wang, Jinlan Wang and Feng Ding, Nanotechnology 22, 185202 (7pp) (2011); Formation and electronic properties of hydrogenated few layer graphene. [0118] Dorj Odkhuu, Dongbin Shin, Rodney S. 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