Conversion of multilayer graphene into continuous ultrathin sp3-bonded carbon films on metal surfaces

Abstract

The conversion of multilayer graphenes into sp 3 -bonded carbon films on metal surfaces (through hydrogenation or fluorination of the outer surface of the top graphene layer) is indicated through first-principles computations. The main driving force for this conversion is the hybridization between sp 3 orbitals and metal surface d z 2 orbitals. The induced electronic gap states and spin moments in the carbon layers are confined in a region within 0.5 nm of the metal surface. Whether the conversion occurs depend on the fraction of hydrogenated (fluorinated) C atoms at the outer surface and on the number of stacked graphene layers. In the analysis of the Eliashberg spectral functions for the sp 3 carbon films on a metal surface that is diamagnetic, the strong covalent metal-sp 3 carbon bonds induce soft phonon modes that predominantly contribute to large electron-phonon couplings, suggesting the possibility of phonon-mediated superconductivity. Our computational results suggest a route to experimental realization of large-area ultrathin sp 3 -bonded carbon films on metal surfaces. D iamond is known for its extraordinary thermal conductivity and mechanical hardness, and the production of large-area crystals has been a long term goal. The conventional synthetic methods employed for the production of artificial diamond usually require extremely high pressure and temperature 1,2 , or plasmaenhanced chemical vapor deposition (CVD) [3][4][5] . Advances in the growth of large-area graphene 6,7 and bilayer graphene through multilayer graphenes 8-10 suggest another possibility: the chemical conversion of a few layers of graphene into sp 3 -bonded carbon films. For example, previous theoretical results showed that the complete hydrogenation 11 or fluorination 12 of a single-layer of graphene can yield a thermodynamically stable sp 3 -bonded carbon layer. Indeed, partial hydrogenation of monolayer graphene 13,14 and evidence of complete fluorination of monolayer graphene membranes 15 have been experimentally achieved. Similarly, the conversion of a few layers of graphene has attracted attention, and hydrogenation of the outer surfaces of bilayer graphene 16,17 to achieve all sp 3 -bonded carbon films has been treated theoretically. We suggest however that such an approach will be challenging experimentally as extensive hydrogenation or fluorination was stated to be needed on both the top and bottom surfaces.Here we present a promising alternative, namely the conversion of graphene layers on a metal surface into sp 3 carbon films through surface hydrogenation or fluorination. From the practical point of view, the commonly used methods for growing graphene films on a metal substrate, either through CVD or as a result of the transfer of grown graphenes [6][7][8][9][10]18 , are already providing appropriate target systems for the study of the sp 2 to sp 3 conversion of carbon films on metal surfaces. Our computation results suggest a method of preparing an ultrathin 'diamond' layer over even very large area by conversion of appr...

First-principles investigation of wet-chemical routes for the hydrogenation of graphene

“…Such a thin sp 3 carbon material, strongly bonded to a metal surface, may serve as a protective layer with anticorrosion or diamond-like hardness. We have also shown that the interface between the metal surface and the sp 3 carbons can have particular electron-phonon structures which can possibly produce superconductivity [13].…”

“…Previously we have shown that the hydrogenation of the outer surface of stacked graphene on a metal surface results in an sp 3 -bonded carbon film which leads to strong covalent bond formation between the carbon sp 3 orbitals and metal surface 3d orbitals [13]. Such a thin sp 3 carbon material, strongly bonded to a metal surface, may serve as a protective layer with anticorrosion or diamond-like hardness.…”

“…This new material is expected to have important applications in hydrogen storage [5][6][7], nanoelectronics [8], cold cathode emitters [9], and as an ultrathin waveguide in optoelectronics [10,11]. Theoreticians and experimentalists have investigated methods for obtaining sp 3 -bonded atomic carbon films [12], and, with this motivation, the conversion of the graphene layers into sp 3 -bonded carbon films, through the fluorination and hydrogenation of the surface, is now the target of many focused studies [13][14][15][16][17][18][19].…”

Graphene fiber: a new trend in carbon fibers

“…In terms of mechanics, more regular alignment and more compact microstructure can be achieved by the optimization of the spinning process parameters, such as stretching ratio, spinning velocity and so on. In the atomic aspect, the enhancement of interlayer action between graphene sheets should increase the mechanical strength of GF, either by introducing external crosslinking reagents into the interlayer gallery or by partly transforming graphene sheets into diamond structures [98]. Importantly, the structural model of GF should be established from more detailed characterizations and the corresponding properties.…”

Electron paramagnetic resonance and Raman spectroscopy studies on carbon-doped MgB2 superconductor nanomaterials

“…This finding is corroborated based on theory by first principle studies. 53 The concentration of defect centers can also be determined by EPR. For this purpose, the first-derivative EPR signal is doubly integrated.…”