Low temperature crystallization of diamond-like carbon films to graphene

Plasma surface modification was used to fabricate graphene on the top of insulating diamond-like carbon films. It is shown that by a combination of pulsed argon plasma treatment and thermal annealing at 350 ̊C it is possible to achieve crystallization of amorphous carbon to graphene. The observed Raman spectra are typical for defected graphene-splitted D- and G-peaks and a broad 2D-peak. Because interpretation of Raman spectra of such complicated system is not easy we have calculated Raman signals of graphene on an amorphous hydrogenated carbon film deposited on a Si substrate. Our simulation results show that multiple reflections and interference effects lead to enhancement of Raman signal of the system. The characteristic for graphene G and 2D bands reach maximal enhancement for thicknesses of the amorphous hydrogenated carbon film of about 75 nm and 230 nm. We estimate that the interference enhancement of the 2D graphene Raman signal is very weak in contrast to that of the G band signal simulated for the underlying diamond-like carbon films on silicon substrate only. Therefore experimentally measured Raman spectra of the whole graphene/a-C:H/Si system probably will consist of interference enhanced but still weak 2D graphene peak and stronger D and G peaks dominated by G and D Raman bands of the a-C:H. This conclusion is in line with observed experimental Raman spectra. Electrical field effect measurements of the samples show ambipolar dependence, typical for single-layer graphene.