In situ x-ray diffraction study of graphitic carbon formed during heating and cooling of amorphous-C/Ni bilayers

Abstract

We examine graphitization of amorphous carbon (a-C) in a-C/Ni bilayer samples having the structure Si/SiO2/a-C(3–30 nm)/Ni(100 nm). In situ x-ray diffraction (XRD) measurements during heating in He at 3 °C/s to 1000 °C showed graphitic C formation beginning at temperatures T of 640–730 °C, suggesting graphitization by direct metal-induced crystallization, rather than by a dissolution/precipitation mechanism in which C is dissolved during heating and expelled from solution upon cooling. We also find that graphitic C, once formed, can be reversibly dissolved by heating to T>950 °C, and that nongraphitic C can be volatilized by annealing in H2-containing ambients.

Structural and physical properties of highly piezoresistive nickel containing hydrogenated carbon thin films

“…Saenger et al [23] also observed for a-C/Ni bi-layered thin films a graphitization of amorphous carbon at temperatures of 640-730°C, suggesting a metal-induced crystallization mechanism followed by a dissolutionprecipitation mechanism at higher temperatures. As observed in our experiments, both graphitization mechanisms are possible for temperatures slightly above 500°C for the Ni-C thin films described here.…”

Synthesis of large area, homogeneous, single layer graphene films by annealing amorphous carbon on Co and Ni

“…In the case of lower a-C thickness (1.0 nm), graphene can be grown even when the samples were cooled down immediately after reaching the annealing temperature (0 min staging time). This suggests that the graphene growth on our highly crystalline substrate may not all be via dissolution-precipitation but could also be by direct crystallization during heating as observed by Saenger et al [22]. For example, the Raman spectrum shown in Fig.…”

Introducing Carbon Diffusion Barriers for Uniform, High-Quality Graphene Growth from Solid Sources

“…We thus show that a key problem with solid-state graphene growth, relevant to all previous literature, is the lack of an “on-switch” for the carbon supply. Carbon is uncontrollably fed during temperature ramping into a catalyst film, 10 whose grain size distribution is still rapidly changing, leading to defective and inhomogeneous graphene nucleation at temperatures well below the maximum process temperature, that degrades the overall growth result. Carbon diffusion short-circuits through the evolving grain boundaries of the polycrystalline catalyst that can thereby further lower the graphene growth homogeneity.…”