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

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.