Thermal and ion induced interfacial reactions between metal and graphite at elevated temperatures

Thermal and ion bombardment induced reactions at the interface between the chromium layer and graphite substrate have been studied, by means of Rutherford backscattering spectroscopy (RBS), auger electron spectroscopy (AES), and reflection of high energy electron diffraction (RHEED) techniques, under an ultra high vacuum (UHV) condition at temperatures between 400 and 7500C. It is found that thermal annealing at temperatures above 6500C for -- 15 hr forms the polycrystalline chromium carbide layer of a single Cr7C3 phase on graphite. On ion bombardment of category I, where the linear range of ions is smaller than the thickness of the chromium carbide layer, it is found that the chromium carbide layer is transformed into an amorphous phase but the carbon concentration in the chromium carbide layer is unchanged. On the other hand, on ion bombardment of category II, where the peak of range distribution is located at the interface, it is found that the Cr7C3 phase is transformed into a Cr3C2 phase, and moreover the normalized sputtering yields of Cr are more reduced than those in the category I, for the same removal rate of carbon atoms at the surface. The experimental results are discussed in terms of grain boundary diffusion, ion induced segregation, atomic mixing, and metastable carbide formation