Sputtering of metal layers deposited on graphite at elevated temperatures

The sputtering yield and compositional change of chromium carbide layers (Cr7C3) on graphite as a result of bombardment with 5 keV Ar+ and 80 and 150 keV Ne+ ions have been studied as a function of ion flux, temperature and thickness. In category I where the linear range of the ions is smaller than the thickness of the chromium carbide layer, it is found that the sputtering yield of Cr normalized to the elemental sputtering yield is about 0.5 at low removal rates of carbon atoms and is about 0.7 at high removal rates. The carbon concentration in the chromium carbide layer is unchanged during irradiation. On the other hand, in category II, where the projected range distribution is located at the interface, it is found that the Cr7C3 phase is transformed into a Cr3C2 phase. Moreover, the normalized sputtering yield of Cr is reduced for the same removal rates as those in category I and decreases with increasing temperature. The experimental results are discussed in terms of ion-induced segregation, atomic mixing and metastable carbide formation. (orig.)