THERMAL-DECOMPOSITION OF NICKEL CARBIDE - AUGER LINESHAPE STUDY

A carbon Auger spectrum indicative of nickel carbide is detected in thin films of nickel evaporated onto graphite in ultrahigh vacuum. Isothermal heating of the films leads to an irreversible change in the carbon Auger lineshape. This change is interpreted as evidence for the decomposition of the nickel carbide. Initial and final spectra are representative of carbide and graphite, respectively. It is seen that intermediate phases in the Auger lineshape transition are closely approximated by linear combinations of carbide and graphite spectra. This approximation allows the retrieval of the relative amount of nickel carbide present in the film as a function of time during a heating period. Rate constants are calculated for a number of temperatures. An energy of activation for the decomposition process is then obtained. The results of this experiment are in good agreement with previous measurements employing bulk techniques.