A Kinetic Phase Diagram for Ultrathin Film Ni/Si(111): Auger Lineshape Results

Abstract

ABSTRACTWe have used Auger spectroscopy to monitor chemical reactions during solid phase epitaxy by contact reaction in the Ni/Si(ll1) ultrathin film system. We show that coexisting phases may be separated by numerically fitting the composite Si LVV lineshape using a linear combination of single phase “fingerprint” spectra. Sytematic measurements of coverage and temperature conditions are compiled into a kinetic phase diagram. Comparison with conventional (1000Å) thin film data suggest that the reactions forming Ni2Si and NiSi at > 20 Å thickness are bulk diffusion limited, while surface diffusion dominates at lower coverage. On the other hand, the formation of NiSi2 appears to be nucleation limited at all coverages, with dramatic variations in reaction rate with film thickness. This is discussed in terms of a competition between surface and bulk free energies.