Influence of mixing entropy on the nucleation of CoSi2

It is generally known that nucleation effects strongly influence the CoSi to CoSi2 phase transition. The small difference in Gibbs free energy between the CoSi and CoSi2 phase is responsible for the nucleation barrier. In this work, it is shown that the addition of elements that are soluble in CoSi and insoluble in CoSi2 or vice versa influences the entropy of mixing and thus changes DeltaG. In this way, the height of the nucleation barrier may be controlled, thus controlling the temperature of formation of the CoSi, phase in a thin film system. The influence of mixing entropy on silicide nucleation is illustrated by the effect of Fe, Ge, and Ni on CoSi2 formation. It is found that Fe has a higher solubility in CoSi than in CoSi2, causing an increase of the nucleation barrier. The presence of Ge increases the nucleation temperature, similar to what was observed for Fe, while the presence of Ni+ lowers the nucleation temperature. Based on the crystallographic structure of their respective monosilicides and disilicides, a list is given of other metals that are also expected to influence the nucleation temperature.