XAFS study of Ni surroundings in metal induced crystallization of thin film amorphous silicon

EXAFS investigation about Metal Induced Crystallization (MIC) of a-Si thin films doped with Ni, has been carried out at the K edge of Ni. Several a-Si films deposited on quartz and annealed at different temperatures and a non-annealed sample have been analyzed in order to study the variation of the nickel surroundings as a function of temperature. Nickel particles were co-sputtered together with silicon to obtain a metal percentage of about at. 0.5%. In all the annealed samples it was found that nickel, in its first shell, is 8-fold coordinated to silicon while a weak signal corresponding to the second shell appears in the Fourier transform of the spectra as in crystalline nickel di-silicide (c- NiSi2) used as reference compound. No presence of Ni clustering has been ascertained. In the non-annealed sample, where the NiSi2 formation has never been observed, EXAFS shows a deformed first shell environment on Ni similar to that of NiSi2.