Thermal expansion of the isostructural PtSi and NiSi: Negative expansion coefficient in NiSi and stress effects in thin films

NiSi displays the rare occurrence of contracting during heating along the axis with the smallest unit cell dimension. Because of stress due to the thermal mismatch between the film and the Si substrate, the unit cell dimensions reported in the Joint Committee on Powder Diffraction Standards record for NiSi are faulty. They seem to be reproducible in thin films prepared by reactive diffusion, but do not correspond to relaxed equilibrium conditions. For PtSi (isostructural with NiSi), there is neither expansion nor contraction along the axis with the small dimension during heating. In the present PtSi film, x-ray diffraction does not reveal any presence of residual thermal stresses at low temperature. (C) 2003 American Institute of Physics.