Silicon-rich silicon oxide thin films have been prepared by thermal evaporation of silicon monoxide in vacuum. The SiOx film composition (1.1⩽ x ⩽1.7) has been controlled by varying the deposition rate and residual pressure in the chamber. Long time stability of all films has been ensured by a postdeposition annealing at 523 K for 30 min in Ar atmosphere. Some films were further annealed at 973 K and some others at 1303 K. Raman scattering measurements have implied the formation of amorphous silicon nanoparticles in films annealed at 973 K and Si nanocrystals in films annealed at 1303 K. The latter conclusion is strongly supported by high resolution electron microscopy studies which show a high density of Si nanocrystals in these films. Photoluminescence has been observed from both amorphous and crystalline nanoparticles and interpreted in terms of band-to-band recombination in the nanoparticles having average size greater than 2.5 nm and carrier recombination through defect states in smaller nanoparticles.

The high-pressure Raman spectra of ZnF 2 have been measured up to 6.8 GPa and provided unambiguous evidence of a phase transition from its ambient-pressure rutile ͑D 4h 14 ͒ to the CaCl 2 -type orthorhombic ͑D 2h 12 ͒ structure at a pressure P c Ϸ 4.5 GPa. Both macro-and micro-Raman spectra have been independently obtained at high pressures leading to the same conclusion about the high-pressure phase and the P c . The transition appears to be closely associated with the B 1g ͑A g ͒ Raman-active soft mode of the rutile ͑CaCl 2 ͒ structure, implying that ZnF 2 undergoes a second-order ferroelastic phase transition.

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