A Raman study of single crystal and thin film tetragonal WSi2

A polarized Raman study of tetragonal monocrystalline WSi2 is reported. The two Raman lines of WSi2 have been assigned in terms of symmetry. Using a linear chain model, force constants of 6.64 and 3.16N/cm for compressive Si-Si and Si-W motions along the c axis of the unit cell have been derived. The values of 3.30 and 2.30 N/cm for the shear motions perpendicular to the c axis have been obtained. Polarized Raman spectra of a thermally annealed WSi2 film reveal a preferred orientation of the layer; this effect is confirmed by X-ray diffraction. The thermal behavior of the WSi2 Raman lines has been analysed both for single crystal and thin film over a wide temperature range (79-853 K). The wavenumbers, half-widths and intensities are strongly temperature dependent. The frequency shift has been related to the thermal expansion of the crystal, using the Gruneisen theory. The important broadening of the A(1g) mode with temperature is explained in terms of anharmonicity and the loss of intensity of the two lines is discussed.