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 h ave been derived. The values of 3.30 and 2.30 N/cm for the shear motio ns perpendicular to the c axis have been obtained. Polarized Raman spe ctra of a thermally annealed WSi2 film reveal a preferred orientation of the layer; this effect is confirmed by X-ray diffraction. The therm al 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 wa venumbers, half-widths and intensities are strongly temperature depend ent. The frequency shift has been related to the thermal expansion of the crystal, using the Gruneisen theory. The important broadening of t he A(1g) mode with temperature is explained in terms of anharmonicity and the loss of intensity of the two lines is discussed.