Raman effect and structure of YH3 and YD3 thin epitaxial films - art. no. 134109

The first-order Raman spectra of YH3 and YD3 thin epitaxial films deposited on CaF2 substrates have been studied in the temperature range from 4 to 30 0 K. Several rather broad Raman lines from YH3 have been found. The linewid th becomes smaller with decreasing temperature and the lines are very disti nct and sharp at 4 K. No indications for phase transitions are found. Isoto pically exchanged samples give a clear indication that YH3 is at the origin of the Raman lines. Polarization resolved measurements together with a fac tor group analysis for all suggested crystal structures of YH3 reveals the number and the symmetry of the phonon modes. The number of observed A(1) mo des is not compatible with a P (3) over bar c1 structure. Calculations of t he angular dependence at different inclination angles result in predictions for characteristic intensity patterns for the suggested crystal structures . The measured angular intensity pattern show no indications for a P (3) ov er bar c1 structure. In measurements at different inclination angles new Ra man lines appear, which points towards a P6(3)cm or P6(3) structure. Also t he comparison of the energies of the lines in the Raman and in IR spectra p romotes the picture of a noncentrosymmetric structure such as P6(3)cm or P6 (3).