Raman scattering measurements of phonon anharmonicity in CuAlO2 thin films

CuAlO2 thin films were grown on single crystalline sapphire substrates with c-axis orientation by rf sputtering method. The x-ray diffraction data indicate the formation of delafossite structure and tend to be oriented along (001). Temperature dependent Raman spectra of CuAlO2 thin films were measured from 80 to 1273 K, and we observed two optical modes at E-g (similar to 418 cm(-1)) and A(1g) (similar to 767cm(-1)) showing anomalous frequency and linewidth shifts with temperature, which were interpreted as an experimental evidence of combined effect of lattice expansion and anharmonic phonon-phonon interaction in CuAlO2. At high temperature, polaronic state and change in effective mass due to lattice expansion also affect the frequency shift and the linewidth of the observed Raman modes. (c) 2008 American Institute of Physics. [DOI: 10.1063/1.3031799]