Effect of particle size and laser power on the Raman spectra of CuAlO2 delafossite nanoparticles

A transparent conductive oxide CuAlO2 delafossite is studied using x-ray powder diffraction (XRD) and micro-Raman spectroscopy measurements as a function of the particle size and laser power from 2 to 20mW. The XRD results indicate that the lattice parameters and the cell volume expand as the particle size reduces. Large red shifts (similar to 60 cm(-1)) and line broadening (similar to 50 cm(-1)) are observed as the particle size becomes of the order of 13 nm. These huge values can only be justified if collective effects on the Raman spectra created by the lattice expansion, confinement of phonons and enhanced phonon-phonon interactions are included in the interpretations of the Raman spectra of the CuAlO2 nanoparticles.