Optical properties of Na0.68CoO2 thin film

Abstract

The optical reflectance of single-crystalline Na0.68CoO2 (thickness around 3000 angstrom) thin film has been measured over a wide frequency (40-55000 cm(-1)) and at temperatures between 20 and 300 K. The room-temperature optical conductivity spectrum displays a metallic character. In addition, one E-1u phonon mode at about 518 cm(-1) is identified, while the other four phonon peaks are due to the sapphire substrate. As the temperature is lowered, the Drude plasma frequency exhibits little temperature dependence, whereas the scattering rate monotonically decreases with decreasing temperature. Notably, the Drude scattering rate at 20 K is found to approach zero, consistent with the small residual resistivity, indicating high quality of Na0.68CoO2 thin film. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.