G. L. Sharma

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 Eg (∼418 cm−1) and A1g(∼767 cm−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.

Hydrogen Sensing Properties of Copper-Doped Zinc Oxide Thin Films

A highly sensitive hydrogen gas sensor has been developed utilizing 3% copper-doped zinc oxide thin films. These films were deposited using pulsed laser deposition technique on quartz substrates with predeposited interdigitated platinum electrodes. The deposited films were characterized by X-ray diffraction and atomic force microscopy. The hydrogen sensing properties of the sensor were studied at three operating temperatures, viz., 50 °C, 100 °C, and 150 °C. We observed that the sensor shows good performance even at a low operating temperature of 50 °C for a very small concentration of hydrogen (10 ppm).

Structural properties of multiferroic CuFeO2 thin films prepared by RF sputtering

CuFeO2 thin films were grown on single crystalline sapphire substrates with c-axis orientation by rf sputtering method. The reitveld refinement analysis of X - ray diffraction data indicates the formation of delafossite structure and tended to be oriented along (001). Raman-scattering study of these thin films reveals that the films were oriented along (001) with rhombohedral R3¿m symmetry. Temperature dependent Raman spectra of CuFeO2 thin films were measured from 80K to1273K and we observed two optical modes at Eg (296cm¿1) and Ag (638cm¿1) showing anomalous frequency shifts with temperature, which were interpreted as an experimental evidence of combined effect of lattice expansion and anharmonic phonon - phonon interaction in CuFeO2.