Date of Graduation

Fall 2010

Degree

Master of Science in Materials Science

Department

Physics, Astronomy and Materials Science

Committee Chair

Saibal Mitra

Keywords

SnO2, MoO3, metal oxides, pulsed laser deposition, chemiresistor gas sensors

Subject Categories

Materials Science and Engineering

Abstract

Transitional metal oxides have widespread applications as gas sensors, battery electrodes and so on. In this project, we studied thin films of SnO2 and MoOx deposited on glass substrates with thickness ranging from 140 nm to 200nm using pulsed laser ablation of pure SnO2 and MoO3 targets in oxygen atmospheres. SnO2 films were deposited in oxygen atmospheres of 2 x 10-2 and 4 x 10-3 mbar pressures with the substrate at temperatures of 200oC, 300oC and 400oC, while the MoO3 films were deposited in oxygen atmosphere of 4 x 10-3 mbar pressure with the substrate at temperatures of 200oC, 300oC and 400oC. A KrF laser operating at 248 nm with pulse duration of 10 ns and repetition rate of 10 Hz was used to ablate the target. The on-target laser intensity was maintained ~ 7 J/cm2. The as-deposited SnO2 films were annealed in air at 500oC for four hours, whereas the MoO3 films were annealed in air at 450oC for an hour. Both the as deposited and annealed films were characterized using XRD, SEM, EDX and AFM. While all the SnO2 films consist of pure polycrystalline SnO2 phase, MoO3 films are polycrystalline with different MoOx phases. SEM studies have shown that the SnO2 films consist of tin oxide grains of 1 to 2 micrometers on the smooth tin oxide surfaces while the grain size of MoO3 films varied from sub-micrometer to a few micrometers and changed shape and size after annealing. Optical properties of these tin oxide films have been studied using a home-built UV-visible spectrometer with reference to a bare glass substrate. Initial results indicate the existence of intermediate states within the band gap of SnO2 films deposited at 2 x 10-2 mbar. Gas-sensing devices with gold electrodes, metal oxide thin films had been fabricated and studied using Keithley 2400 source meter.

Copyright

© Nagaraju Chada

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