Tungsten oxide thin films for hydrogen sulfide sensor application in energy systems
The sulfur containing emissions in coal gasification systems to produce energy are devastating and hostile to the requirements of clean, environmental friendly, efficient, and economical energy. Therefore, hydrogen sulfide (H 2S) emissions in coal gasification plants must be monitored, controlled and effectively removed before the syngas is used for energy production. The present research focuses on the development and utilization of tungsten oxide (WO3) thin films and nanostructures for H2S application in the coal gasification systems. As a part of that overall goal, the present work was performed with a specific objective of understanding the effect of growth temperature on WO3 nanocrystalline films fabricated by reactive magnetron sputtering. WO3 films were grown under varying deposition temperatures in the range of 30 (RT)–500°C. The effect of growth temperature on the crystal structure, surface/interface morphology, chemical quality and electronic properties is investigated in detail. Characterizations on the WO3 materials were performed using a wide variety of analytical tools viz., X-ray diffraction (XRD), high resolution scanning electron microscopy (HRSEM), energy dispersive X-ray spectrometry (EDS), UV-VIS-NIR double-beam optical spectrophotometer, and electrical resistivity measurements. XRD and SEM analyses indicate that the WO3 films grown at RT were amorphous while those grown at higher temperatures are nanocrystalline. The grain size ranged from 12-62 nm as the temperature increased from 100 to 500°C. It was observed that the films exhibited a smooth morphology below 300°C and a rough morphology above 300°C. XRD results indicated that the films grown at 100-300°C were monoclinic while those grown at higher temperatures exhibited a tetragonal phase. Optical properties of the WO3 films indicate that, as the growth temperature is increased, the transmittance of the films decreases. The band gap determined from optical measurements showed quantum confinement effects due to reduction in crystallite size. The band gap decreased from 3.25 eV to 2.92 eV with increasing temperature from RT to 500°C. The electrical measurements indicate that with an increase in substrate temperature the resistivity of the films decreases. A direct correlation between microstructure and electronic properties is derived. The results and implications for technology are discussed along with a recommendation of future directions.
Condensed matter physics|Nanotechnology
Gullapalli, Satya Kiran, "Tungsten oxide thin films for hydrogen sulfide sensor application in energy systems" (2010). ETD Collection for University of Texas, El Paso. AAI1479557.