We investigated the photocbromic (PC) and electrocbromic (EC) behavior of sputtered tungsten oxide (W0 3 _ 1 ) films with different oxygen deficiency y. It was found that both the PC and EC coloration efficiency increase with increasing oxygen deficiency in tungsten oxide. For PC efficiency, this behavior is consistent with the model of photocbromism developed recently. A recently developed model based on the small polaron transition between w S+ and W'+ states has been used to explain the dependence of EC coloring efficiency on the oxygen deficiency in tungsten oxide films. This new mechanism also revealed a close relationship between PC and EC. C 1997 Published by Elsevier Science Ud. All rights reserved

The aim of this project was to engineer the materials studied to enhance the so-called 3S criteria: Sensitivity, Selectivity, and Stability, by using the advantage of controlling structure and properties at nanometer dimensions. It targeted sensor materials that are able to detect poisonous gases resulting from coal-gasification processes, especially sulfur containing emissions. Research findings based on this award demonstrate that doping tungsten oxide (WO 3) with a small amount of Ti (e.g. 5% in our work) results in a new material that has a higher structural symmetry (e.g. tetragonal morphology) as well as narrower crystalline particle size distribution. As high quality materials with excellent ordered structure and narrower particle-size distributions (which can also withstand high-temperature technological environments such as those encountered in furnaces and coal gasification systems without their structure being affected by phase transformations) are needed for developing new, more sensitive sensor materials, W-Ti-O thin films grown by RF sputtering are valuable candidates for such roles. It is well known that pure WO 3 will change its structure at elevated temperatures. Our work indicates that, Ti doping not only increases the stability of the resultant material by promoting structural phase modifications, but also increases its sensitivity by increasing the effective surface area exposed to the poisonous gas (fine microstructure and uniform distribution were observed). Study the characteristics of undoped WO 3 thin films synthesized by RF sputtering……………..5 Explore the stabilization and structural modifications of Ti-doped WO 3 thin films……………….6 Determine computationally the amount of Ti doping that will maximize material structural stability………………………………………………………………………………………………… 8 Investigate sensitivity and stability of WO 3 thin films under gas testing………………………….11 Promoting research and education in the area of sensors and controls………………………....12 CONCLUSIONS……………………………………………………………………………………...13 5 EXECUTIVE SUMMARY The overall efforts proposed were to develop high-quality new sensor materials for achieving improved response time, controlled microstructure for long-term stability, and narrow particle size distribution for improved sensor characteristics and performance. The aim was to identify methods to enhance the so-called 3S criteria: sensitivity, selectivity, and stability, by utilizing the advantages of controlling structure and properties at nanometer dimensions. The milestones of the proposed research were: (1) to study the characteristics of undoped WO 3 thin films synthesized by RF sputtering, (2) to explore the stabilization and structural modifications of Ti-doped WO 3 thin films, (3) to determine computationally the amount of Ti doping that will maximize material structural stability, (4) to investigate sensitivity and stability of WO 3 thin films under gas testing, and (5) to promote research and education in the area of sensors and controls. The effect of processing conditions on the ...

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