Sensors: High Selectivity Gas Sensing by Photostimulation of Semiconducting Metal Oxides

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The ability to sense an ever larger number of chemical species is essential for safeguarding the environment, protecting workers against toxic industrial chemicals, securing our nation against chemical weapons, insuring indoor air quality, improving productivity via closed loop process control and improving medical diagnosis. Semiconducting Metal Oxide Gas Sensors (MOGSs), while exhibiting high sensitivity to different vapor species and simple construction do, however, suffer from relatively limited selectivity inhibiting wider use. Furthermore, unlike polymers, MOGSs require heating to above 200C to insure sufficiently rapid kinetics thereby increasing complexity and power demands. In this research program, we explore a novel approach for activating sensitivity and tuning selectivity of MOGSs by using monochromatic light to promote charge-transfer interactions between the sensor and adsorbed gas molecules thereby eliminating the need for thermal excitation. Towards these ends we will examine the sensitivity and selectivity of illuminated n-type SrTiO3 thin films, prepared by PLD with controlled orientation and microstructure, to a number of reducing and oxidizing gases. DC and AC impedance and photo-current spectroscopy measurements will be performed, in situ, in a unique microprobe system for achieving an improved understanding of the sensing mechanisms. Small arrays of MOGSs with integrated LEDs will be assembled to demonstrate the ability to monitor a number of gases with high selectivity at room temperature. Similar devices will be prepared to serve as the basis of a laboratory experiment for undergraduate and high school students for demonstrating principles relating to semiconductor junctions under illumination, and their relevance to gas sensingSuccess along these lines would serve as a major breakthrough in the field of solid-state gas sensors and would create possibilities for the selective detection of numerous additional gases, improve device stability and lifetime as well as contribute to an improved fundamental understanding of the gas sensing phenomenon.