Ammonia gas detection by pure and catalytically modified WO 3 -based gas sensors was analyzed. Sensor response of pure tungsten oxide to NH 3 was unsatisfactory, probably due to the unselective oxidation of ammonia into NO . Copper and vanadium were introduced in different concentrations and the resulting material was annealed at different temperatures in order to improve the sensing properties for NH 3 detection. The introduction of Cu and V as catalytic additives improved the sensor response to NH 3 . Possible reaction mechanisms of NH 3 over these materials are discussed. Sensor responses to other gases like NO 2 or CO and interference of humidity on ammonia detection were also analyzed so as to choose the best sensing element.
Abstract-In this work, electrical measurements show that the breakdown voltage, BV DG , of InP HEMTs increases following exposure to H 2 . This BV DG shift is nonrecoverable. The increase in BV DG is found to be due to a decrease in the carrier concentration in the extrinsic portion of the device. We provide evidence that H 2 reacts with the exposed InAlAs surface in the extrinsic region next to the gate, changing the underlying carrier concentration. Hall measurements of capped and uncapped HEMT samples show that the decrease in sheet carrier concentration can be attributed to a modification of the exposed InAlAs surface. Consistent with this, XPS experiments on uncapped heterostructures give evidence of As loss from the InAlAs surface upon exposure to hydrogen.
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