Browsing by Author "Lin, Yi-Chieh"

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A mechanistic study of hydrogen gas sensing by PdO nanoflake thin films at temperatures below 250 degrees C
(2015-01-01)
Chiang, Yu-Ju
;
Li, Kuang-Chung
;
Lin, Yi-Chieh
;
Pan, Fu-Ming
;
材料科學與工程學系
We prepared PdO nanoflake thin films on the SiO2 substrate by reactive sputter deposition, and studied their sensing response to H-2 at temperatures between 25 and 250 degrees C. In addition to the oxygen ionosorption model, which is used to describe the early H-2 sensing response over the temperature range studied, the H-2 sensing kinetics of the PdO thin films can be separated into three temperature regimes: temperatures below 100 degrees C, around 150 degrees C and above 200 degrees C. At temperatures below 100 degrees C, PdO reduction is the dominant reaction affecting the H-2 sensing behavior. At temperatures around 150 degrees C, Pd reoxidation kinetically competes with PdO reduction leading to a complicated sensing characteristic. Active PdO reduction by H-2 promotes the continuing growth of Pd nanoislands, facilitating dissociative oxygen adsorption and thus the subsequent Pd reoxidation in the H-2-dry air gas mixture. The kinetic competition between the PdO reduction and reoxidation at 150 degrees C leads to the observation of an inverse of the increase in the sensor conductivity. At temperatures above 200 degrees C, the PdO sensor exhibits a sensor signal monotonically increasing with the H-2 concentration, and the H-2 sensing behavior is consistent with the Mars-van-Krevelen redox mechanism.
Effects of PdO decoration on the sensing behavior of SnO2 toward carbon monoxide
(2016-04-01)
Lee, Kuang-Chung
;
Chiang, Yu-Ju
;
Lin, Yi-Chieh
;
Pan, Fu-Ming
;
材料科學與工程學系
We deposited PdO nanoparticles on SnO2 thin films and studied the CO gas sensing behavior of the PdO-decorated sensors at temperatures below 250 degrees C. The PdO nanoparticles and the SnO2 thin film were both prepared by reactive sputter deposition. The PdO decoration increases the resistivity of the SnO2 thin film as a result of the formation of the P -N junction. The sensing behavior of the sensor at 100 degrees C and below can be understood simply by the oxygen ionosorption model. At temperatures at 150 degrees C and above, the sensor demonstrates a fast response followed by a progressive conductance decay during the CO exposure. The observation is likely related with adsorption kinetics of CO and O-2 on Pd nanoislands formed as a result of PdO reduction. PdO reduction and reoxidation occur in the temperature range between 100 and 150 degrees C under the CO sensing condition, and thereby greatly influencing the sensing behavior of the sensor. The sensor signal of the PdO-decorated sensor is about three times that of the bare SnO2 sensor at 150 degrees C and above. The PdO decoration also significantly reduces the recovery time of the SnO2 sensor. The faster recovery is ascribed to the presence of the residual metal Pd phase, which promotes the spill -over effect. (C) 2015 Elsevier B.V. All rights reserved.