Browsing by Author "Lee, Kuang-Chung"

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Effects of PdO decoration on the sensing behavior of SnO2 toward carbon monoxide
(2016-04-01)
Lee, Kuang-Chung
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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.
Effects of Pt Decoration on the CO Sensing Reaction Mechanism of PdO Nanoflakes Thin Films
(2015-07-30)
Chiang, Yu-Ju
;
Lee, Kuang-Chung
;
Pan, Fu-Ming
;
材料科學與工程學系
;
Department of Materials Science and Engineering
We sputter-deposited Pt nanopartides on a PdO nanoflake thin film and studied the CO sensing behavior of the Pt-decorated PdO (Pt-PdO) sensor at temperatures below 250 degrees C. According to X-ray photoelectron spectroscopy and temperature-programmed desorption, Pt nanoparticles can modify the electronic structure of the PdO thin film, thus improving the kinetics of PdO reduction by CO. The CO sensing response of the Pt-PdO sensor is greatly influenced by PdO reduction and reoxidation in the temperature range between 100 and 200 degrees C. The dramatic difference in the CO sensing behavior at 150 degrees C between the Pt-PdO and the bare PdO sensors is ascribed to the kinetic competition between PdO reduction and oxidation of growing Pd nanoislands on which dissociative oxygen adsorption takes place. On the other hand, the CO sensing characteristic of the Pt-PdO sensor at 100 degrees C and below is similar to that of the bare PdO sensor because PdO reduction is negligible in the temperature range. The Pt-PdO sensor exhibits a distinct delay in the recovery profile at 100 degrees C as a result of the sluggish replacement of CO adspecies by oxygen on Pt nanoparticles. At temperatures above 200 degrees C, the sensing behavior of the Pt-PdO sensor can be understood on the basis of the oxygen vacancy model. A highly CO-selective sensor based on the pattern recognition of the peculiar sensing response profile at 150 degrees C is suggested.