Browsing by Author "Chiang, Yu-Ju"

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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.
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
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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.
Metal-Cu2O core-shell nanocrystals for gas sensing applications: Effect of metal composition
(2014-12-01)
Lin, Yin-Kai
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Chiang, Yu-Ju
;
Hsu, Yung-Jung
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材料科學與工程學系
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Department of Materials Science and Engineering
A fast, versatile citrate-binding approach has been developed to prepare metal-Cu2O core-shell nanocrystals with different metal compositions, such as Au, Ag and Pd. Because of the electron trapping of the metal core, metal-Cu2O nanocrystals exhibited enhanced CO sensing performance in comparison with pure Cu2O. Steady-state photoluminescence and photocurrent measurements were conducted to investigate the electron trapping effect of the metal and its significance in the CO sensing mechanism. Among the three metal-Cu2O nanocrystals tested, Au-Cu2O displayed the highest CO response, attributable to the largest electron trapping capability of Au which enlarged the extent of resistance change for CO detection. The ability to improve the gas sensing performance of Cu2O by means of metal introduction has significant implications in the development of gas sensor technology, especially the strategies of materials combination and heterostructure engineering. (C) 2014 Elsevier B.V. All rights reserved.
NEXAFS spectra and specific dissociation of oligo-peptide model molecules
(2019-08-01)
Chiang, Yu-Ju
;
Huang, Wan-Chou
;
Ni, Chi-Kung
;
Liu, Chen-Lin
;
Tsai, Cheng-Cheng
Total-ion-yield near-edge X-ray absorption fine-structure (NEXAFS) spectra of three oligo-peptide model molecules were recorded. The NEXAFS spectra were also calculated with time-dependent density functional theory; the calculated spectra are consistent with the experimental measurements. The ionic products from core-excited molecules and their branching ratios as functions of excitation energy show branching ratios 42%-75% of dissociation of the peptide bond, especially at resonant excitations. The major destination orbitals assigned at these excitation energies show significant antibonding character along peptide bonds, which causes large probabilities of bond cleavage. (C) 2019 Author(s).
PdO Nanoflake Thin Films for CO Gas Sensing at Low Temperatures
(2013-08-01)
Chiang, Yu-Ju
;
Pan, Fu-Ming
;
材料科學與工程學系
;
Department of Materials Science and Engineering
We prepared PdO nanoflake thin films by reactive sputter deposition and studied their gas-sensing response to CO at temperatures below 250 degrees C. The PdO thin film, which has a large open surface area allowing for rapid and extensive CO adsorption, exhibits a complicated CO sensing behavior. At temperatures below 150 degrees C, the electrical conductance of the thin film drops upon the exposure of the CO/dry air gas mixture. The CO sensing mechanism in this temperature range is described by the oxygen ionosorption model. At 150 degrees C, oscillatory response occurs when the CO concentration is larger than 2000 ppm. The oscillatory response is due to the reactivity switching between the PdO reduction and reoxidation reactions. In addition, the PdO thin film shows a rapid increase in the conductance before and after the oscillatory response regime. The conductance increase is ascribed to the positive charge accumulation at the interface between the PdO thin film and metal Pd nanoislands, which are formed during the PdO reduction. At temperatures higher than 150 degrees C, the conductance drops when the PdO thin film is exposed to CO. Besides the ionosorption model, the oxygen vacancy model is used to account for the CO sensing response of the thin film in the high-temperature range. On the basis of the inverse change in the CO sensing sensitivity at 150 degrees C, a CO sensor of high selectivity, which integrates two PdO sensing elements operating independently at 150 degrees C and a lower temperature, is proposed.
Specific dissociation of core-excited pyrimidine nucleobases
(2018-08-16)
Chiang, Yu-Ju
;
Lin, Yi-Shiue
;
Lin, Huei-Ru
;
Liu, Chen-Lin
;
應用化學系
Total-ion-yield near-edge X-ray absorption fine structure spectra of pyrimidine nucleobases were recorded. The phenomenon of specific dissociation, such as a larger branching ratio of some ionic fragments at resonant excitation energies, was observed. From the details of the specific dissociation channels, the larger branching yields at pi*-resonant excitations indicate that local bond cleavages around the atom excited is responsible for producing these ions; local excitation thus plays a major role in the site-specific dissociations. Using the NEXAFS spectra, representative ions and their branching ratios, we propose some improved ways to determine the quantities of pyrimidine nucleobases in DNA and RNA. (C) 2018 Elsevier B.V. All rights reserved.