Browsing by Author "Chin, TS"

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Effect of as-deposited residual stress on transition temperatures VO2 thin films
(2004-08-01)
Tsai, KY
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Chin, TS
;
Shieh, HPD
;
Ma, CH
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光電工程學系
Transmittance loops upon thermal cycling of VO2 thin films were found to change among films with different fabrication conditions that lead to different transition temperatures (Tts) from that of a strain-free VO2 single crystal, 68 degreesC. The residual stresses in the films quantitatively determined from x-ray diffractometry were used to explain this variation. Electron spectroscopy for chemical analysis spectra showed that the difference in the binding energy of core electrons 2p(1/2) and 2p(3/2) of the vanadium atom are affected by residual stress and proportional to Tts of the films. The bond length between vanadium and oxygen atoms at room temperature varies with different residual stresses and, furthermore, affects the movements of both atoms during phase change (and hence the Tt of VO2 thin films). Residual stresses also affect the hysteresis span of the transmittance loop. The relationship between the residual stress of as-deposited VO2 films and the relative positions between vanadium and oxygen atoms are also delineated in detail.
Effect of grain curvature on nano-indentation measurements of thin films
(2004-09-01)
Tsai, KY
;
Chin, TS
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Shieh, HPD
;
光電工程學系
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Department of Photonics
Grain curvature effect on the measurement of nano-indentation has been observed for the first time, taking VO2 thin film as an example. As the grain size of thin film is comparable to the diameter of indenter tip, the maximum penetration depths under the same maximum load (P-max) vary and lead to deviations in estimated hardness and Young's modulus. Under the same Pmax, larger penetration depth leads to a larger projected area, and a decrease in hardness. The large deviation of stiffness, affected by surface roughness under low Pmax, produces fluctuation of Young's modulus. Increase in penetration depth diminishes the roughness effect so that deviations in penetration depths dominate the variations in Young's modulus. The hardness and Young's modulus curves measured at lowest penetration depth, being thought to be free from effect of grain curvature, coincide very well to the curves measured by continuous stiffness measurements mode.
Effects of annealing on magnetic properties of new ferromagnetic semiconductor (In, Al, Mn) As
(2005-10-01)
Chen, YF
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Lee, WN
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Huang, JH
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Chin, TS
;
Guo, XJ
The effects of low-temperature (210 degrees C-290 degrees C) annealing on the microstructure, lattice constant, and magnetic properties of (In0.52Al0.48)(0.91)Mn0.09As grown by low-temperature molecular-beam epitaxy were studied. The results show that low-temperature annealing has little influence on the crystalline structure and interface quality Of (In0.52Al0.48)(0.91)Mn0.09As epilayer. In contrast, both the lattice constant and Curie temperature of (In0.52Al0.48)(0.91)Mn0.09As are found to be strongly dependent on the annealing temperature. The lattice constant linearly decreases with increasing annealing temperature; while the Curie temperature increases with increasing annealing temperature up to 250 degrees C, and then abruptly decreases upon further annealed at 270 degrees C and 290 degrees C.
(In0.52Al0.48)(1-x)MnxAs muted magnetic semiconductor grown on InP substrates
(2006-01-11)
Lee, WN
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Chen, YF
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Huang, JH
;
Guo, XJ
;
Kuo, CT
A series of diluted magnetic semiconductors, (In0.52Al0.48)(1-x)MnxAs (0 < x <= 0. 11), was successfully grown on InP substrate by low-temperature molecular beam epitaxy. Our results indicate that (In0.52Al0.48)(1-x)MnxAs exhibits interesting magnetic behaviours at 5 K: it shows paramagnetic-like behaviour when x <= 0.05 and ferromagnetic behaviour when x >= 0.06.
Optical switching properties of VO2 films driven by using WDM-aligned lasers
(2006-04-10)
Tsai, KY
;
Wu, FH
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Shieh, HPD
;
Chin, TS
;
光電工程學系
Vanadium dioxide (VO2) film had been demonstrated a high speed IR shutter driven by total optical modulation. However, it usually required a higher power heating laser of high power and precise optical systems to cover the probe beam on the sample with a heating beam of larger area. A new optical system, simply composed of wavelength division multiplexing (WDM), fiber lens or convex lens system, and a glass sheet with VO2 thin film on it, was easily assembled to utilize VO2 film as an IR shutter, implying the possibility to highly miniaturize the VO2-based optical shutter. A permanent low-transmittance (PLT) region forms on the film within the probe beam, resulting in a decrease in average power of the probe beam. Another ring-type switching area (switching ring) forms around the PLT region, resulting in the transmittance switching of the probe beam synchronously with the heating signal. VO2 films can be switched with the highest rate of a continuous square heating signal of 3 mW at 120 kHz. A heating pulse of 0.7ns and 13mW can be used to stimulate an IR pulse with fiber lens. (c) 2005 Elsevier B.V. All rights reserved.
Properties of VO2 films sputter-deposited from V2O5 target
(2003-07-01)
Tsai, KY
;
Chin, TS
;
Shieh, HPD
;
光電工程學系
;
Department of Photonics
Rutile VO2 is a thermochromic material that exhibits a reversible metal-insulator phase transition upon thermal cycling. A new deposition process of rutile VO2 from a V2O5 target was developed using reactive oxygen instead of hydrogen. Adjusting the substrate temperature and the oxygen flow ratio changes the compositions and phases of the as-deposited films into rutile VO2 under optimum deposition conditions on the Si and thick glass substrates. Crystalline phases analyzed by X-ray diffraction shows the relationship among V4O9, V6O13, and VO2 films prepared under different deposition conditions. Analysis by AFM shows that VO2 films grown at higher substrate temperatures have larger grain size. The optical switching property of VO2 was measured at a wavelength of 1.5 mum and transition temperature around 45degreesC was also measured. Inhomogeneity and the strained structure of the film are suggested to be the reasons of transition temperature lower than typical reported value because the impurity in the target is too low to be detected quantatively by ICP.