Browsing by Author "Li, HC"

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Determination of the doping dependence of the penetration depth using YBCO microstrip ring resonators
(2001-11-01)
Gou, YS
;
Zeng, HK
;
Juang, JY
;
Lin, JY
;
Wu, KH
We present a method to determine the temperature dependent London penetration depth measured by a microstrip ring resonator for YBCO thin films with various oxygen contents. It allows us to get the following important results of the superconducting properties in the underdoped cuprate superconductors. With increasing delta (e.g. delta = 0.05, 0.2, and 0.4), the superfluid density, lambda (2)(5 K) /lambda (2)(T), is linear in the low temperature range (T < T-c/3), and the slope changes with increasing oxygen deficiency. After the temperature normalization with respect to the critical temperature, the temperature dependence of the superfluid density is shown to be independent of doping concentration. Moreover the maximum energy gap can be estimated from the model of the d-wave pairing. We found that the ratio Delta /T-c is nearly fixed value, 3.0 +/- 0.4. (C) 2001 Elsevier Science B.V. All rights reserved.
Novel poly(2,3-biphenyl-1,4-phenylenevinylene) derivatives containing long branched alkoxy and fluorenyl substituents: Synthesis, characterization, and their applications for polymer light-emitting diodes
(2005-10-18)
Chen, KB
;
Li, HC
;
Chen, CK
;
Yang, SH
;
Hsieh, BR
Two series of poly(2,3-Biphenyl-1,4-phenylenevinylene) (DP-PPV) derivatives containing long branched alkoxy chains or fluorenyl substituents were synthesized. The branched alkoxy groups were introduced to enhance the solubility for spin-coating processes. Bulky fluorenyl groups with two hexyl chains on the 9-position were introduced to increase steric hindrance and prevent close packing of the main chain. By controlling the feed ratio of different monomers during polymerization, DP-PPV derivatives with high molecular weights were obtained. All synthesized polymers possess high glass transitions temperatures and thermal stabilities. The maximum photoluminescent emissions of the thin films are located between 498 and 564 nm. Cyclic voltammetric analysis reveals that the band gaps of these light-emitting materials are in the range from 2.4 to 2.5 eV. A double-layer electroluminescent device with the configuration of ITO/PEDOT/polymer 2/Ca/Al exhibited a low turn-on voltage (4.0 V), a very high external quantum efficiency (3.39 cd/A), and a high brightness (16 910 cd/m(2)).
Superconducting NdBa2Cu3O7-delta thin films grown on bare (1(1)over-bar02) sapphire by pulsed laser deposition
(2003-05-01)
Cheng, TY
;
Lin, PI
;
Chen, SF
;
Liu, SJ
;
Juang, JY
Superconducting NdBa2Cu3O7-delta (NBCO) thin films with T-c=89 K have been. successfully grown on bare (1 (1) over bar 02) sapphire substrates by pulsed laser deposition (PLD). The X-ray diffraction results show that the as-grown NBCO films are all c-axis oriented with no observable second phase. The c-axis parameter decreases monotonically with increasing the deposition temperature (T-s), suggesting that the corresponding degradation of T-c for T-s>790degreesC might not originate from oxygen deficiency. It is conceived that the film-substrate reaction that occurring at the interface may cause Ba-deficiency and hence enhance Nd-Ba antisite substitutions.
X-ray micromachining SU-8 resist for a terahertz photonic filter
(2005-04-07)
Shew, BY
;
Li, HC
;
Pan, CL
;
Ko, CH
;
機械工程學系
Deep x-ray lithography (DXL) was used to fabricate two-dimensional photonic crystals (PCs) for a terahertz high-pass filter. Instead of the conventional poly(methyl rnethacrylate) resist, high-sensitivity SU-8 resist was used to pattern the ultra-deep (1 mm), and high aspect ratio (> 30) PC structures. In this study, an x-ray mask with thick Si membrane was used in the DXL process owing to the high-sensitivity nature of SU-8. The robust mask structure can significantly improve the fabrication yield of the conventional x-ray mask with a very thin (< 2 mu m) membrane. Preliminary results demonstrate that SU-8 has poor pattern definition after DXL process, probably due to its high sensitivity. This phenomenon can be eliminated by dissolving oxygen into the resist to 'quench' the excessive photochemical reaction. Thanks to the high adhesion property of SU-8, the sticking problem of the high aspect ratio crystals is easily solved with natural drying by reducing the unbalanced capillary force. After optimizing all the processes. the proposed DXL SU-8 technique successively fabricated the terahertz crystals with high efficiency, high precision 1(< 1 mu m) and high surface quality (R(a) similar to 12 nm). The resist pillars were then deposited with a 300 nm thick gold layer for subsequent terahertz, measurement. The measurement results show that the PC structure acts as a high-pass filter in the terahertz, range. agreeing with the simulation results.