Browsing by Issue Date, starting with "2006-07-26"

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Defect states investigation in poly(2-methoxy,5-(2 ' ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV)
(2006-07-26)
Nguyen, T. P.
;
Le Rendu, P.
;
Gaudin, O.
;
Lee, A. J. T.
;
Jackman, R. B.
in this study, application of the charge based Deep Level Transient Spectroscopy (Q-DLTS) has been extended to poly(2-methoxy,5-(2ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV) single layer diodes, whose cathode consisted of aluminium and anode of indium tin oxide (ITO). The results reveal a broad Q-DLTS spectrum, with at least two maxima, consistent with a complex distribution of trap states. Only the Q-DLTS maximum with the shortest relaxation time could be fully resolved over the temperature range used here (100-300 K), yielding activation energies and capture cross sections in the ranges 0.3-0.4 eV and 10(-20) 10(-18) cm(2), respectively. It will be shown that this energy level is likely related to a majority-carrier (hole) trap, consistent with a Poole-Frenkel injection mechanism and p-type doping of the MEH-PPV film. The origin of the second (non-resolved) Q-DLTS peak will also be discussed. (c) 2005 Elsevier B.V. All rights reserved.
Sub-5-fs spectroscopy of a thiophene derivative with a quinoid structure
(2006-07-26)
Kobayashi, Takayoshi
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Wang, Haibo
;
Wang, Zhuan
;
Otsubo, Tetsuo
;
電子物理學系
Sub-5-fs spectroscopy of a thiophene derivative with an electron donative and an acceptive moieties and quinoid structure provided the experimental evidence of dynamic mode coupling. It was shown that two out-of-plane bending modes mediate the dynamic mode coupling between 1469 and 1379 cm(-1) and between 1603 and 1469 cm(-1). These couplings are considered to be associated with geometrical relaxation relevant to the neutral bipolaron formation in all-s-trans polyacetylene. (c) 2006 Elsevier B.V. All rights reserved.
An adaptive bluetooth packet selection and scheduling scheme in interference environments
(2006-07-26)
Shih, Chen-Han
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Wang, Kuochen
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Shih, Hung-Cheng
;
資訊工程學系
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Department of Computer Science
Bluetooth is a new technology for Wireless Personal Area Networks (WPANs). It intends to eliminate the need of wires and connectors between a variety of devices, like PCs and their peripherals, walkmans and their earphones, etc. Bluetooth provides robust and secure wireless radio communication of both data and voice, even when the devices are not within line-of-sight. Bluetooth employs the 2.4 GHz ISM band, sharing the same band with the Wireless LAN (WLAN) implementing the IEEE 802.11 series standard. While WLANs and WPANs are complementary rather than competing technologies, the likelihood of mutual interference may occur unexpectedly, which may impact the performance of either severely. In this paper, we propose a Bluetooth channel state dependent data segmentation and reassembly (CSD-SAR) scheme and a queue state dependent priority (QSD-PR) scheduling policy. The CSD-SAR maintains a receiving frequency table to predict channel conditions and selects the best packet type and packet size to transmit data. In this way, it not only masks bad frequencies without delaying transmission but also leads to the best performance with high link utilization in error-prone environments. In addition, the QSD-PR also uses the receiving frequency table to avoid bad frequencies and gives a selected master-slave pair, which has more queued data to send between each other, a higher priority to eliminate the wastage of slots. The conventional scheduling policy, Round Robin (RR), yields poor performance with the time division duplex based MAC protocol and results in slot wastage and may not ensure fairness. Simulation results show that our proposed scheme achieves better link utilization and higher throughput with bounded delay compared to the RR scheme in error-free and error-prone environments. Our scheme can also eliminate interference to other wireless networks that share the same spectrum, such as WLANs, by avoiding selecting channels occupied by other networks. (c) 2006 Elsevier B.V. All rights reserved.
Unified semiclassical theory for the two-state system: An analytical solution for general nonadiabatic tunneling
(2006-07-28)
Zhu, Chaoyuan
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Lin, Sheng Hsien
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應用化學系
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應用化學系分子科學碩博班
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Department of Applied Chemistry
Unified semiclasical solution for general nonadiabatic tunneling between two adiabatic potential energy surfaces is established by employing unified semiclassical solution for pure nonadiabatic transition [C. Zhu, J. Chem. Phys. 105, 4159 (1996)] with the certain symmetry transformation. This symmetry comes from a detailed analysis of the reduced scattering matrix for Landau-Zener type of crossing as a special case of nonadiabatic transition and nonadiabatic tunneling. Traditional classification of crossing and noncrossing types of nonadiabatic transition can be quantitatively defined by the rotation angle of adiabatic-to-diabatic transformation, and this rotational angle enters the analytical solution for general nonadiabatic tunneling. The certain two-state exponential potential models are employed for numerical tests, and the calculations from the present general nonadiabatic tunneling formula are demonstrated in very good agreement with the results from exact quantum mechanical calculations. The present general nonadiabatic tunneling formula can be incorporated with various mixed quantum-classical methods for modeling electronically nonadiabatic processes in photochemistry. (c) 2006 American Institute of Physics.
Confined breather-type excitation in a quinoidal thiophene after sub-5 fs pulse excitation
(2006-07-28)
Kobayashi, Takayoshi
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Wang, Haibo
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Wang, Zhuan
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Otsubo, Tetsuo
;
電子物理學系
A quinoidal thiophene molecule which is a prototype of the repeated unit of s-trans-cis-polyacetylene was studied by sub-5 fs spectroscopy. A breatherlike mode modulation of both the amplitude and frequency of the C = C stretching was observed for the first time. It generates two sidebands of 2238 and 700 cm(-1) with a separation of 769 cm(-1) corresponding to the modulation frequency. The latter mode is very close to the C-S-C ring deformation, which indicate that this mode mediates coupling between the breather mode and the C-beta-C-beta stretching mode. It was also found that the breather-type excitation has a longer lifetime (2-3 ps) than in all-trans-polyacetylene (50 fs) due to its confinement. (c) 2006 American Institute of Physics.
Dynamic behaviors of dual frequency liquid crystals in bistable chiral tilted-homeotropic nematic liquid crystal cell
(2006-07-31)
Hsu, Jy-Shan
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Liang, Bau-Jy
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Chen, Shu-Hsia
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光電工程學系
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Department of Photonics
The switching behaviors of dual frequency liquid crystals (DFLC) in a bistable chiral tilted-homeotropic nematic (BHN) LC cell are simulated and compared with the observed results. This cell can be switched between tilted-homeotropic state and twisted state under the applied voltage as low as 5 V. The reason for the low switching voltage is attributed to the dielectric anisotropy character of DFLC. The analysis also shows that the switching wave form accelerates the switching behaviors of the directors which results in faster response in BHN LC cell. (c) 2006 American Institute of Physics.
Regioselectivity in the 1,3-dipolar cycloaddition of adamantylidenefulvene and its modification by inclusion in cyclodextrins' solutions
(2006-07-31)
Chu, Jean-Ho
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Li, Wan-Sheung
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Chao, Ito
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Lee, Gene-Hsiang
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Chung, Wen-Sheng
The 1,3-dipolar cycloaddition of adamantylidenefulvene (1) with 2 equiv of nitrile oxides 2a-d gave 1/1 cycloadducts, 3a-d and 4a-d, as the major products, and four other 1/2 minor cycloadducts 5-8a,b. The ratios of 1/1 cycloadducts 3a-d to 4a-d in THF solution were about 1/1 in the four different nitrile oxides 2a-d studied and microwave was found to accelerate the reactions and enhance their yields. It is noteworthy that the regioselectivity of 3a/4a was enhanced to 71/29 in beta-cyclodextrin (beta-CD) aqueous solution compared to that of 40/60 in the absence of P-CD. The regioselectivity of 3b/4b was further enhanced to 99/1 when 4-tert-butylphenyl hydroximinoyl chloride (9b) was complexed with beta-CD and then proceeded to react with 1; this is in sharp contrast with that of 33/67 in the absence of beta-CD. The binding constant of 1 center dot beta-CD in acetone-d(6)/D2O (1/1) was determined to be 188 +/- 9 M-1 by H-1 NMR titration experiments. The binding mode of 1 center dot beta-CD was further determined by ROESY experiment. Furthermore, molecular dynamic simulations were carried out to provide information of the complexation modes of 1 center dot beta-CD, 3a center dot beta-CD, 4a center dot beta-CD, 9a center dot beta-CD, and 9b center dot beta-CD. It was found that both steric and electrostatic effects play important roles in determining the regio- and stereochemistry of 1,3-dipolar cycloaddition of 1. Finally, beta-CD is shown to serve as a chiral shift reagent to differentiate the enantiomers of 4a in H-1 NMR. (c) 2006 Elsevier Ltd. All rights reserved.
Bandwidth enhancement phenomenon of a high-speed GaAs-AlGaAs based unitraveling carrier photodiode with an optimally designed absorption layer at an 830 nm wavelength
(2006-07-31)
Shi, Jin-Wei
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Li, Yu-Tai
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Pan, Ci-Ling
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Lin, M. L.
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Wu, Y. S.
In this letter, the authors introduce a GaAs/AlGaAs based unitraveling carrier photodiode (UTC-PD) for a wavelength of around 830 nm. There is significant bias- and output-current-dependent bandwidth enhancement phenomena observed with this device. According to their microwave and optical-to-electrical measurement results, such distinct phenomena can occur under a much lower current density (0.3 mA/mu m(2) vs 0.05 mA/mu m(2)) than previously reported for InP-InGaAs UTC-PDs. This can be attributed to the self-induced field in the absorption region, made possible due to the optimized p-type doping profile. (c) 2006 American Institute of Physics.
愛情萬歲
(2006-07-31)
梁玉芳
Highly efficient and stable inverted bottom-emission organic light emitting devices
(2006-07-31)
Chu, Ta-Ya
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Chen, Jenn-Fang
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Chen, Szu-Yi
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Chen, Chao-Jung
;
Chen, Chin H.
The authors report the development of highly efficient and stable C545T doped green fluorescent Alq(3) inverted bottom-emission organic light emitting device (OLED), with a device configuration of ITO/Mg/Cs(2)O:Bphen/Alq(3)/C545T:Alq(3)/NPB/WO(3)/Al, that achieved a maximum current efficiency of 23.7 cd/A and a power efficiency of 12.4 lm/W which are two times better than those of the conventional OLED. At a brightness level of 100 cd/m(2), the device required driving current density only as low as 0.5 mA/cm(2) at a driving voltage of only 5.0 V and its half-lifetime T(1/2) in excess of 104 000 h. (c) 2006 American Institute of Physics.
Enhancing luminescence efficiency of InAs quantum dots at 1.5 mu m using a carrier blocking layer
(2006-07-31)
Hsieh, Tung-Po
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Chiu, Pei-Chin
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Chyi, Jen-Inn
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Chang, Hsiang-Szu
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Chen, Wen-Yen
The authors report an effective way to enhance the optical efficiency of InAs quantum dots (QDs) on GaAs emitting at the wavelength of 1.5 mu m. It is found that the loss of holes from QDs to their proximity via the high indium composition InGaAs overgrown layer, which is necessary for achieving long wavelength emission, is the origin of photoluminescence intensity degradation at high temperature. Inserting a 4 nm thick Al0.45Ga0.55As layer, acting as a carrier blocking layer, into the GaAs capping matrix can improve the room temperature photoluminescence peak intensity by five and two times for the ground and first excited states, respectively.
Formation of germanium nanocrystals embedded in silicon-oxygen-nitride layer
(2006-07-31)
Tu, Chun-Hao
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Chang, Ting-Chang
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Liu, Po-Tsun
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Liu, Hsin-Chou
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Tsai, Chia-Chou
The formation of germanium nanocrystals embedded in silicon-oxygen nitride with distributed charge storage elements is proposed in this work. A large memory window is observed due to isolated Ge nanocrystals in the SiON gate stack layer. The Ge nanocrystals were nucleated after high temperature oxidized SiGeN layer. The nonvolatile memory with the Ge nanocrystals embedded in SiON stack layer exhibits 4 V threshold voltage shift under 10 V write operation. Also, the manufacture technology using the sequent high-temperature oxidation of the a-Si layer acting as the blocking oxide is proposed to enhance the performance of nonvolatile memory devices. (c) 2006 American Institute of Physics.
Stable inverted bottom-emitting organic electroluminescent devices with molecular doping and morphology improvement
(2006-07-31)
Chen, Szu-Yi
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Chu, Ta-Ya
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Chen, Jenn-Fang
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Su, Chien-Ying
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Chen, Chin H.
Stable inverted bottom-emitting organic light-emitting diodes (IBOLEDs) have been investigated by inserting n-type Cs2O dopant between indium-tin oxide bottom cathode and Alq(3), the combination of which not only improved the morphology of organic layer but enhanced the lifetime of the IBOLED. This n-type doped IBOLED achieved efficiencies of 5.2 cd/A and 2.0 lm/W at 20 mA/cm(2). The 20% decay lifetime (t(80)) of Cs2O doped IBOLED is 270 h which is about 1.7 times more stable than that of the conventional OLED (160 h) and 2.5 times of Li doped IBOLED (104 h). (c) 2006 American Institute of Physics.
Influence of a holey cladding structure on spectral characteristics of side-polished endlessly single-mode photonic crystal fibers
(2006-08-01)
Chen, Nan-Kuang
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Chi, Sien
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光電工程學系
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光電工程研究所
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Department of Photonics
We experimentally investigate the spectral characteristics of side-polished endlessly single-mode photonic crystal fibers of different polishing depths and radii of curvature that are important to mode field diameter. evanescent coupling, waveguide losses, higher-order mode excitation, and dispersion slopes of photonic crystal fiber components. A polished photonic crystal fiber with a greater polishing depth or a larger radius of curvature shows a more dispersive characteristic. In contrast to conventional single-mode fibers, in photonic crystal fibers the evanescent field is more strongly localized, and the propagating light can be more efficiently guided within the deformed core. (c) 2006 Optical Society of America
Hafnium silicate nanocrystal memory using sol-gel-spin-coating method
(2006-08-01)
You, Hsin-Chiang
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Hsu, Tze-Hsiang
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Ko, Fu-Hsiang
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Huang, Jiang-Wen
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Lei, Tan-Fu
The authors fabricate the hafnium silicate nanocrystal memory for the first time using a very simple sol-gel-spincoating method and 900 degrees C 1-min rapid thermal annealing (RTA). From the TEM identification, the nanocrystals are formed as the charge trapping layer after 900 degrees C 1-min RTA and the size is about 5 mn. They demonstrate the composition of nanocrystal is hafnium silicate from the X-ray-photoelectron-spectroscopy analysis. They verify the electric properties in terms of program/erase (P/E) speed, charge retention, and endurance. The sol-gel device exhibits the long charge retention time of 10(4) s with only 6% charge loss, and good endurance performance for P/E cycles up to 10(5).
Process for fabricating supersphere solid immersion lens
(2006-08-01)
Hsu
;
Wensyang
;
Sun
;
Yi-Ting
The present invention relates to process for fabricating supersphere solid immersion lens (SSIL). The procedure of the present invention comprises the steps of: firstly, coating a positive photoresist layer on a substrate, followed by first exposure and second exposure with different exposure dose separately by first mask and second mask to form the positive photoresist structure with different dimensions and depths. The first exposure dose is supplied enough to make sure the patterns of the first mask can be observed on the positive photoresist layer during the alignment of the second exposure process. And the following reflow process forms a supersphere solid immersion lens (SSIL) structure.
Simulation for optimization of mask error enhancement factor by design of experiments in both dry and immersion ArF lithography
(2006-08-01)
Yeh, Kwei-Tin
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Lin, Chih-Hung
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Hu, Ji-Ren
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Loong, Wen-An
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應用化學系
Simulations for the optimization of the mask error enhancement factor (MEEF) by using Taguchi's design of experiment (DOE) method in both dry and immersion ArF lithography have been demonstrated here. By DOE, MEEF has been successfully reduced, and the process window hash also been enlarged. Furthermore, in immersion lithography, MEEF has been significantly reduced, and resolution is also enhanced. In this study, we determined the optimal process and optical parameters to enlarge the process window and reduce MEEFs for different types of mask by DOE.
Optical coarse packet-switched IP-over-WDM network (OPSINET): Technologies and experiments
(2006-08-01)
Yuang, Maria C.
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Lee, Steven S. W.
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Tien, Po-Lung
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Lin, Yu-Min
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Shih, Julin
Optical Packet Switching (OPS) has been envisioned as a prominent future optical networking technology for data-centric IP over Wavelength Division Multiplexing (WDM) networks, or optical Internet. Such OPS technology however raises significant transport and Quality of Service QoS) challenges due to technological limitations. To circumvent OPS limitations, we have proposed a new Optical Coarse Packet Switching (OCPS) paradigm, which uses in-band-controlled per-burst switching and advocates traffic control enforcement to achieve high packet-loss performance and differentiated services. Based on OCPS, we have constructed an experimental IP-over-WDM network, referred to as OPSINET. OPSINET consists of two major types of nodes- edge routers, and Optical Label Switched Routers (OLSRs), and is facilitated with an out-of-band Generalized Multi-protocol Label Switching (GMPLS) control network. In this paper, we first introduce the OCPS paradigm. We then present the architecture of OPSINET, describe the in-band header/payload modulation technique, and detail the operations of the edge routers, OLSRs, and GMPLS control.
Synthesis and characterization of liquid-crystalline block copolymers with cyanoterphenyl moieties by atom transfer radical polymerization
(2006-08-01)
Lee, Kuan-Wei
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Wei, Kung-Hwa
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Lin, Hong-Cheu
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材料科學與工程學系
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Department of Materials Science and Engineering
A series of new mesomorphic block copolymers composed of different macroinitiators, including poly(ethylene oxide), polystyrene, and poly(ethylene oxide)-b-polystyrene, and polymethacrylate with a pendent cyanoterphenyl group were synthesized through atom transfer radical polymerization. The number-average molecular weights of the three diblock copolymers, determined by gel permeation chromatography, were 10,254, 9,772, and 15,632 g mol(-1), and their polydispersity indices were 1.17, 1.28, and 1.34. The mesomorphic and optical properties of all the block copolymers were investigated, and they possessed a smectic A phase with mesophasic ranges wider than 100 degrees C. Moreover, X-ray diffraction patterns provided evidence of the smectic A phase and the corresponding interdigitated packing of all the polymers. (c) 2006 Wiley Periodicals, Inc.
Effects of processing variables on tantalum nitride by reactive-ion-assisted magnetron sputtering deposition
(2006-08-01)
Wei, Chao-Tsang
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Shieh, Han-Ping D.
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光電工程學系
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顯示科技研究所
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Department of Photonics
The binary compound tantalum nitride (TaN) and ternary compounds tantalum tungsten nitrides (Ta1-xWxNy) exhibit interesting properties such as high melting point, high hardness, and chemical inertness. Such nitrides were deposited on a tungsten carbide (WC) die and silicon wafers by ion-beam-sputter evaporation of the respective metal under nitrogen ion-assisted deposition (IAD). The effects of N-2/Ar flux ratio, post annealing, ion-assisted deposition, deposition rate, and W doping in coating processing variables on hardness, load critical scratching, oxidation resistance, stress and surface roughness were investigated. The optimum N-2/Ar flux ratios in view of the hardness and critical load of TaN and Ta(1-x)W(x)Ny films were ranged from 0.9 to 1.0. Doping W into TaN to form Ta1-xWxPy films led significant increases in hardness' critical load, oxidation resistance, and reduced surface roughness. The optimum doping ratio was [W/(W + Ta)] = 0.85. From the deposition rate and IAD experiments, the stress in the films is mainly contributed by sputtering atoms. The lower deposition rate at a high N-2/Nr flux ratio resulted in a higher compressive stress. A high compressive residual stress accounts for a high hardness. The relatively high compressive stress Was attributed primarily to peening by atoms, ions and electrons during film growth, the Ta1-xWxNy films showed excellent hardness and strength against a high temperature, and sticking phenomena can essentially be avoided through their use. Ta1-xWxNy films showed better performance than the TaN film in terms of mechanical properties and oxidation resistance.