Browsing by Issue Date, starting with "2006-01-25"

Now showing 1 - 20 of 63786

MOCVD growth of highly strained 1.3 mu m InGaAs : Sb/GaAs vertical cavity surface emitting laser
(2006-01-25)
Chang, YA
;
Chu, JT
;
Ko, CT
;
Kuo, HC
;
Lin, CF
In0.45Ga0.55As:Sb/GaAs (1.3 mu m) vertical cavity surface emitting lasers (VCSELs) were grown by metalorganic chemical vapor deposition (MOCVD). A In0.45Ga0.55As:Sb/GaAs quantum well (QW) exhibited an emission wavelength of 1.26 mu m with narrow fullwidth at half-maximum (FWHM) of 35.9meV. For the fabricated VCSEL with 5 mu m diameter oxide-confined aperture, a room-temperature (RT).threshold current of 2.1 mA and an output power of 0.9 mW with 1.3 mu m emission were obtained. The 3 dB modulation frequency was measured to be 7.6 GHz. (c) 2005 Elsevier B.V. All rights reserved.
Quaternary AlInGaN multiple quantum well 368 nm light-emitting diode
(2006-01-25)
Wang, TC
;
Kuo, HC
;
Lee, ZH
;
Chuo, CC
;
Tsai, MY
We report high output power from AlInGaN multiple quantum well (MQW) ultraviolet light-emitting diodes. The high Al containing cladding layer, electron blocking layer and p-contact layer were chosen for transparency at 365 nm to reduce the internal absorption, reduce electron overflow and enhance output power. The UV output power was as high as 1.52 mW at 20 mA at 368 nm under room temperature CW operation. The maximum output power in CW operation is 11 mW at 170 mA. In this letter, we demonstrate a helpful and easy way to measure and calculate the junction temperature of AlInGaN UVLEDs. (c) 2005 Elsevier B.V. All rights reserved.
Structural evolution of AlN nano-structures: Nanotips and nanorods
(2006-01-25)
Shi, SC
;
Chattopadhyay, S
;
Chen, CF
;
Chen, KH
;
Chen, LC
Aluminum nitride (AIN) nanostructures were prepared using thermal chemical vapour deposition process. At growth temperatures of 950 degrees C, AIN nanotips with apex diameters of 10 nm, base diameters of similar to 100 nm, and length of similar to 2000 nm were obtained. Whereas when the growth temperature was 1200 degrees C, we obtained shorter and ihicker AIN nanorods. Compelling microscopic evidences were obtained to show that stacked AIN platelets of diminishing size formed the building blocks for the nanotips. A reducing Ehrlich-Schwoebel barrier introduced into a diffusion mediated growth model explains the formation of AIN nanorods at increasing growth temperatures. (c) 2005 Elsevier B.V. All rights reserved.
Manifestation of weak localization and long-range correlation in disordered wave functions from conical second harmonic generation
(2006-01-27)
Chen, YF
;
Su, KW
;
Lu, TH
;
Huang, KF
;
電子物理學系
We experimentally demonstrate that the near-field patterns of conical second harmonic generation of a laser in random domain structures can be used to explore the spatial structure of two-dimensional disordered wave functions with weak localization. The statistics of the experimental near-field patterns agree very well with the theoretical distributions. In addition to the short-range correlation, the localization effects are found to contribute a nearly constant value to the long-range correlation. The result of this Letter also confirms the possibility of using conical second harmonic generation as a diagnostic tool for topographical characterization of crystals.
Observation of spatially coherent polarization vector fields and visualization of vector singularities
(2006-01-27)
Chen, YF
;
Lu, TH
;
Huang, KF
;
電子物理學系
;
Department of Electrophysics
We present experimental observations of polarization vector fields from a highly isotropic microchip laser with a large Fresnel number. The experimental polarization vector field leads to complex entanglement of spatial structures and polarization states. We theoretically derive the representation of generalized coherent states to reconstruct the experimental polarization-resolved patterns. The analytical and precise reconstruction enables the vector singularities to be clearly visualized.
Fabrication of single-crystal tin nanowires by hydraulic pressure injection
(2006-01-28)
Chen, CC
;
Bisrat, Y
;
Luo, ZP
;
Schaak, RE
;
Chao, CG
Tin (Sn) nanowires, with 15 and 60 mn average diameter and up to 10 mu m in length, were fabricated by an injection process using a hydraulic pressure method. The Sn melt was injected into an anodic aluminium oxide (AAO) template and solidified to form nanowires. By back etching the aluminium substrate and barrier layer, the nanowire array ends were partially exposed from the bottom face of the AAO template. The filling ratio of nanowires inside and through the thickness of the AAO template was found to be close to 100%. The nanowires were also found to be dense and continuous with uniform diameter throughout their length. Transmission electron microscope (TEM) and x-ray diffraction (XRD) studies on the 60 nm diameter nanowires revealed that the nanowires were single crystals with body-centred-tetragonal (bct) structure predominantly growing along the [100] direction. The current method of synthesizing nanowires is straightforward, low-cost and suitable for low-melting point (< 650 degrees C) metals including low-melting point alloys with stoichiometric composition.
Triplet-triplet energy-transfer coupling: Theory and calculation
(2006-01-28)
You, ZQ
;
Hsu, CP
;
Fleming, GR
;
應用化學系分子科學碩博班
;
Institute of Molecular science
Triplet-triplet (TT) energy transfer requires two molecular fragments to exchange electrons that carry different spin and energy. In this paper, we analyze and report values of the electronic coupling strengths for TT energy transfer. Two different methods were proposed and tested: (1) Directly calculating the off-diagonal Hamiltonian matrix element. This direct coupling scheme was generalized from the one used for electron transfer coupling, where two spin-localized unrestricted Hartree-Fock wave functions are used as the zero-order reactant and product states, and the off-diagonal Hamiltonian matrix elements are calculated directly. (2) From energy gaps derived from configuration-interaction-singles (CIS) scheme. Both methods yielded very similar results for the systems tested. For TT coupling between a pair of face-to-face ethylene molecules, the exponential attenuation factor is 2.59 A(-1)(CIS/6-311+G(**)), which is about twice as large as typical values for electron transfer. With a series of fully stacked polyene pairs, we found that the TT coupling magnitudes and attenuation rates are very similar irrespective of their molecular size. If the polyenes were partially stacked, TT couplings were much reduced, and they decay more rapidly with distance than those of full-stacked systems. Our results showed that the TT coupling arises mainly from the region of close contact between the donor and acceptor frontier orbitals, and the exponential decay of the coupling with separation depends on the details of the molecular contacts. With our calculated results, nanosecond or picosecond time scales for TT energy-transfer rates are possible. (c) 2006 American Institute of Physics.
Rotational entangled states between two coupled molecules
(2006-01-28)
Liao, YY
;
Chen, YN
;
Li, CM
;
Chuu, DS
;
電子物理學系
A method is proposed to create entanglement between two coupled identical polar molecules separated at a distance of tens of nanometres. Entangled states of two coupled polar molecules controlled by half-cycle pulses are studied theoretically. The von Neumann entropy is calculated to characterize the degree of entanglement. By varying the pulse shape of the applied laser, transition from regular to irregular behaviour occurs. Moreover, the entanglement is also found to be enhanced by applying multiple laser pulses. The behaviour from quantum to classical limit is also discussed.
Semiconducting single-walled carbon nanotubes exposed to distilled water and aqueous solution: Electrical measurement and theoretical calculation
(2006-01-30)
Lu, MP
;
Hsiao, CY
;
Lo, PY
;
Wei, JH
;
Yang, YS
We fabricate and measure a single-walled carbon nanotube transistor having a liquid-gate electrode. The ratio value of I-on/I-off is as high as 10(4), indicating the presence of a semiconducting channel. A passivation layer over the source/drain electrode greatly suppresses the liquid-gate leakage by about three orders of magnitude. The channel currents are noticeably distinct between two liquid samples: distilled water and aqueous solution (1x10(-4) M NaCl). This biological sensing ability is attributed to the different electrical double-layer capacitances with respect to the bulk part of the channel. The corresponding theoretical calculation is carried out in detail. (c) 2006 American Institute of Physics.
Manufacturing method of thin film transistor
(2006-01-31)
Chang
;
Kow Ming
;
Chung
;
Yuan Hung
A method of manufacturing a thin film transistor for solving the drawbacks of the prior arts is disclosed. The method includes steps of providing an insulating substrate, sequentially forming a source/drain layer, a primary gate insulating layer, and a first conducting layer on the insulating substrate, etching the first conducting layer to form a primary gate; sequentially forming a secondary gate insulating layer and a second conducting layer on the primary gate; and etching the second conducting layer to form a first secondary gate and a second secondary gate.
雪泥
(2006-02-01)
管管
Optical properties of surface micromachining with randomly distributed etch holes
(2006-02-01)
Tien, CH
;
Lee, CH
;
光電工程學系
;
顯示科技研究所
;
Department of Photonics
Optical micromachining or microelectromechanical systems (MEMS) typically require etch holes to reduce the time required to release the micromechanical structure during the sacrificial undercutting. However, high-order diffraction beams generated by the periodic etch-hole array often deteriorate the optical performance by generating noise and erroneous crosstalk signals in. most optical systems. In this study, we examined the diffraction from a perforated micromirror and proposed a random distributed etch-hole layout. Due to the superposition of cosine functions with random periods, noise caused by high-order beams can be averaged effectively.
Memory effect on the inelastic interaction of electrons moving parallel to a solid surface
(2006-02-01)
Kwei, CM
;
Hsu, YH
;
Tu, YH
;
Tung, CJ
;
電子工程學系及電子研究所
It is generally assumed that two successive inelastic interactions between an electron and a solid are independent of each other. In other words, the electron has no memory of its previous interaction. However, the previous interaction of the electron generates a potential that should influence its succeeding inelastic interaction. The aim of this work is to establish a model to account for the memory effect of an electron between two successive inelastic interactions. On the basis of the dielectric response theory, formulae for differential inverse inelastic mean free paths (DIIMFPs) and inelastic mean free paths (IMFPs) considering the memory effect were derived for electrons moving parallel to a solid surface by solving the Poisson equation and applying suitable boundary conditions. These mean free paths were then calculated with the extended Drude dielectric function for a Cu surface. It was found that the DIIMFP and the IMFP with the memory effect for electron energy E lay between the corresponding values without the memory effect for electron energy E and previous energy Eo. The memory effect increased with increasing electron energy loss, E-0 - E-1 in the previous inelastic interaction. Copyright (c) 2005 John Wiley & Sons, Ltd.
雪泥
(2006-02-01)
管管
A compact DSP core with static floating-point arithmetic
(2006-02-01)
Lin, TJ
;
Lin, HY
;
Chao, CM
;
Liu, CW
;
Jen, CW
A multimedia system-on-a-chip (SoC) usually contains one or more programmable digital signal processors (DSP) to accelerate data-intensive computations. But most of these DSP cores are designed originally for standalone applications, and they must have some overlapped (and redundant) components with the host microprocessor. This paper presents a compact DSP for multi-core systems, which is fully programmable and has been optimized to execute a set of signal processing kernels very efficiently. The DSP core was designed concurrently with its automatic software generator based on high-level synthesis. Moreover, it performs lightweight arithmetic-the static floating-point (SFP), which approximates the quality of floating-point (FP) operations with the hardware similar to that of the integer arithmetic. In our simulations, the compact DSP and its auto-generated software can achieve 3X performance (estimated in cycles) of those DSP cores in the dual-core baseband processors with similar computing resources. Besides, the 16-bit SFP has above 40 dB signal to round-off noise ratio over the IEEE single-precision FP, and it even outperforms the hand-optimized programs based on the 32-bit integer arithmetic. The 24-bit SFP has above 64 dB quality, of which the maximum precision is identical to that of the single-precision FP. Finally, the DSP core has been implemented and fabricated in the UMC 0.18 mu m 1P6M CMOS technology. It can operate at 314.5 MHz while consuming 52mW average power. The core size is only 1.5 mmx1.5 mm including the 16 KB on-chip memory and the AMBA AHB interface.
High-reflectance composite metal coatings for planar-integrated free-space optics
(2006-02-01)
Gruber, M
;
Seiler, T
;
Wei, AC
;
光電工程學系
;
Department of Photonics
For planar-integrated free-space optical (PIFSO) systems high-reflectance thin-film coatings are crucial. Evaporated metal films are preferred for their relative technological simplicity. We propose a three-layer Al-Ag-Al coating composition that combines the high reflectance of Ag with the chemical passivity of Al and its good adherence to glass. Two special measures are taken to prevent delamination: one is an anchoring of the edges of the coating in narrow ditches that are etched into the substrate and the other is the use of an adhesive Al underlayer; to reduce absorption this underlayer is implemented only in sparsely distributed discrete areas. The optical properties of such composite coatings are investigated theoretically. The fabrication complexity is only slightly increased compared to PIFSO systems with one-layer Al reflectors. In experimental tests we verified a reflectance of approximately 98% and an adherence comparable to that of simple Al coatings. (c) 2006 Optical Society of America.
Voice over wireless local area network
(2006-02-01)
Shen, XM
;
Lin, YB
;
Pang, AC
;
Pan, JP
;
資訊工程學系
An optimal yield mapping approach for the small and medium sized liquid crystal displays
(2006-02-01)
Wang, PS
;
Su, CT
;
工業工程與管理學系
;
Department of Industrial Engineering and Management
The ability to improve yield in the manufacturing process is an important competitiveness determinant for LCD factories. The TFT-LCD contains three major manufacturing sectors: the array, cell, and module assembly processes. The yield loss from the cell process is one of the most critical steps. To increase the cell process yield, more conforming LCD panels must be produced from one glass substrate. The sorter is a robot used in LCD manufacturing systems to achieve higher yield for matching TFT and CF plates. This sorter contains several ports that can transfer CF glasses from CF cassettes to match TFT glasses. In this paper, the Hungarian method is applied to solve the yield-mapping problem with the sorter. This method provides an optimal solution to improve the cell process yield.
Study of parallel coupled-line microstrip filter in broadband
(2006-02-01)
Chen, CC
;
Kuo, JT
;
Jiang, MS
;
Chin, A
;
傳播研究所
A parallel coupled-line microstrip filter is designed and implemented on PCB with its maximum bandwidth. In this paper, this filter has presented almost very good characteristics including the simulated bandwidth of 67%. the measured bandwidth of 64%, lower insertion loss of 1.27 dB. and flat response in the pass-band. The maximum bandwidth fabricated on PCB shows good agreement with the theoretically calculated bandwidth of 70% due to the narrower gap size between the coupled lines. (C) 2005 Wiley Periodicals, Inc.
Optimisation of the GTA welding process using the Taguchi method and a neural network
(2006-02-01)
Lin, HL
;
Chou, CP
;
機械工程學系
;
Department of Mechanical Engineering
There are many parameters that affect gas tungsten arc (GTA) welding process quality. Conventionally, the Taguchi method has been widely used in engineering; however, with this method the desired results can only be obtained with the use of very discrete control factors, thus leading to uncertainty about the real optimum. In this study, the Taguchi method was used for the initial optimisation of the GTA welding process parameters. A neural network was then used to construct the relationships between the welding process parameters and weld pool geometry of each weldment. The optimal parameters of the GTA welding process were determined by simulating significant process parameters obtained by the Taguchi method. Experimental results are provided to illustrate the proposed approach.