Browsing by Issue Date, starting with "2003-04-20"

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古硯
(2003-04-20)
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(2003-04-20)
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(2003-04-20)
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(2003-04-20)
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(2003-04-20)
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(2003-04-20)
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(2003-04-20)
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Current detection of superradiance and induced entanglement of double quantum dot excitons
(2003-04-25)
Chen, YN
;
Chuu, DS
;
Brandes, T
;
電子物理學系
;
Department of Electrophysics
We propose to measure the superradiance effect by observing the current through a semiconductor double-dot system. An electron and a hole are injected separately into one of the quantum dots to form an exciton and then recombine radiatively. We find that the stationary current shows oscillatory behavior as one varies the interdot distance. The amplitude of oscillation can be increased by incorporating the system into a microcavity. Furthermore, the current is suppressed if the dot distance is small compared to the wavelength of the emitted photon. This photon trapping phenomenon generates the entangled state and may be used to control the emission of single photons at predetermined times.
Theory of the vortex matter transformations in high-T-c superconductor YBCO
(2003-04-25)
Li, DP
;
Rosenstein, B
;
交大名義發表
;
電子物理學系
;
National Chiao Tung University
Flux line lattice in type II superconductors undergoes a transition into a "disordered" phase such as vortex liquid or vortex glass, due to thermal fluctuations and random quenched disorder. We quantitatively describe the competition between the thermal fluctuations and the disorder using the Ginzburg-Landau approach. The following T-H phase diagram of YBCO emerges. There are just two distinct thermodynamical phases, the homogeneous and the crystalline one, separated by a single first order transition line. The line, however, makes a wiggle near the experimentally claimed critical point at 12 T. The "critical point" is reinterpreted as a (noncritical) Kauzmann point in which the latent heat vanishes and the line is parallel to the T axis. The magnetization, the entropy, and the specific heat discontinuities at melting compare well with experiments.
An assessment of the effect of sea surface surfactant on global atmosphere-ocean CO2 flux
(2003-04-26)
Tsai, WT
;
Liu, KK
;
土木工程學系
;
Department of Civil Engineering
[1] We assess the possible impact of the distribution of naturally occurring surfactants on the direct integration of the global atmosphere-ocean CO2 flux across the ocean surface. The global atmosphere-ocean CO2 flux is calculated using the monthly mean DeltapCO(2) climatology compiled by Takahashi et al. [1997] as well as satellite wind speed and sea-surface temperature data. In the absence of any global map of surfactant coverage and as it is known that phytoplankton exudates and degradation products are the major sources of marine surfactants, ocean primary productivity, which can be derived from the satellite-based estimate of chlorophyll concentration, is used as an indicator of the presence of surfactants as proposed by Asher [1997]. From the calculated results it is found that suppression of the upward and downward CO2 fluxes by marine surfactants exhibits an asymmetric effect: The average percent reduction of absorption flux by surfactants is about twice that of outgassing, which results in an overall decrease in the net global CO2 uptake by the oceans. For almost half of the year (between January and May) the presence of surfactants does not affect CO2 outgassing from global oceans. In contrast, throughout the entire year the presence of surfactants suppresses CO2 absorption by the oceans. The major reduction in absorption fluxes occurs in the northern Pacific and Atlantic (10degreesN to 70degreesN) in all seasons and in the Southern Ocean (south of 40degreesS) in austral spring and summer. However, the most significant decrease in outgassing fluxes occurs in the equatorial and southern Pacific Ocean (40degreesS to 10degreesN), particularly in the eastern equatorial and subtropical waters off the southern American coast, in the period of austral spring and summer. Annual net CO2 flux is reduced by approximately 20% under the surfactant coverage condition that the primary productivity is above a threshold value of 25 g-C m(-2) mom(-1) and by about 50% with a threshold of 15 g-C m(-2) mom(-1).
Self-organized titanium oxide nanodot arrays by electrochemical anodization
(2003-04-28)
Chen, PL
;
Kuo, CT
;
Tsai, TG
;
Wu, BW
;
Hsu, CC
Ordered nanodot arrays of titanium oxides were prepared from TiN/Al films on the silicon substrate by electrochemical anodization of a TiN layer using a nanoporous anodic aluminum oxide film as the template. The microstructure of the nanodot arrays was studied by transmission electron microscopy and scanning electron microscopy, and the chemical composition of nanodots was analyzed by electron energy loss spectroscopy. The as-prepared nanodots are basically composed of amorphous TiOx with a hexagonal arrangement and an average diameter of about 60 nm. Using this approach, it is expected that nanodot arrays of various oxide semiconductors can be achieved. (C) 2003 American Institute of Physics.
Liquid phase deposited SiO2 on GaN
(2003-04-29)
Wu, HR
;
Lee, KW
;
Nian, TB
;
Chou, DW
;
Wu, JJH
An efficient and low cost approach to deposit uniform silicon dioxide layers on GaN by liquid phase deposition (LPD) near room temperature are described and discussed. The process is simple. GaN wafers are immersed into a H2SiF6 and H3BO3 solution to form the silicon dioxide layers. The deposition conditions and the properties of the SiO2 films will be characterized. (C) 2002 Elsevier Science B.V. All rights reserved.
Temperature dependent integrity of Sr0.8Bi2Ta2O9 films on ultra-thin Al2O3 buffered Si
(2003-04-29)
Lan, BC
;
Chen, SY
;
Lee, HY
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The annealing temperature dependent integrity of Sr0.8Bi2Ta2O9 (SBT) on ultra-thin 4 nm SiO2 and Al2O3 buffered Si was investigated in this work. Although the capacitance-voltage characteristics show hysteresis loops in both cases, the memory window of Sr0.8Bi2Ta2O9/Al2O3 capacitor is larger than that of Sr0.8Bi2Ta2O9/SiO2 capacitor. As increasing annealing temperature from 800 to 900degreesC, the grain size and memory window of polycrystalline SBT increase both cases. At 800degreesC, the leakage current density of Sr0.8Bi2Ta2O9/Al2O3 capacitor is 3.2 x 10(-8) A/cm(2) at -3V, which is low enough for deep sub-mum application. With increasing temperature to 900degreesC, the leakage current in both structures becomes smaller. (C) 2002 Elsevier Science B.V. All rights reserved.
Integrating mobile IP with ad hoc networks
(2003-05-01)
Tseng, YC
;
Shen, CC
;
Chen, WT
;
交大名義發表
;
National Chiao Tung University
The Internet Engineering Task Force's mobile Internet protocol uses mobile agents to support. seamless handoffs, making it possible for mobile hosts to roam from subnet to subnet without changing IP addresses. Another emerging wireless architecture, mobile ad hoc networks (Manets), can be flexibly deployed in most environments without the need for infrastructure base stations. Integrating these two architectures will facilitate the current trend of moving to an all-IP wireless environment. By supporting greater roaming flexibility, the authors propose integrating mobile IP with Manets to realize the dream of broadband wireless Internet access.
Enhanced negative substrate bias degradation in nMOSFETs with ultrathin plasma nitrided oxide
(2003-05-01)
Perng, TH
;
Chien, CH
;
Chen, CW
;
Lin, HC
;
Chang, CY
The degradation induced by substrate hot electron (SHE) injection in 0.13-mum nMOSFETs with ultrathin (similar to2.0 - nm) plasma nitrided gate dielectric was studied. Compared to the conventional thermal oxide, the ultrathin nitrided gate dielectric is found to be more vulnerable to SHE stress, resulting in enhanced threshold voltage (V-t) shift and transconductance (G(m)) reduction. The severity of the enhanced degradation increases with increasing nitrogen content in gate dielectric with prolonged nitridation time. While the SHE-induced degradation is found to be strongly related to the injected electron energy for both conventional oxide [1], [2]and plasma-nitrided oxide, dramatic degradation in threshold voltage shift for nitrided oxide is found to occur at a lower substrate bias magnitude (- - 1 V), compared to thermal oxide (similar to -1.5 V). This enhanced degradation by negative substrate bias in nMOSFETs with plasma-nitrided gate dielectric is attributed to a higher concentration of paramagnetic electron trap precursors introduced during plasma nitridation [3].
Oscillations of magnetoconductance in semiconductor-superconductor junctions with a laterally potential barrier isolator inside semiconductor region
(2003-05-01)
Yang, TJ
;
Hsue, YC
;
Gu, BY
;
電子物理學系
;
Department of Electrophysics
Magnetoconductance (MC) injunctions of a superconductor and a semiconductor (Sm) consisting of two parallel quantum waveguides (QW) coupled through a potential barrier under a perpendicular applied magnetic field in the semiconductor region is studied theoretically. The results of MC showing a series of oscillations with stepwise platform and spikes may be understood well within the phenomenological argument similar to Y. Asano (Phys. Rev. B 61 (2000) 1732) proposed. The oscillatory peaks of the MC in the dual QW are found essentially due to the variation of the number of the propagation modes. (C) 2003 Elsevier Science B.V. All rights reserved.
Calculations of the inter-subband scattering rates of electrons in GaAs/AlGaAs quantum wells
(2003-05-01)
Lee, HC
;
Sun, KW
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
In this presentation, we report the calculated results on hot electron relaxation through inter- and intra-subband scatterings with LO phonons in quantum well structures. The scattering rates were calculated for electrons excited both in the gamma valley and L valleys. The types of optical phonons adapted in our model are determined based on the dielectric continuum model. We have also studied the dependence of the scatterings on the structure parameters of the quantum well. (C) 2003 Elsevier Science Ltd. All rights reserved.
Correlation between dewatering index and dewatering performance of three mechanical dewatering devices
(2003-05-01)
Pan, JRS
;
Huang, CP
;
Cherng, MY
;
Li, KC
;
Lin, CF
Efficient sludge conditioning can improve sludge dewatering characteristics and promote the separation of flocs from the liquid phase to achieve a high solid content. To optimize this process, a reliable dewatering index must be established. Although numerous researches investigated sludge conditioning, few are devoted to the correlation between the conditioning index and the dewatering efficiency. In this study, sludges were conditioned with both synthetic and natural polymers, and their dewatering characteristics after three different mechanical dewatering devices, the filter press, belt press, and the centrifuge, were compared. The result shows that the traditionally used dewatering index may not reflect sludge conditioning properly. Correlation between sludge conditioning indices and dewaterability depends upon both the type of sludge and the means of sludge conditioning and dewatering. It is therefore concluded that dewatering index must be properly chosen for optimum sludge conditioning. (C) 2002 Elsevier Science Ltd. All rights reserved.
Adaptive approaches to relieving broadcast storms in a wireless multihop mobile ad hoc network
(2003-05-01)
Tseng, YC
;
Ni, SY
;
Shih, EY
;
資訊工程學系
;
Department of Computer Science
In a multihop mobile ad hoc network, broadcasting is an elementary operation to support many applications. In [15], it is shown that naively broadcasting by flooding may cause serious redundancy, contention, and collision in the network, which we refer to as the broadcast storm problem. Several threshold-based schemes are shown to perform better than flooding in that work. However, how to choose thresholds also poses a dilemma between reachability and efficiency under different host densities. In this paper, we propose several adaptive schemes, which can dynamically adjust thresholds based on local connectivity information. Simulation results show that these adaptive schemes can offer better reachability as well as efficiency as compared to the results in [15].
Peculiar hole doping by Ca substitution in cuprate superconductors
(2003-05-01)
Lin, JY
;
Chung, PC
;
Liu, SJ
;
Hsiang, CC
;
Lin, PH
The doping effect of Ca substitution in Y0.7Ca0.3Ba2Cu3Oy has been studied for y=6.9 and 6 by the x-ray absorption near edge spectroscopy (XANES). While Ca doping leads to an obvious increase in hole concentration in the CuO2 planes in Y0.7Ca0.3Ba2Cu3O6.9, XANES indicates absence of this doping effect in Y0.7Ca6.3Ba2Cu3O6. These two contradict results suggest that the doping effect by Ca substitution could be sensitive to the oxygen content when y similar to6.0. Comparisons with others' works are made.