Browsing by Issue Date, starting with "2011-01-21"

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Direct spectroscopic evidence of charge reversal at the Pb(Zr(0.2)Ti(0.8))O(3)/La(0.7)Sr(0.3)MnO(3) heterointerface
(2011-01-21)
Wu, Chung-Lin
;
Lee, Pei-Wei
;
Chen, Yi-Chun
;
Chang, Lo-Yueh
;
Chen, Chia-Hao
At the heterointerface of a top ferroelectric Pb(Zr(0.2)Ti(0.8))O(3) (PZT) ultrathin film and a bottom La(0.7)Sr(0.3)MnO(3) (LSMO) electrode, we used continuous synchrotron-radiation photoelectron spectroscopy to probe in situ and demonstrated that the interfacial charges are reversible and their affected valence-band barrier height becomes modulated upon switching the polarization in the top layer. By monitoring the core-level shifting of the buried LSMO layer under continuous illumination of synchrotron radiation, we directly observed a temporal screening of polarization induced by the photon-generated carriers in the top PZT layer. This dynamic characterization of the core-level shifting of the buried layer demonstrates an effective method to probe the electric conduction and ferroelectric polarization of an ultrathin ferroelectric oxide thin film.
Direct spectroscopic evidence of charge reversal at the Pb(Zr0.2Ti0.8)O-3/La0.7Sr0.3MnO3 heterointerface
(2011-01-21)
Wu, Chung-Lin
;
Lee, Pei-Wei
;
Chen, Yi-Chun
;
Chang, Lo-Yueh
;
Chen, Chia-Hao
At the heterointerface of a top ferroelectric Pb(Zr0.2Ti0.8)O-3 (PZT) ultrathin film and a bottom La0.7Sr0.3MnO3 (LSMO) electrode, we used continuous synchrotron-radiation photoelectron spectroscopy to probe in situ and demonstrated that the interfacial charges are reversible and their affected valence-band barrier height becomes modulated upon switching the polarization in the top layer. By monitoring the core-level shifting of the buried LSMO layer under continuous illumination of synchrotron radiation, we directly observed a temporal screening of polarization induced by the photon-generated carriers in the top PZT layer. This dynamic characterization of the core-level shifting of the buried layer demonstrates an effective method to probe the electric conduction and ferroelectric polarization of an ultrathin ferroelectric oxide thin film.
Solute-solvent intermolecular vibronic coupling as manifested by the molecular near-field effect in resonance hyper-Raman scattering
(2011-01-21)
Shimada, Rintaro
;
Hamaguchi, Hiro-o
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
Vibronic coupling within the excited electronic manifold of the solute all-trans-beta-carotene through the vibrational motions of the solvent cyclohexane is shown to manifest as the "molecular near-field effect," in which the solvent hyper-Raman bands are subject to marked intensity enhancements under the presence of all-trans-beta-carotene. The resonance hyper-Raman excitation profiles of the enhanced solvent bands exhibit similar peaks to those of the solute bands in the wavenumber region of 21 700-25 000 cm(-1) (10 850-12 500 cm(-1) in the hyper-Raman exciting wavenumber), where the solute all-trans-beta-carotene shows a strong absorption assigned to the 1A(g) -> 1B(u) transition. This fact indicates that the solvent hyper-Raman bands gain their intensities through resonances with the electronic states of the solute. The observed excitation profiles are quantitatively analyzed and are successfully accounted for by an extended vibronic theory of resonance hyper-Raman scattering that incorporates the vibronic coupling within the excited electronic manifold of all-trans-beta-carotene through the vibrational motions of cyclohexane. It is shown that the major resonance arises from the B-term (vibronic) coupling between the first excited vibrational level (v = 1) of the 1B(u) state and the ground vibrational level (v = 0) of a nearby A(g) state through ungerade vibrational modes of both the solute and the solvent molecules. The inversion symmetry of the solute all-trans-beta-carotene is preserved, suggesting the weak perturbative nature of the solute-solvent interaction in the molecular near-field effect. The present study introduces a new concept, " intermolecular vibronic coupling," which may provide an experimentally accessible/theoretically tractable model for understanding weak solute-solvent interactions in liquid. (C) 2011 American Institute of Physics. [doi:10.1063/1.3512923]
空時編碼／正交分頻多工系統中合併通道估計與資料偵測方法
(2011-01-21)
古孟霖
;
黃家齊
本發明係以最佳化方法合併通道估計及資料偵測，利用資料子載波與稀疏領航子載波追蹤通道變化；其特徵在於使用牛頓法及資料子載波達到合併通道估計及資料偵測之最佳化，並利用稀疏領航子載波所形成之最大相似函數之一階部分微分方向向量做為通道估計器追蹤通道變化之初始參考方向以得到更好的通道估計。本發明在高車行速度及大通道延遲環境下具有良好系統效能表現。
交大e-News第087期
(2011-01-21)
Secretariat
;
國立交通大學秘書室
Integration structure of semiconductor circuit and microprobe sensing elements and method for fabricating the same
(2011-01-25)
Chiou
;
Jin-Chern
;
Chang
;
Chih-Wei
The present invention discloses an integration structure of a semiconductor circuit and microprobe sensing elements and a method for fabricating the same. In the method of the present invention, a semiconductor circuit is fabricated on one surface of a semiconductor substrate, and the other surface of the semiconductor substrate is etched to form a microprobe structure for detect physiological signals. Next, a deposition method is used to sequentially form an electrical isolated layer and an electrical conductive layer on the microprobes. Then, an electrical conductive material is used to electrically connect the electrical conductive layer with the electrical pads of the semiconductor circuit. Thus is achieved the integration of a semiconductor circuit and microprobe sensing elements in an identical semiconductor substrate with the problem of electric electrical isolated being solved simultaneously. Thereby, the voltage level detected by the microprobes will not interfere with the operation of the semiconductor circuit.
Seebeck coefficients in nanoscale junctions: Effects of electron-vibration scattering and local heating
(2011-01-25)
Hsu, Bailey C.
;
Liu, Yu-Shen
;
Lin, Sheng Hsien
;
Chen, Yu-Chang
;
電子物理學系
We report first-principles calculations of inelastic Seebeck coefficients in an aluminum monatomic junction. We compare the elastic and inelastic Seebeck coefficients with and without local heating. In the low-temperature regime, the signature of normal modes in the profiles of the inelastic Seebeck effects is salient. The inelastic Seebeck effects are enhanced by the normal modes and further magnified by local heating. In the high-temperature regime, the inelastic Seebeck effects are weakly suppressed due to the quasiballistic transport.
Investigation of low-temperature electroluminescence of InGaN/GaN based nanorod light emitting arrays
(2011-01-28)
Huang, Ying-Yuan
;
Chen, Liang-Yi
;
Chang, Chun-Hsiang
;
Sun, Yu-Hsuan
;
Cheng, Yun-Wei
For InGaN/GaN based nanorod devices using a top-down etching process, the optical output power is affected by non-radiative recombination due to sidewall defects (which decrease light output efficiency) and the mitigated quantum confined Stark effect (QCSE) due to strain relaxation (which increases internal quantum efficiency). Therefore, the exploration of low-temperature optical behaviors of nanorod light emitting diodes (LEDs) will help identify the correlation between these two factors. In this work, low-temperature electroluminescent (EL) spectra of InGaN/GaN nanorod arrays were explored and compared with those of planar LEDs. The nanorod LED exhibits a much higher optical output percentage increase when the temperature decreases. The increase is mainly attributed to the increased carriers in the quantum wells for radiative recombination. Also, due to a better spatial overlap of electrons and holes in the quantum wells, the increased number of carriers can be more efficiently recombined in the nanorod device. Next, while the nanorod array shows nearly constant peak energy in the EL spectra at various injection currents at the temperature of 300 K, a blue shift has been observed at 190 K. The results suggest that with less non-radiative recombination and thus more carriers in the quantum wells, carrier screening and band filling still prevail in the partially strain relaxed nanorods. Moreover, when the temperature drops to 77 K, the blue shift of both nanorod and planar devices disappears and the optical output power decreases since there are fewer carriers in the quantum wells for radiative recombination.
Association structures of ionic liquid/DMSO mixtures studied by high-pressure infrared spectroscopy
(2011-01-28)
Jiang, Jyh-Chiang
;
Lin, Kuan-Hung
;
Li, Sz-Chi
;
Shih, Pao-Ming
;
Hung, Kai-Chan
Using high-pressure infrared methods, we have investigated close interactions of charge-enhanced C-H-O type in ionic liquid/dimethyl sulfoxide (DMSO) mixtures. The solvation and association of the 1-butyl-3-methylimidazolium tetrafluoroborate (BMI(+)BF(4)(-)) and 1-butyl-2,3-dimethylimidazolium tetrafluoroborate (BMM(+)BF(4)(-)) in DMSO-d(6) were examined by analysis of C-H spectral features. Based on our concentration-dependent results, the imidazolium C-H groups are more sensitive sites for C-H-O than the alkyl C-H groups and the dominant imidazolium C-H species in dilute ionic liquid/DMSO-d(6) should be assigned to the isolated (or dissociated) structures. As the dilute mixtures were compressed by high pressures, the loss in intensity of the bands attributed to the isolated structures was observed. In other words, high pressure can be used to perturb the association-dissociation equilibrium in the polar region. This result is remarkably different from what is revealed for the imidazolium C-H in the BMM(+)BF(4)(-)/D(2)O mixtures. DFT-calculations are in agreement with our experimental results indicating that C(4)-H-O and C(5)-H-O interactions seem to play non-negligible roles for BMM(+)BF(4)(-)/DMSO mixtures. (C) 2011 American Institute of Physics. [doi:10.1063/1.3526485]
Molecular structural property and potential energy dependence on nonequilibrium-thermodynamic state point of liquid n-hexadecane under shear
(2011-01-28)
Tseng, Huan-Chang
;
Chang, Rong-Yeu
;
Wu, Jiann-Shing
;
應用化學系
;
Department of Applied Chemistry
Extensive computer experiments have been conducted in order to shed light on the macroscopic shear flow behavior of liquid n-hexadecane fluid under isobaric-isothermal conditions through the nonequilibrium molecular dynamic methodology. With respect to shear rates, the accompanying variations in structural properties of the fluid span the microscopic range of understanding from the intrinsic to extrinsic characteristics. As drawn from the average value of bond length and bond angle, the distribution of dihedral angle, and the radius distribution function of intramolecular and intermolecular van der Waals distances, these intrinsic structures change with hardness, except in the situation of extreme shear rates. The shear-induced variation of thermodynamic state curve along with the shear rate studied is shown to consist of both the quasiequilibrium state plateau and the nonequilibrium-thermodynamic state slope. Significantly, the occurrence of nonequilibrium-thermodynamic state behavior is attributed to variations in molecular potential energies, which include bond stretching, bond bending, bond torsion, and intra-and intermolecular van der Waals interactions. To unfold the physical representation of extrinsic structural deformation, under the aggressive influence of a shear flow field, the molecular dimension and appearance can be directly described via the squared radius of gyration and the sphericity angle, R(g)(2) and phi, respectively. In addition, a specific orientational order S(x) defines the alignment of the molecules with the flow direction of the x-axis. As a result, at low shear rates, the overall molecules are slightly stretched and shaped in a manner that is increasingly ellipsoidal. Simultaneously, there is an obvious enhancement in the order. In contrast to high shear rates, the molecules spontaneously shrink themselves with a decreased value of R(g)(2), while their shape and order barely vary with an infinite value of phi and S(x). It is important to note that under different temperatures and pressures, these three parameters are integrated within a molecular description in response to thermodynamic state variable of density and rheological material function of shear viscosity. (C) 2011 American Institute of Physics. [doi:10.1063/1.3541825]
Compact microdisk cavity laser with type-II GaSb/GaAs quantum dots
(2011-01-31)
Hsu, K. S.
;
Chiu, T. T.
;
Lin, Wei-Hsun
;
Chen, K. L.
;
Shih, M. H.
Microdisk lasers with active region made of type-II GaSb/GaAs quantum dots on the GaAs substrate have been demonstrated. A microdisk cavity with diameter of 3.9 mu m was fabricated from a 225-nm-thick GaAs layer filled with GaSb quantum dots. Lasing at wavelengths near 1000 nm at 150 K was achieved for this microdisk. A high threshold characteristic temperature of 77 K was also observed. It is found that the lasing wavelength matches closely with the first-order whispering-gallery mode of the cavity as obtained from the finite-element method simulation. (c) 2011 American Institute of Physics. [doi: 10.1063/1.3543839]
A reflective polarizer-free electro-optical switch using dye-doped polymer-stabilized blue phase liquid crystals
(2011-01-31)
Lin, Yi-Hsin
;
Chen, Hung-Shan
;
Chiang, Tsung-Han
;
Wu, Chun-Hung
;
Hsu, Hsu-Kuan
We demonstrate a reflective polarizer-free electro-optical switch using dye-doped polymer-stabilized blue phase liquid crystals (DDPSBP-LC). At the voltage-off state, the dye molecules and liquid crystals form the structure of the double twist cylinders. As a result, the DDPSBP-LC is in dark state due to the combination of Bragg reflection and light absorption. At the voltage-on state, the blue phase structure is unwound locally. The DDPSBP-LC is then in bright state because of the small light absorption only. The applications of such a switch are shutter glass of 3D displays, and electronic papers. (C) 2011 Optical Society of America
Stacked GeO/SrTiO(x) Resistive Memory with Ultralow Resistance Currents
(2011-01-31)
Cheng, C. H.
;
Chin, Albert
;
Yeh, F. S.
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We report a high performance and low-power operated resistive memory. Using stacked covalent-bond-dielectric GeO(x) on metal-oxide SrTiO(x) to form the cost-effective Ni/GeO(x)/SrTiO(x)/TaN resistive random access memory, ultralow set power of small 1 mu W (0.9 mu A at 1.2 V), reset power of 13 pW (0.13 nA at 0.1 V), fast 50 ns switching time and good 10(6) cycling endurance are realized. (C) 2011 American Institute of Physics. [doi:10.1063/1.3549689]
Implementation issues of the nearfield equivalent source imaging microphone array
(2011-01-31)
Bai, Mingsian R.
;
Lin, Jia-Hong
;
Tseng, Chih-Wen
;
機械工程學系
;
Department of Mechanical Engineering
This paper revisits a nearfield microphone array technique termed nearfield equivalent source imaging (NESI) proposed previously. In particular, various issues concerning the implementation of the NESI algorithm are examined. The NESI can be implemented in both the time domain and the frequency domain. Acoustical variables including sound pressure, particle velocity, active intensity and sound power are calculated by using multichannel inverse filters. Issues concerning sensor deployment are also investigated for the nearfield array. The uniform array outperformed a random array previously optimized for far-field imaging, which contradicts the conventional wisdom in far-field arrays. For applications in which only a patch array with scarce sensors is available, a virtual microphone approach is employed to ameliorate edge effects using extrapolation and to improve imaging resolution using interpolation. To enhance the processing efficiency of the time-domain NESI, an eigensystem realization algorithm (ERA) is developed. Several filtering methods are compared in terms of computational complexity. Significant saving on computations can be achieved using ERA and the frequency-domain NESI, as compared to the traditional method. The NESI technique was also experimentally validated using practical sources including a 125 cc scooter and a wooden box model with a loudspeaker fitted inside. The NESI technique proved effective in identifying broadband and non-stationary sources produced by the sources. (C) 2010 Elsevier Ltd. All rights reserved.
Nitrogenated amorphous InGaZnO thin film transistor
(2011-01-31)
Liu, Po-Tsun
;
Chou, Yi-Teh
;
Teng, Li-Feng
;
Li, Fu-Hai
;
Shieh, Han-Ping
This work presents the electrical characteristics of the nitrogenated amorphous InGaZnO thin film transistor (a-IGZO:N TFT). The a-IGZO: N film acting as a channel layer of a thin film transistor (TFT) device was prepared by dc reactive sputter with a nitrogen and argon gas mixture at room temperature. Experimental results show that the in situ nitrogen incorporation to IGZO film can properly adjust the threshold voltage and enhance the ambient stability of a TFT device. Furthermore, the a-IGZO: N TFT has a 44% increase in the carrier mobility and electrical reliability and uniformity also progress obviously while comparing with those not implementing a nitrogen doping process. (C) 2011 American Institute of Physics. [doi:10.1063/1.3551537]
A facile route to prepare PdPt alloys for ethanol electro-oxidation in alkaline electrolyte
(2011-01-31)
Lin, Sheng-Chieh
;
Chen, Jing-Yu
;
Hsieh, Yi-Fan
;
Wu, Pu-Wei
;
材料科學與工程學系
We adopted a displacement reaction in acidic solution that enabled the spontaneous reduction of Pd and Pt cations in conjunction with corrosive dissolution of Ni. The composition for the PdPt was adjusted by varying the concentration of Pd and Pt cations. From SEM images and XRD patterns, the PdPt formed an fcc alloy uniformly deposited on the Ni substrate. Electro-oxidation of ethanol was conducted in alkaline electrolyte for samples of Pd, Pt, and PdPt alloys. In cyclic voltammetric profiles, the Pd(77)Pt(23) revealed the highest electrocatalytic ability in both apparent current and mass activity, followed by Pd(87)Pt(13), Pd, and Pt. Similar behaviors were observed in life time measurements in which stable performances for ethanol electro-oxidation were obtained. (C) 2010 Elsevier B.V. All rights reserved.
Vertical polymer phototransistor featuring photomultiplication due to base-field shielding
(2011-01-31)
Zan, Hsiao-Wen
;
Tsai, Wu-Wei
;
Meng, Hsin-Fei
;
物理研究所
;
光電工程學系
We introduce a vertical polymer phototransistor with low operational voltage (-1.5 V). A blended polymer layer with both acceptor and donor materials was used as a channel material in the vertical space-charge-limited transistor. Under illumination, we obtained external quantum efficiency (EQE) as high as 360% at 620 nm. We propose the effects of base-field shielding as a means to explain high EQE. This proposition has been supported by two-dimensional simulation of the device. (C) 2011 American Institute of Physics. [doi:10.1063/1.3552714]
Stacked GeO/SrTiOx Resistive Memory with Ultralow Resistance Currents
(2011-01-31)
Cheng, C. H.
;
Chin, Albert
;
Yeh, F. S.
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We report a high performance and low-power operated resistive memory. Using stacked covalent-bond-dielectric GeOx on metal-oxide SrTiOx to form the cost-effective Ni/GeOx/SrTiOx/TaN resistive random access memory, ultralow set power of small 1 mu W (0.9 mu A at 1.2 V), reset power of 13 pW (0.13 nA at 0.1 V), fast 50 ns switching time and good 10(6) cycling endurance are realized. (C) 2011 American Institute of Physics. [doi:10.1063/1.3549689]
2-Step self-assembly method to fabricate broadband omnidirectional antireflection coating in large scale
(2011-02-01)
Yeung, K. M.
;
Luk, W. C.
;
Tam, K. C.
;
Kwong, C. Y.
;
Tsai, M. A.
We have developed a simple and reproducible 2-step self-assembly method for the fabrication of broadband, omnidirectional antireflection coating on glass substrate with 4 in. size. The glass surface has been modified to be positively charged, then the negatively charged nano silica is self-assembled to the glass substrate by electrostatic attraction. The nanostructure on the glass substrate reduces the reflection significantly, which results in enhanced transmittance. Transmittance as high as 97.7% at 499 nm has been obtained for a double-side coated glass substrate. Obvious reduction in weighted reflectance is still observed up to 60 degrees incident angle. (C) 2010 Elsevier B.V. All rights reserved.
Investigation of the Atmospheric Helium Dielectric Barrier Discharge Driven by a Realistic Distorted-Sinusoidal Voltage Power Source
(2011-02-01)
Hung, C. -T.
;
Chiu, Y. -M.
;
Hwang, F. -N.
;
Chiang, M. -H.
;
Wu, J. -S.
The non-equilibrium atmospheric-pressure parallel-plate helium dielectric barrier discharge (DBD) driven by a realistic 20 kHz distorted-sinusoidal voltage waveform has been investigated by means of simulations and experiments. A self-consistent one-dimensional fluid modeling code considering the non-local electron energy balance was applied to simulate the helium DBD. The effect of selecting plasma chemistry was investigated by comparing simulations with experiments. The results show that the simulations, which include more excited helium, metastable helium and electron-ion-related reaction channels, can faithfully reproduce the measured discharged temporal current quantitatively. Based on the simulated discharge properties, we have found that there is complicated mode transition of discharges from the long Townsend-like to the "dark current"-like, then to the short primary Townsend-like and the short secondary Townsend-like for the helium DBD that is driven by a realistic distorted-sinusoidal voltage power source. Discharge properties in different periods of discharge are discussed in detail in the paper.