Browsing by Author "Chang, Chen-Shiung"

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Al Schottky contact on p-GaSe
(2006-10-01)
Huang, Wen-Chang
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Su, Shui-Hsiang
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Hsu, Yu-Kuei
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Wang, Chih-Chia
;
Chang, Chen-Shiung
A new Schottky diode, Al/p-GaSe, was presented in this study. It shows an effective barrier height of 0.96 eV with an ideality factor of 1.24 over five decades and a reverse leakage current density of 4.12 x 10(-7) A/cm(2) at -2 V after rapid thermal annealing at 400 degrees C for 30 s. The generation-recombination effect of the Schottky diode was decreased as the annealing temperature was increased. The formation of Al1.33Se2 was observed by X-ray diffraction analysis after the diode was annealed at 400 degrees C for 30 s. Owing to the grains' growth, the surface morphology of the 400 degrees C-annealed diode was rougher than that of the unannealed diode, which was observed both by the AFM and the SEM analysis. (c) 2006 Elsevier Ltd. All rights reserved.
Characterization of Nonlinear Optical Properties of Crystal RbGeCl(3)center dot x(H(2)O) in Infrared Region
(2009-08-01)
Tang, Li-Chuan
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Liu, Li-Qiang
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Chang, Yia-Chung
;
Yao, Jui-hsien
;
Huang, Jung-Yau
The nonlinear optical (NLO) property of hydrated rubidium germanium chloride (HRGC), RbGeCl(3)center dot x(H(2)O), is identified. Infrared absorbtion data support structural evidence that HRGC contain co-ordinated water molecules with strong hydrogen bond. The infrared spectrum indicated HRGC is transparent in most of the infrared region with only little influence from water. Calculations base on density functional theory shows that the band gap of the RbGeCl(3) (RGC) crystal is at least 3.84 eV, which is larger than that of the infrared (IR) NLO crystal CsGeCl(3). Single crystals of HRGC, sized up to 3 x 2 x 1cm(3), were grown in aqueous solution by a slow dehydrate technique. The synthetic, structural and optical propertiels of an off-centrosymmetric IR nonlinear optical (NLO) RbGeCl(3)center dot x(H(2)O) crystal were investigated experimentally. Powder second harmonic generation (PSHG) measurement indicated that the crystal structure of HRGC becomes off-centrosymmetric. Precise X-ray diffraction measurements showed that [100] family diffraction peaks split slightly. Unlike the RGC crystal structure whose space group is P2(1)(m) over bar, the HRGC crystal loses the inversion symmetry. Comparisons with known NLO material KH(2)PO(4) (KDP), indicate that HRGC's NLO susceptibility, x((2)), is about one third of that for KDP. The absorption edge of HRGC occured at 310 nm (approximate to 4.0ev), which indicated NLO HRGC crystal can have larger laser damage threshold. According to the Fourier transform infrared (FTIR) measurement, HRGC has a transparent region from 0.31 to 30 mu m, thus it can be applied to wider optical spectrum from ultraviolet, visible to mid-IR. (C) 2009 The Japan Society of Applied Physics
Characterization of Nonlinear Optical Properties of Crystal RbGeCl3 center dot x(H2O) in Infrared Region
(2009-08-01)
Tang, Li-Chuan
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Liu, Li-Qiang
;
Chang, Yia-Chung
;
Yao, Jui-hsien
;
Huang, Jung-Yau
The nonlinear optical (NLO) property of hydrated rubidium germanium chloride (HRGC), RbGeCl3 center dot x(H2O), is identified. Infrared absorbtion data support structural evidence that HRGC contain co-ordinated water molecules with strong hydrogen bond. The infrared spectrum indicated HRGC is transparent in most of the infrared region with only little influence from water. Calculations base on density functional theory shows that the band gap of the RbGeCl3 (RGC) crystal is at least 3.84 eV, which is larger than that of the infrared (IR) NLO crystal CsGeCl3. Single crystals of HRGC, sized up to 3 x 2 x 1cm(3), were grown in aqueous solution by a slow dehydrate technique. The synthetic, structural and optical propertiels of an off-centrosymmetric IR nonlinear optical (NLO) RbGeCl3 center dot x(H2O) crystal were investigated experimentally. Powder second harmonic generation (PSHG) measurement indicated that the crystal structure of HRGC becomes off-centrosymmetric. Precise X-ray diffraction measurements showed that [100] family diffraction peaks split slightly. Unlike the RGC crystal structure whose space group is P2(1)(m) over bar, the HRGC crystal loses the inversion symmetry. Comparisons with known NLO material KH2PO4 (KDP), indicate that HRGC's NLO susceptibility, x((2)), is about one third of that for KDP. The absorption edge of HRGC occured at 310 nm (approximate to 4.0ev), which indicated NLO HRGC crystal can have larger laser damage threshold. According to the Fourier transform infrared (FTIR) measurement, HRGC has a transparent region from 0.31 to 30 mu m, thus it can be applied to wider optical spectrum from ultraviolet, visible to mid-IR. (C) 2009 The Japan Society of Applied Physics
Coherent multiple-stage optical rectification terahertz wave generator
(2010-08-26)
Pan, Ci-Ling
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Huang, Jung Y.
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Chang, Chen-Shiung
;
Chen, Ching-Wei
;
Lin, Yu-Shian
The present invention coherent multiple-stage optical rectification terahertz wave generator discloses the generation of single-cycle terahertz radiation with two-stage optical rectification in GaSe crystals. By adjusting the time delay between the pump pulses employed to excite the two stages, the terahertz radiation from the second GaSe crystal can constructively superpose with the seeding terahertz field from the first stage. The high mutual coherence between the two terahertz radiation fields is ensured with the coherent optical rectification process and can be further used to synthesize a desired spectral profile of output coherent THz radiation. The technique is also useful for generating high amplitude single-cycle terahertz pulses, not limited by the pulse walk-off effect from group velocity mismatch in the nonlinear optical crystal used.
Core-Level Shift of Graphene with Number of Layers Studied by Microphotoelectron Spectroscopy and Electrostatic Force Microscopy
(2014-10-30)
Lin, Chi-Yuan
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Shiu, Hung-Wei
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Chang, Lo-Yueh
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Chen, Chia-Hao
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Chang, Chen-Shiung
The dependence of C-1s core-level shift (CLS) of graphene on the number of layer (NL) is significant information to derive the coordination-resolved C1s core-level energy (E-1s) of carbon allotropes. To observe the variation of CLS of graphene with NL, binding energy and work function of graphene with various NL were examined by scanning photoelectron microscopy/spectroscopy and electrostatic force microscopy. E1s of grounded graphene decreased as NL increased. The E-1s of single-layer graphene and multilayer graphene (MLG) is 289.42 and 289.13 eV, respectively. Based on the NL-dependent E1s of graphene, the CLS of C-1s between a free carbon atom and diamond is 0.74 eV, calculated by the bond-order-length-strength correlation theory. The CLS of graphene with NL supported the existence of surface core-level shift (SCLS) on graphite. The magnitude of SCLS in MLG was +0.09 eV. The effective coordination number is 3.68 for bilayer graphene and 4.31 for the surface carbon layer in MLG.
First Principles Calculations of Linear and Second-Order Optical Responses in Rhombohedrally Distorted Perovskite Ternary Halides, CsGeX(3) (X = Cl, Br, and I)
(2009-11-01)
Tang, Li-Chuan
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Chang, Yia-Chung
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Huang, Jung-Yau
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Lee, Ming-Hsien
;
Chang, Chen-Shiung
Systematic studies based on first-principles calculations of second. order optical susceptibilities as well as the dielectric function of CsGeX(3) (X = Cl Br, and I, CGX) are presented The relationship between structural properties and optoelectronic responses are examined The structural factors Delta alpha, and d(Ge), d(x) are proposed to describe the degree of distortion from an ideal perovskite structure. Delta alpha and dGe increase when halide anions are changed from Cl to I, while halide anion displacement, dx, decreases. The structural distortion effect on these rhombohedral CGX crystals is analyzed by first-principles calculations The dielectric function and the second harmonic generation (SHG) response coefficient also increase with increasing Delta alpha and d(Ge). The direct band gaps (E(c)) of CsGeX3 ail occur at the R-point, Delta E(R) The experimental band gaps of CGX crystals become smaller. i e, E(G)(CGI) (= 3 67eV) > E(G)(CGB) (=2 32 eV) > E(G)(CGI) (= 1 53eV), as Delta alpha and el increase, i e. d(Ge)(CGC) < d(Ge)(CGR) < d(GB)(CGI) Partial density of states (PDOS) analysis revealed that the valence band maximum (VBM) and conduction band minimum (CBM) are mainly contributed by the p-orbitals of germanium. The calculated magnitudes of chi((2))(ijk) are close to some reported experimental values near the band gap (C) 2009 The Japan Society of Applied Physics
First Principles Calculations of Linear and Second-Order Optical Responses in Rhombohedrally Distorted Perovskite Ternary Halides, CsGeX3 (X = Cl, Br, and I)
(2009-11-01)
Tang, Li-Chuan
;
Chang, Yia-Chung
;
Huang, Jung-Yau
;
Lee, Ming-Hsien
;
Chang, Chen-Shiung
Systematic studies based on first-principles calculations of second. order optical susceptibilities as well as the dielectric function of CsGeX3 (X = Cl Br, and I, CGX) are presented The relationship between structural properties and optoelectronic responses are examined The structural factors Delta alpha, and d(Ge), d(x) are proposed to describe the degree of distortion from an ideal perovskite structure. Delta alpha and dGe increase when halide anions are changed from Cl to I, while halide anion displacement, dx, decreases. The structural distortion effect on these rhombohedral CGX crystals is analyzed by first-principles calculations The dielectric function and the second harmonic generation (SHG) response coefficient also increase with increasing Delta alpha and d(Ge). The direct band gaps (E-c) of CsGeX3 ail occur at the R-point, Delta E-R The experimental band gaps of CGX crystals become smaller. i e, E-G(CGI) (= 3 67eV) > E-G(CGB) (=2 32 eV) > E-G(CGI) (= 1 53eV), as Delta alpha and el increase, i e. d(Ge)(CGC) < d(Ge)(CGR) < d(GB)(CGI) Partial density of states (PDOS) analysis revealed that the valence band maximum (VBM) and conduction band minimum (CBM) are mainly contributed by the p-orbitals of germanium. The calculated magnitudes of chi((2))(ijk) are close to some reported experimental values near the band gap (C) 2009 The Japan Society of Applied Physics
Generation and spectral manipulation of coherent terahertz radiation with two-stage optical rectification
(2008-09-01)
Chen, Ching-Wei
;
Lin, Yu-Shian
;
Huang, Jung Y.
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Chang, Chen-Shiung
;
Pan, Ci-Ling
We propose and experimentally demonstrate the generation of single-cycle terahertz radiation with two-stage optical rectification in GaSe crystals. By adjusting the time delay between the pump pulses employed to excite the two stages, the terahertz radiation from the second GaSe crystal can constructively superpose with the terahertz field injected from the first stage. The high mutual coherence between the two terahertz radiation fields is ensured with the coherent optical rectification process and can be further used to synthesize a desired spectral profile of coherent THz radiation. The technique is also potentially useful for generating high-power single-cycle terahertz pulses, usually limited by the pulse walk-off effect of the nonlinear optical crystal used. (c) 2008 Optical Society of America.
Generation properties of coherent infrared radiation in the optical absorption region of GaSe crystal
(2006-10-30)
Chen, Ching-Wei
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Hsu, Yu-Kuei
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Huang, Jung Y.
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Chang, Chen-Shiung
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Zhang, Jing-Yuan
We report a study of the effect of optical absorption on generation of coherent infrared radiation from mid-IR to THz region from GaSe crystal. The infrared-active modes of epsilon-GaSe crystal at 236 cm(-1) and 214 cm(-1) were found to be responsible for the observed optical dispersion and infrared absorption edge. Based upon phase matching characteristics of GaSe for difference-frequency generation (DFG), new Sellmeier equations of GaSe were proposed. The output THz power variation with wavelength can be properly explained with a decrease of parametric gain and the spectral profile of absorption coefficient of GaSe. The adverse effect of infrared absorption on (DFG) process can partially be compensated by doping GaSe crystal with erbium ions. (c) 2006 Optical Society of America.
Graphene On Au-Coated SiOx Substrate: Its Core-Level Photoelectron Microspectroscopy Study
(2012-08-01)
Chen, Jhih-Wei
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Wang, Chiang-Lun
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Shiu, Hung Wei
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Lin, Chi-Yuan
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Chang, Chen-Shiung
"The core-level electronic structures of exfoliated graphene sheets on a Au-coated SiOx substrate have been studied using synchrotron radiation photoelectron spectroscopy (SR-PES) on a micron scale. The graphene's visibility on the Au-coated SiOx substrate was first demonstrated by micro optical characterization, and then an SR-PES study was conducted. Because of the elimination of charging effect, a precise C 1s core-level characterization shows graphitic and contaminated carbon states of graphene. Different levels of Au-coating-induced p-type doping on single-and double-layer graphene sheets were also examined in the C 1s core-level shift. The Au-coated SiOx substrate can be treated as a simple but high-throughput platform for in situ studying graphene under further hybridization by PES. (C) 2012 The Japan Society of Applied Physics"
Hole transit in P3HT:PCBM solar cells with embedded gold nanoparticles
(2014-02-01)
Cheng, Cheng-En
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Pei, Zingway
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Hsu, Chia-Chen
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Chang, Chen-Shiung
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Chien, Forest Shih-Sen
The electrical properties of polymer solar cells (PSCs) with gold nanoparticles (AuNPs) embedded in the hole transport layers (Hits) were investigated. The PSCs with AuNP-embedded HTLs exhibited 8%, 9.5%, and 22% enhancement in short-circuit current density, open-circuit voltage, and power conversion efficiency, respectively. The low contact resistance at the active layer/Hit interface resulted in the high collection efficiency and low electron-hole recombination. The downshift of the Fermi energy in AuNP-embedded HTLs lowered the energy barrier and thinned the depletion layer at the active layer/HTL interface, accounting for the enhanced collection efficiency. (C) 2013 Elsevier B.V. All rights reserved.
Impacts of high-electroactive-surface-area buckypaper counter electrodes on the photovoltaic performance of dye-sensitized solar cells
(2015-09-09)
Cheng, Cheng-En
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Lin, Yu-Chang
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Tsai, Shang-Yi
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Lin, Zheng-Kun
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Lee, Ping-Chen
In this paper we study the photovoltaic performance of dye-sensitized solar cells (DSCs) with high-electroactive-surface-area buckypaper (BP) counter electrodes (CEs). BP is made of entangled multi-walled carbon nanotubes and has a high electroactive surface area, which is effectively 11.5 times higher than that of Pt. The high surface area of BP causes a high I-3(-) reduction rate at the CEs and suppresses the charge recombination at the anodes. Accordingly, the open-circuit voltage, the filling factor, and the power conversion efficiency of DSCs with BP CEs are enhanced, and these photovoltaic parameters exhibit a better trend with the increase of solar power compared with conventional DSCs with Pt CEs.
Improvement of the efficiency of dye-sensitized solar cells with fluorinated carbon-based liquid crystal dopant
(2017-08-01)
You, Chang-Feng
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Cheng, Cheng-En
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Lei, Bi-Cheng
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Jhang, Jia-Cih
;
Yu, Fang-Cheng
The long-term stability of dye-sensitized solar cells (DSSCs) can be improved using a liquid crystal (LC) dopant. However, the high viscosity of the LC dopant reduces the power conversion efficiency (PCE) of these cells. In this study, low-viscosity LC is doped into the DSSCs. The results indicate that the polar fluoro groups of the LCs effectively interact with the cyano groups of the organic solvent in the liquid electrolyte, enhancing the long-term stability of the DSSCs. The viscosity of the LC dopant is a key factor that affects the light-to-electrical energy conversion efficiency of the LC-doped DSSCs. The short-current density and related PCE of the DSSCs is not reduced because of the low viscosity of the doped fluorinated carbon-based LCs. (C) 2017The Physical Society of the Republic of China(Taiwan). Published by ElsevierB.V. All rights reserved.
Influences of thermal annealing on P3HT/PCBM interfacial properties and charge dynamics in polymer solar cells
(2015-12-01)
Cheng, Cheng-En
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Dinelli, Franco
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Yu, Chen-Te
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Shih, Hwa-Wei
;
Pei, Zingway
The effects of thermal annealing on the interfacial properties of poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl C-61 butyric acid methyl ester (PCBM) and on the charge dynamics in P3HT: PCBM polymer solar cells (PSCs) are investigated. This study determines that an effective phase separation of the P3HT and PCBM caused by thermal annealing achieves a larger interfacial area for efficient exciton dissociation and a well-defined pn junction with few defect levels at the P3HT/PCBM interface. Additionally, thermal annealing creates a compositional gradient across the P3HT: PCBM films, which enhances the charge transit ability significantly. These improved interfacial properties and efficiency in charge transit ability account for the better power conversion efficiency of P3HT: PCBM PSCs treated with thermal annealing. (C) 2015 The Japan Society of Applied Physics
Investigation of Graphene Dispersion From Kelly Sideband in Stable Mode-Locked Erbium-Doped Fiber Laser by Few-Layer Graphene Saturable Absorbers
(2015-11-01)
Chen, Hou-Ren
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Tsai, Chih-Ya
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Chang, Ching-Yang
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Lin, Kuei-Huei
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Chang, Chen-Shiung
In this paper, stable passively mode-locked fiber lasers (MLFLs) constructed using graphene saturable absorbers (SAs) with different layer numbers of similar to 1 to similar to 15 have been reported. The flat linear transmission spectrum in the range from 1540 to 1580 nm without any distinct absorption peak implies that the graphene SAs exhibit low dispersion in this region. Therefore, stable soliton-like pulses are generated because of negative dispersion provided by the fiber laser cavity, which requires no additional single-mode fiber (SMF) for dispersion compensation. Power-dependent transmission measurements show that the saturation intensity ranges from 1.2 to 3.2 MW/cm(2) and that the modulation depth (MD) of the graphene SAs increases with the number of graphene layers. All the samples were observed to easily mode-lock the laser with a stable mode-locking state persistently operated over hours. By analyzing the soliton Kelly sidebands, we deduced the group delay dispersion (GDD) for different layers of the graphene. The calculated results show that the variation of sample GDD is within the calculation error, indicating that the GDD of graphene is small to be negligible. This result is consistent with the experimental results reported by Chang et al. [Appl. Phys. Lett. 97, 211102 (2010)] using the phase-shift method. This study demonstrates that different layers graphene SAs have different MD contributions to the generation of laser pulses with different pulse widths.
Liquid crystal-doped liquid electrolytes for dye-sensitized solar cell applications
(2016-04-01)
Huang, Chi-Yen
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You, Chang-Feng
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Cheng, Cheng-En
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Lei, Bi-Cheng
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Jhang, Jia-Cih
We investigate the effects of liquid crystals (LCs) on the power conversion efficiency of dye-sensitized solar cells (DSSCs). The photovoltaic and electrochemical impedance spectra indicate that minute amounts of LC dopant decrease the short-current density of DSSCs because the doped LCs reduce the electrochemical reaction rate between DSSC counter electrode and electrolyte. The doped LCs delay the degradation rates of DSSCs because of the interaction between cyano groups of the doped LCs and organic solvent in the liquid electrolyte. Owing to the molecular interaction, the doped LCs increase the viscosity and stability, thereby inhibiting the evaporation rate of the liquid electrolyte. (C) 2016 Optical Society of America
Optical controlled graphene-based nonvolatile ternary-logic transistor with azobenzene copolymer
(2013-01-07)
Lin, Chi-Yuan
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Chang, Chen-Shiung
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Lin, Jian Hung
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Hsu, Chia-Chen
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Chien, Forest Shih-Sen
We demonstrated optical-controlled graphene-based nonvolatile transistors incorporated with azobenzene copolymer. The transistor was gated by the quasi remnant polarization of azobenzene copolymer, which was built by photo-assisted poling and erased by photo-depoling at room temperature. By taking the nature of polymer electret of azobenzene copolymer, the graphene-based device can perform ternary logic, and the resistance change ratio of the written status "+/- 1" to the erased status "0" was -/+ 60%. The device can retain its statuses against an electric field as high as 0.2 MV/cm because the azobenzene molecules were frozen in copolymer at room temperature. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4773984]
Optical properties and potential applications of epsilon-GaSe at terahertz frequencies
(2009-09-01)
Chen, Ching-Wei
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Tang, Tsung-Ta
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Lin, Sung-Hui
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Huang, Jung Y.
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Chang, Chen-Shiung
Ordinary and extraordinary refractive indices of an epsilon-GaSe crystal at terahertz (THz) frequencies are experimentally determined in this study. Fitting experimental data by THz time-domain spectroscopy (THz-TDS) and a Fourier transform infrared spectrometer (FTIR), we proposed revised complex dielectric functions and Sellmeier equations of GaSe for both ordinary and extraordinary waves from 0.2 to 100 THz. Phonon vibrational modes and overtones in the THz frequency range are examined in detail. The high magnitude of the figure of merit (FOM similar to 10(3) at 1 THz), the large birefringence (Delta n similar to 0.76 at 1 THz). and the low absorption coefficient (alpha similar to 0.2 cm(-1) at 1 THz) of GaSe are also identified. Potential applications to practical photonic devices such as phase shifters at THz frequencies are proposed. (C) 2009 Optical Society of America
Optical-power-dependent photodesorption kinetics of graphene studied by conductance response
(2015-06-01)
Hsu, Yang-Yang
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Lin, Chi-Yuan
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Lai, Yi-Chun
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Wu, Kun-Rui
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Ng, Kwai-Kong
The photodesorption kinetics of graphene with various UV laser power is studied by conductance response. Analytical expressions of the power-dependent photodesorption kinetics of graphene in ambience are derived. The photodesorption time constant tau(d), steady current, and magnitude of modulation current, can be expressed as functions of the adsorption time constant tau(a), desorption cross section sigma, and photon flux density. Under illumination the steady occupation ratio of adsorbed O-2 on graphene is equal to tau(d)/tau(a). It is suggested that the photodesorption of O-2 on graphene is attributed the injection of photogenerated hot electrons and is restricted by the density of antibonding states of O-2. (C) 2015 Optical Society of America
Platinum-graphene counter electrodes for dye-sensitized solar cells
(2013-07-07)
Cheng, Cheng-En
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Lin, Chi-Yuan
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Shan, Chien-Hsun
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Tsai, Shang-Yi
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Lin, Ko-Wei
This paper describes the photovoltaic performance of dye-sensitized solar cells (DSSCs) containing graphene-incorporated counter electrodes (CEs). The location and thickness of graphene in CEs are optimized to improve the photovoltaic performance of DSSCs, compared with typical Pt CEs. The DSSC, with a Pt/few-layer graphene (FLG) CE, achieved 8% in short-circuit current density and 13% in power conversion efficiency (PCE). Electrochemical impedance spectroscopy shows that the DSSC, with a Pt/FLG CE, exhibits a series resistance lower than that with a Pt CE. The lower series resistance is attributed to the contact resistance at the interface of platinum and fluorine doped tin oxide. The contact resistance is reduced by the formation of the thin platinum-carbon composite layer. It is demonstrated that the consumption of Pt could be reduced with a Pt/FLG CE. However, graphene/Pt CEs resulted in a slow charge-transfer process and consequently a worse photovoltaic performance of DSSCs. (C) 2013 AIP Publishing LLC.