Browsing by Author "Lin, H. J."

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A comprehensive study of temperature-dependent reflectance and photoluminescence of Zn(1-x)Mn(x)O thin films grown on c-Al(2)O(3)
(2009-03-01)
Lin, D. Y.
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Lin, H. J.
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Wu, J. S.
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Chou, W. C.
;
Yang, C. S.
We present a systematic study of temperature-dependent reflectance (R) and photoluminescence (PL) measurements on ZnMnO films grown by plasma-assisted molecular beam epitaxy. For the first time, the three free-exciton transitions FX(A) (Gamma(7c)-Gamma(u)(7v)), FX(B) (Gamma(7c)-Gamma(9v)), and FX(C) (Gamma(7c)-Gamma(l)(7v)) and the longitudinal-optical phonon replicas of FX(B) and FX(C) of ZnMnO films have been clearly observed in the R spectra. The parameters describing the activation energy and the temperature dependence of the transition energy and broadening have been extracted by fitting the experimental R and PL spectra. The spectral data of ZnMnO films not only show the deterioration of crystalline quality with increasing Mn composition fraction but also indicate the Mn clustering caused by Mn atom segregation.
A comprehensive study of temperature-dependent reflectance and photoluminescence of Zn1-xMnxO thin films grown on c-Al2O3
(2009-03-01)
Lin, D. Y.
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Lin, H. J.
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Wu, J. S.
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Chou, W. C.
;
Yang, C. S.
We present a systematic study of temperature-dependent reflectance (R) and photoluminescence (PL) measurements on ZnMnO films grown by plasma-assisted molecular beam epitaxy. For the first time, the three free-exciton transitions FXA (Gamma(7c)-Gamma(u)(7v)), FXB (Gamma(7c)-Gamma(9v)), and FXC (Gamma(7c)-Gamma(l)(7v)) and the longitudinal-optical phonon replicas of FXB and FXC of ZnMnO films have been clearly observed in the R spectra. The parameters describing the activation energy and the temperature dependence of the transition energy and broadening have been extracted by fitting the experimental R and PL spectra. The spectral data of ZnMnO films not only show the deterioration of crystalline quality with increasing Mn composition fraction but also indicate the Mn clustering caused by Mn atom segregation.
Comparison of MiM performance with various electrodes and dieletric in Cu dual damascene of CMOS MS/RF technology
(2006)
King, M. C.
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Chang, C. F.
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Lin, H. J.
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Chin, Albert
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電子工程學系及電子研究所
In this paper, we have compared the performance of metal-insulator-metal (MiM) capacitors for different bottom electrode materials including Cu, TaN, and Al in Cu-back-end-of-the-line (BEOL) process. A high-performance and low-defect-density MiM capacitor for mixed-signal and radio frequency (MS/RF) technology based on a 130 nm complementary metal oxide semiconductor (CMOS) process was demonstrated. Q-factor can achieve > 100 for both Cu and Al at 2.4 GHz with 0.7 pF MiM capacitors. TaN showed a low Q-factor (< 60) due to high resistivity. The process incorporates aluminum electrode into Cu BEOL for MiM capacitor with a cost-effective process. The roughness of electro-dielectric interface by a thin aluminum electrode is critical for MiM performance due to field enhancement by roughness of a thin aluminum electrode. We have demonstrated a way to eliminate the roughness effect of thin Al and provide a MiM capacitor with high performance and low defect density. In particular, a method is demonstrated to achieve better matching, leakage, electrical breakdown, and temperature coefficient of capacitance performance for MiM capacitors. (c) 2006 The Electrochemical Society.
Determination of the microstructure of Eu-treated ZnO nanowires by x-ray absorption
(2010-02-08)
Huang, W. L.
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Labis, J.
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Ray, S. C.
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Liang, Y. R.
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Pao, C. W.
X-ray absorption near-edge structure (XANES), extended x-ray absorption fine structures (EXAFS), and photoluminescence measurements were used to elucidate the microstructural and photoluminescence properties of ZnO nanowires (ZnO-NWs) that had been treated with Eu by thermal diffusion. The O K- and Eu L(3)-edge XANES and EXAFS spectra at the Zn K- and Eu L(3)-edge verified the formation of Eu(2)O(3)-like layer on the surface of ZnO-NWs. X-ray diffraction, XANES and EXAFS measurements consistently suggest the lack of substitutional doping of Eu ions at the Zn ion sites in the interior of ZnO-NWs. The clear sharp and intense emission bands in the range 610-630 nm of Eu-treated ZnO-NWs originated from the intra-4f transition of Eu ions in the Eu(2)O(3)-like surface layer.
Effect of geometry on the magnetic properties of CoFe2O4-PbTiO3 multiferroic composites
(2013)
Wang, B. Y.
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Wang, H. T.
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Singh, Shashi B.
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Shao, Y. C.
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Wang, Y. F.
In this study, X-ray absorption near-edge structure (XANES), extended X-ray absorption fine structure (EXAFS), X-ray magnetic circular dichroism (XMCD) and element-and site-specific magnetic hysteresis (ESMH) are used to elucidate the effect of geometry (0-3- and 2-2-type) on the magnetic properties of CoFe2O4-PbTiO3 (CFO-PTO) multiferroic composites by comparison with those of the reference CFO and PTO powders. Magnetic Co ions in CFO have been confirmed to be located at both the tetrahedral (A)- and octahedral (B)-sites. CFO retains its mixed-spinel structure as verified by the EXAFS, XMCD and ESMH measurements. ESMH measurements further demonstrate that the magnetic moments of Co2+ and Fe3+/Fe2+ cations at both the A-and B-sites in the composites are smaller than those of the CFO powder. The reduction of the magnetic moments in the 2-2-type composite was larger than that in the 0-3-type composite. The reduction of the magnetic moments in the composites was attributable to the formation of anti-phase boundaries owing to the compressive strain in CFO, which is the largest strain in the 2-2-type composite. Based on the Ti L-3,L-2-edge XMCD measurements of the CFO-PTO composites, no induced magnetic moment was observed at the Ti sites in the PTO matrix, excluding the possibility that the Ti ions in the PTO matrix affect the magnetic properties of these CFO-PTO composites.
Electrically controllable spontaneous magnetism in nanoscale mixed phase multiferroics
(2011-03-01)
He, Q.
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Chu, Y. -H.
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Heron, J. T.
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Yang, S. Y.
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Liang, W. I.
Magnetoelectrics and multiferroics present exciting opportunities for electric-field control of magnetism. However, there are few room-temperature ferromagnetic-ferroelectrics. Among the various types of multiferroics the bismuth ferrite system has received much attention primarily because both the ferroelectric and the antiferromagnetic orders are quite robust at room temperature. Here we demonstrate the emergence of an enhanced spontaneous magnetization in a strain-driven rhombohedral and super-tetragonal mixed phase of BiFeO(3). Using X-ray magnetic circular dichroism-based photoemission electron microscopy coupled with macroscopic magnetic measurements, we find that the spontaneous magnetization of the rhombohedral phase is significantly enhanced above the canted antiferromagnetic moment in the bulk phase, as a consequence of a piezomagnetic coupling to the adjacent tetragonal-like phase and the epitaxial constraint. Reversible electric-field control and manipulation of this magnetic moment at room temperature is also shown.
Electronic structure investigation of a charge density wave coupled to a metal-to-metal transition in Ce3Co4Sn13
(2018-12-18)
Singh, A.
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Huang, H. Y.
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Chin, Y. Y.
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Liao, Y. F.
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Huang, T. C.
We study the electronic structure of the skutterudite Ce3Co4Sn13, which is known to exhibit a charge density wave (CDW) transition, at temperature T-CDW similar to 160 K, coupled to a metal-to-metal transition. We use temperature dependent hard x-ray photoemission spectroscopy (HAXPES) and x-ray absorption spectroscopy (XAS) to investigate the occupied and unoccupied electronic states of Ce3Co4Sn13. The Co 2p and Sn 3p core level spectra show small but finite shifts in binding energy positions across T-CDW while Ce 3d core level spectra do not show any change across the transition. The Ce M-4,M-5-edge XAS spectrum compared with calculations indicate a typical trivalent ionic Ce3+ spectral shape, ruling out Kondo screening in Ce3Co4Sn13. In contrast, the Co L-2,L-3-edge XAS spectrum compared with a calculated spectrum shows evidence for hybridization with neighboring Sn atoms in a trigonal prismatic co-ordination. Temperature dependent XAS across the Co L-2,L-3-edge shows a small shift across T-CDW, consistent with HAXPES results. Detailed XAS measurements as a function of temperature show that the spectral shifts occur with a hysteresis across T-CDW , indicative of a first-order transition. Valence band spectra show a normal Fermi edge above and below T-CDW. The Co 3d states are observed at a binding energy of similar to 2 eV while the Ce 4f states occur as a weak feature within 0.5 eV of the Fermi level. The results suggest an unusual CDW transition coupled to a metal-to-metal transition in Ce3Co4Sn13.
Microscopic Origin of the Giant Ferroelectric Polarization in Tetragonal-like BiFeO(3)
(2011-09-29)
Zhang, J. X.
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He, Q.
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Trassin, M.
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Luo, W.
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Yi, D.
We report direct experimental evidence for a room-temperature, similar to 130 mu C/cm(2) ferroelectric polarization from the tetragonal-like BiFeO(3) phase. The physical origin of this remarkable enhancement of ferroelectric polarization has been investigated by a combination of x-ray absorption spectroscopy, scanning transmission electron microscopy, and first principles calculations. A large strain-induced Fe-ion displacement relative to the oxygen octahedra, combined with the contribution of Bi 6s lone pair electrons, is the mechanism driving the large ferroelectric polarization in this tetragonal-like phase.
Microscopic Origin of the Giant Ferroelectric Polarization in Tetragonal-like BiFeO3
(2011-09-29)
Zhang, J. X.
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He, Q.
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Trassin, M.
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Luo, W.
;
Yi, D.
We report direct experimental evidence for a room-temperature, similar to 130 mu C/cm(2) ferroelectric polarization from the tetragonal-like BiFeO3 phase. The physical origin of this remarkable enhancement of ferroelectric polarization has been investigated by a combination of x-ray absorption spectroscopy, scanning transmission electron microscopy, and first principles calculations. A large strain-induced Fe-ion displacement relative to the oxygen octahedra, combined with the contribution of Bi 6s lone pair electrons, is the mechanism driving the large ferroelectric polarization in this tetragonal-like phase.
Optical characterization of ZnMnO thin films on c-Al2O3
(2008-07-01)
Lin, H. J.
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Lin, D. Y.
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Wu, J. S.
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Chou, W. C.
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Yang, C. S.
Various optical measurement technologies have been used to characterize ZnMnO thin films with different Mn compositions grown by molecular beam epitaxy (MBE) on c-Al2O3 substrates. The lattice constant and the crystalization quality have been evaluated by using X-ray diffraction (XRD). Photoluminescence (PL) has been used to reveal the neutral-donor-bound exciton ((DX)-X-0) and to check the film's quality. Defect-related absorption signatures, in addition to near-band-edge absorption, due to the zinc vacancy and the donor-acceptor pair (DAP) have been found in the surface photovoltage spectra (SPS). Free excitonic transitions and their phonon-assisted replicas have been observed in the reflectance spectra. Our experimental results not only unveil specific optical transition energies but also indicate a rapid material deterioration when Mn incorporation goes beyond a certain amount to cause manganese segregation.
Orthorhombic BiFeO3
(2012-12-14)
Yang, J. C.
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He, Q.
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Suresha, S. J.
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Kuo, C. Y.
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Peng, C. Y.
A new orthorhombic phase of the multiferroic BiFeO3 has been created via strain engineering by growing it on a NdScO3(110)(o) substrate. The tensile-strained orthorhombic BiFeO3 phase is ferroelectric and antiferromagnetic at room temperature. A combination of nonlinear optical second harmonic generation and piezoresponse force microscopy revealed that the ferroelectric polarization in the orthorhombic phase is along the in-plane < 110 >(pc) directions. In addition, the corresponding rotation of the antiferromagnetic axis in this new phase was observed using x-ray linear dichroism. DOI: 10.1103/PhysRevLett.109.247606
The unconventional doping in YBa2Cu3O7-x/La0.7Ca0.3MnO3 heterostructures by termination control
(2017-01-16)
Tra, V. T.
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Huang, R.
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Gao, X.
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Chen, Y. -J.
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Liu, Y. T.
In strongly correlated oxides, heterostructures provide a powerful route to manipulate the charge, spin, orbital, and lattice degrees of freedom to create distinctive functionalities. In this work, we have achieved atomically precise interface control in YBa2Cu3O7-x/La0.7Ca0.3MnO3 (YBCO/LCMO) heterostructures and find a hidden effective doping. This mechanism is responsible for higher Tc in the sample with the MnO2-terminated interface than in that with the La0.7Ca0.3O-terminated interface. The MnO2-terminated sample also shows a larger magnetic moment of Mn together with a lower valence state. For more than a decade, the control of T-c in these heterostructures prior to this work has been solely via the variation of YBCO or LCMO thickness. This work hints at an alternative way of exploiting and exploring the interactions between superconductivity and magnetism in this system. Published by AIP Publishing.
Thermally or Magnetically Induced Polarization Reversal in the Multiferroic CoCr(2)O(4)
(2009-02-13)
Choi, Y. J.
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Okamoto, J.
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Huang, D. J.
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Chao, K. S.
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Lin, H. J.
We report the unexpected evolution, with thermal and magnetic-field (H) variations, of the interrelation between the polarization P, magnetization M, and spiral wave vector Q in CoCr(2)O(4), which has a ferrimagnetic conical-spiral magnetic order. For example, P suddenly jumps and changes its sign at the magnetic lock-in transition (T(L)) with thermal variation, or with isothermal variation of H (without changing its direction) at T(L), which surprisingly occurs without change in spiral handedness (i.e., the sign of Q). The presence of multiple spiral sublattices may be behind this unusual behavior.
Thermally or Magnetically Induced Polarization Reversal in the Multiferroic CoCr2O4
(2009-02-13)
Choi, Y. J.
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Okamoto, J.
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Huang, D. J.
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Chao, K. S.
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Lin, H. J.
We report the unexpected evolution, with thermal and magnetic-field (H) variations, of the interrelation between the polarization P, magnetization M, and spiral wave vector Q in CoCr2O4, which has a ferrimagnetic conical-spiral magnetic order. For example, P suddenly jumps and changes its sign at the magnetic lock-in transition (T-L) with thermal variation, or with isothermal variation of H (without changing its direction) at T-L, which surprisingly occurs without change in spiral handedness (i.e., the sign of Q). The presence of multiple spiral sublattices may be behind this unusual behavior.