Browsing by Author "Lin, C. M."

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Carrier gas effects on the SiGe quantum dots formation
(2008-07-30)
Lee, C. -H.
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Yu, C. -Y.
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Lin, C. M.
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Liu, C. W.
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Lin, H.
SiGe quantum dots (QDs) grown by ultra-high vacuum chemical vapor deposition using H(2) and He carrier gases are investigated and compared. SiGe QDs using He carrier gas have smaller dot size with a better uniformity in terms of dot height and dot base as compared to the H(2) carrier gas. There is a higher Ge composition and less compressive strain in the SiGe QDs grown in He than in H(2) as measured by Raman spectroscopy. The Ge content is higher for He growth than H(2) growth due to hydrogen induced Si segregation and the lower interdiffusivity caused by the more strain relaxation in the He-grown SiGe dots. The photoluminescence also confirms more compressive strain for H(2) growth than He growth. Hydrogen passivation and Ge-H cluster formation play an important role in the QDs growth. (C) 2008 Elsevier B. V. All rights reserved.
Device Instability of ReRAM and a Novel Reference Cell Design for Wide Temperature Range Operation
(2017-09-01)
Lin, Y. H.
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Lin, Y. Y.
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Lee, F. M.
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Ho, Y. H.
;
Hsu, K. C.
This letter addresses two difficult challenges for transition metal oxide resistive random access memories (ReRAMs)-sensitivity to operation temperature and random fluctuation of resistance value. A careful study of a WOx ReRAM array reveals that these devices are unstable and their read currents fluctuate with time due to random telegraph noise and structure relaxation. Consequently, even after careful programming, the current distribution can broaden with time and tail bit population grows. Furthermore, ReRAM state is sensitive to temperature and a reference cell made of the same device material must be used. Thus, although the broadening of read current distribution may be tolerated by creating a larger RESET/SET memory window, the current fluctuation still makes it impossible to predict the output of the reference cell, leading to array malfunction. This letter investigates the current (resistance) instability in detail and proposes a reference array with a novel trimming method that can stabilize the reference current level. The proposed reference array has very good dc stress reliability as well as wide-range temperature tracking performance from -40 degrees C to 85 degrees C.
Modifications of MnO6 Octahedra in DyMnO3 under High Pressure
(2010-01-01)
Chou, T. L.
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Lee, J. M.
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Chen, S. A.
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Ishii, H.
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Hiraoka, N.
Local geometry and electronic states of octahedrally coordinated Mn ions in orthorhombic DyMnO3 have been studied by partial-fluorescence-yield spin-selective x-ray absorption spectroscopy and in-situ Raman scattering. As evidenced in absorption near-edge structure and Raman spectra, the external pressure alleviates the MnO6 octahedral distortion and Jahn-Teller effect with enhanced octahedral tilt.
Pressure-dependent electronic structures in multiferroic DyMnO(3): A combined lifetime-broadening-suppressed x-ray absorption spectroscopy and ab initio electronic structure study
(2010-10-21)
Chen, J. M.
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Lee, J. M.
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Chou, T. L.
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Chen, S. A.
;
Huang, S. W.
Variations in the electronic structure and structural distortion in multiferroic DyMnO(3) were probed by synchrotron x-ray diffraction, lifetime-broadening-suppressed x-ray absorption spectroscopy (XAS), and ab initio electronic structure calculations. The refined x-ray diffraction data enabled an observation of a diminished local Jahn-Teller distortion of Mn sites within MnO(6) octahedra in DyMnO(3) on applying the hydrostatic pressure. The intensity of the white line in Mn K-edge x-ray absorption spectra of DyMnO(3) progressively increased with the increasing pressure. With the increasing hydrostatic pressure, the absorption threshold of an Mn K-edge spectra of DyMnO(3) shifted toward a greater energy, whereas the pre-edge line slightly shifted to a smaller energy. We provide the spectral evidence for the pressure-induced bandwidth broadening for manganites. The intensity enhancement of the white line in Mn K-edge spectra is attributed to a diminished Jahn-Teller distortion of MnO(6) octahedra in compressed DyMnO(3). A comparison of the pressure-dependent XAS spectra with the ab initio electronic structure calculations and full calculations of multiple scattering using the code FDMNES shows the satisfactory agreement between experimental and calculated Mn K-edge spectra. (C) 2010 American Institute of Physics. [doi:10.1063/1.3490400]
Pressure-dependent electronic structures in multiferroic DyMnO3: A combined lifetime-broadening-suppressed x-ray absorption spectroscopy and ab initio electronic structure study
(2010-10-21)
Chen, J. M.
;
Lee, J. M.
;
Chou, T. L.
;
Chen, S. A.
;
Huang, S. W.
Variations in the electronic structure and structural distortion in multiferroic DyMnO3 were probed by synchrotron x-ray diffraction, lifetime-broadening-suppressed x-ray absorption spectroscopy (XAS), and ab initio electronic structure calculations. The refined x-ray diffraction data enabled an observation of a diminished local Jahn-Teller distortion of Mn sites within MnO6 octahedra in DyMnO3 on applying the hydrostatic pressure. The intensity of the white line in Mn K-edge x-ray absorption spectra of DyMnO3 progressively increased with the increasing pressure. With the increasing hydrostatic pressure, the absorption threshold of an Mn K-edge spectra of DyMnO3 shifted toward a greater energy, whereas the pre-edge line slightly shifted to a smaller energy. We provide the spectral evidence for the pressure-induced bandwidth broadening for manganites. The intensity enhancement of the white line in Mn K-edge spectra is attributed to a diminished Jahn-Teller distortion of MnO6 octahedra in compressed DyMnO3. A comparison of the pressure-dependent XAS spectra with the ab initio electronic structure calculations and full calculations of multiple scattering using the code FDMNES shows the satisfactory agreement between experimental and calculated Mn K-edge spectra. (C) 2010 American Institute of Physics. [doi:10.1063/1.3490400]
Pressure-induced structural distortion of TbMnO(3): A combined x-ray diffraction and x-ray absorption spectroscopy study
(2009-04-01)
Chen, J. M.
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Chou, T. L.
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Lee, J. M.
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Chen, S. A.
;
Chan, T. S.
The variation of electronic states and structural distortion in highly compressed multiferroic TbMnO(3) was probed by x-ray diffraction (XRD) and x-ray absorption spectroscopy (XAS) using synchrotron radiation. Refined XRD data enabled observation of a reduced local Jahn-Teller (JT) distortion of Mn sites within MnO(6) octahedra in TbMnO(3) with increasing hydrostatic pressure. A progressively increasing intensity of the white line in Mn K-edge x-ray absorption spectra of TbMnO(3) was detected with increasing pressure. The absorption threshold of Mn K-edge spectra of TbMnO(3) is shifted toward higher energy, whereas the pre-edge peak is slightly shifted to lower energy with increasing hydrostatic pressure. We provide spectral evidence for pressure-induced bandwidth broadening for mangnites. The enhanced intensity of the white line and the shifted absorption threshold of Mn K-edge spectra are explained in terms of a reduced JT distortion of MnO(6) octahedra in compressed TbMnO(3). Comparison of XAS data with full-multiple-scattering calculations using code FDMNES shows satisfactory agreement between experimental and calculated Mn K-edge spectra.
Pressure-induced structural distortion of TbMnO3: A combined x-ray diffraction and x-ray absorption spectroscopy study
(2009-04-01)
Chen, J. M.
;
Chou, T. L.
;
Lee, J. M.
;
Chen, S. A.
;
Chan, T. S.
The variation of electronic states and structural distortion in highly compressed multiferroic TbMnO3 was probed by x-ray diffraction (XRD) and x-ray absorption spectroscopy (XAS) using synchrotron radiation. Refined XRD data enabled observation of a reduced local Jahn-Teller (JT) distortion of Mn sites within MnO6 octahedra in TbMnO3 with increasing hydrostatic pressure. A progressively increasing intensity of the white line in Mn K-edge x-ray absorption spectra of TbMnO3 was detected with increasing pressure. The absorption threshold of Mn K-edge spectra of TbMnO3 is shifted toward higher energy, whereas the pre-edge peak is slightly shifted to lower energy with increasing hydrostatic pressure. We provide spectral evidence for pressure-induced bandwidth broadening for mangnites. The enhanced intensity of the white line and the shifted absorption threshold of Mn K-edge spectra are explained in terms of a reduced JT distortion of MnO6 octahedra in compressed TbMnO3. Comparison of XAS data with full-multiple-scattering calculations using code FDMNES shows satisfactory agreement between experimental and calculated Mn K-edge spectra.
Studies on the electronic and vibrational states of colloidal CdSe/ZnS quantum dots under high pressures
(2007-05-09)
Yuan, C. T.
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Lin, Y. C.
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Chen, Y. N.
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Chiu, Q. L.
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Chou, W. C.
The electronic and vibrational states of colloidal core/shell CdSe/ZnS quantum dots are studied at room temperature by using high pressure optical measurements. Pressure-induced quadratic variations of lattice constants can be observed clearly from both photoluminescence ( PL) and Raman spectra up to similar to 7 GPa. This quadratic relationship is consistent with the theoretical prediction. The pressure coefficients of linear and quadratic terms are 32 meV GPa(-1), -1 meV GPa(-2) for PL and 4.2 cm(-1) GPa(-1), -0.1 cm(-1) GPa(-2) for Raman measurements, respectively.