Browsing by Author "Liang, K. S."

Now showing 1 - 10 of 10

An Algorithm for the Optimization of Insertion Devices to Increase Useful Flux and to Decrease Useless Radiation Power
(2010)
Chen, S. D.
;
Hwang, C. S.
;
Liang, K. S.
;
電子物理學系
;
Department of Electrophysics
A continuous spectrum of synchrotron radiation in the hard x-ray region, 5-20 keV, is necessary for the special demand of users, but the high radiation power in that continuous spectrum adversely affects the design of optical components in the beam line. A compromise between photon flux and radiation power of insertion devices should hence be considered. An algorithm and code for spectrum optimization was hence developed using program Mathematica. A wiggler-like undulator with a continuous spectrum was investigated with this code. An optimization algorithm for continuous spectra in the energy range 5-20 keV is presented, and features of the wiggler-like undulator with a continuous spectrum are discussed herein.
Bonding anisotropy in multiferroic TbMnO(3) probed by polarization dependent x-ray absorption spectroscopy
(2009-01-26)
Chen, J. M.
;
Lee, J. M.
;
Chen, C. K.
;
Chou, T. L.
;
Lu, K. T.
O K- and Mn L(2,3)-edges x-ray absorption spectra of orthorhombic TbMnO(3) single crystals show strong polarization dependence, in contrast with results of previous experiments on orthorhombic LaMnO(3) and DyMnO(3) thin films that show nearly isotropic spectral structure. First-principles calculations reveal that TbMnO(3) exhibits a zigzag e(g) orbital ordering ground state. The highly distorted MnO(6) octahedron and orbital ordering in TbMnO(3) produce highly anisotropic Mn-O bonding within the ab plane, a frustration of the magnetic ordering, and the formation of complicated incommensurate magnetic structures.
Bonding anisotropy in multiferroic TbMnO3 probed by polarization dependent x-ray absorption spectroscopy
(2009-01-26)
Chen, J. M.
;
Lee, J. M.
;
Chen, C. K.
;
Chou, T. L.
;
Lu, K. T.
O K- and Mn L-2,L-3-edges x-ray absorption spectra of orthorhombic TbMnO3 single crystals show strong polarization dependence, in contrast with results of previous experiments on orthorhombic LaMnO3 and DyMnO3 thin films that show nearly isotropic spectral structure. First-principles calculations reveal that TbMnO3 exhibits a zigzag e(g) orbital ordering ground state. The highly distorted MnO6 octahedron and orbital ordering in TbMnO3 produce highly anisotropic Mn-O bonding within the ab plane, a frustration of the magnetic ordering, and the formation of complicated incommensurate magnetic structures.
CARBON-DOPED TiO2 NANOTUBES: EXPERIMENTAL AND COMPUTATIONAL STUDIES
(2013-05-01)
Huang, Wen-Fei
;
Wu, Pin-Jiun
;
Hsu, Wei-Chih
;
Wu, Chih-Wei
;
Liang, K. S.
C-doped TiO2 nanotubes (NTs) with anatase structure, prepared by anodizing the polished Ti foils, were characterized using X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), and synchrotron-based X-ray photoemission spectroscopy (XPS). XPS results show electron losses in C atoms, no electron change in Ti atoms, and two doping energy levels appeared in band gaps. Structural geometries, DOSs, PDOSs, and Bader charge analyses of C-doped TiO2 anatase are predicted by periodic DFT calculations. Eight doping positions were taken into consideration: two substitutional cases (in oxygen and titanium sites) and six interstitial cases. We found that the interstitial carbon doping type is the most stable one, whereas the substitutional cases are rather unstable. Band-gap modifications can also be found in oxygen substitution, but not in titanium substitution. Both band-gap modification and non-band-gap modification are found in the interstitial carbon doping. In these eight C-doping systems, only the C atom in the oxygen substitution case gains electrons, 1.14 e, and others present electron losses within 0.5-4.00 e. The results of XPS measurements, DOSs calculations, and Bader charge analyses show that carbon interstitial is the most likely doping type for the C-doped TiO2 NTs.
Dark field image of full-field transmission hard x-ray microscope in 8-11 keV
(2006-01-01)
Yin, Gung-Chian
;
Duewer, Fred
;
Zeng, Xianghui
;
Lyon, Alan
;
Yun, Wenbing
We have demonstrated dark-field imaging using a full-field hard x-ray microscope by using a custom capillary-based condenser. The condenser provides illumination with a numeric aperture about 3-mrad with high efficiency. This high illumination angle allows full-resolution imaging using a 50 rim hard x-ray zone plate. The zeroth order beam from the condenser is well out of the zoneplate range - which allows a high signal-to-noise ratio in the image plane. Small particles with high scattering power, such as colloidal gold markers used in biology are well-suited for dark-field imaging. Combining with high brightness source from NSRRC BL01B, the dark field image can be acquired within several minutes with high contrast ratio. In this paper, the dark field image of IC and the zoneplate defect will be demonstrated and studied in different energy under dark field mode.
Development of a superconducting elliptically polarized undulator
(2010)
Chen, S. D.
;
Jan, J. C.
;
Hwang, C. S.
;
Liang, K. S.
;
電子物理學系
A superconducting, elliptically polarized undulator (SEPU24) with a period of length 24 mm was developed to provide first-harmonic photons from a 0.8 GeV storage ring for extreme-ultraviolet (EUV) lithography experiment. In SEPU24, two layers of a magnet array structure - with and without rotated magnet arrays - are combined to generate a helical field that provides radiation with wavelength 13.5 nm in the in-band energy. The arrays of iron and aluminium poles were wound with a racetrack coil vertically as for the magnet pole array. The elliptical field is created when the up and down magnet-pole arrays pass excitation currents in alternate directions. SEPU24 is designed with a magnet of gap 6.8 mm, yielding magnetic flux density B-x=B-z=0.61 T of the helical field. A prototype magnet was fabricated with a diode for quench protection, and assembled in a test dewar to test the magnet performance. A cryogenic Hall-probe system with a precise linear stage was used to measure the distribution of the magnetic field. We describe the design concept and algorithm, the engineering design, the calculation of the magnetic field, the construction and testing of the 10-pole prototype magnet and related issues.
Imaging cells and sub-cellular structures with ultrahigh resolution full-field X-ray microscopy
(2013-05-01)
Chien, C. C.
;
Tseng, P. Y.
;
Chen, H. H.
;
Hua, T. E.
;
Chen, S. T.
Our experimental results demonstrate that full-field hard-X-ray microscopy is finally able to investigate the internal structure of cells in tissues. This result was made possible by three main factors: the use of a coherent (synchrotron) source of X-rays, the exploitation of contrast mechanisms based on the real part of the refractive index and the magnification provided by high-resolution Fresnel zone-plate objectives. We specifically obtained high-quality microradiographs of human and mouse cells with 29 nm Rayleigh spatial resolution and verified that tomographic reconstruction could be implemented with a final resolution level suitable for subcellular features. We also demonstrated that a phase retrieval method based on a wave propagation algorithm could yield good subcellular images starting from a series of defocused microradiographs. The concluding discussion compares cellular and subcellular hard-X-ray microradiology with other techniques and evaluates its potential impact on biomedical research. (C) 2012 Elsevier Inc. All rights reserved.
Influence of the threading dislocations on the electrical properties in epitaxial ZnO thin films
(2006-12-29)
Liu, W. -R.
;
Hsieh, W. F.
;
Hsu, C. -H.
;
Liang, K. S.
;
Chien, F. S. -S.
The structural and electrical properties of epitaxial ZnO films grown by pulsed-laser deposition on sapphire (0001) were investigated by high-resolution X-ray diffraction (XRD), atomic force microscopy (AFM), scanning capacitance microscopy (SCM), conductive atomic force microscopy (C-AFM), and transmission electron microscopy (TEM). The results of XRD and AFM revealed that the ZnO films have a columnar-grain structure consisting of epitaxial cores surrounded by annular boundaries. The core and boundary regions exhibited significantly different capacitive responses and field emission current. The results of TEM indicated that the annular boundaries have high-density edge threading dislocations. The shift of flatband voltage and the raise of potential barrier at the boundaries observed by SCM and C-AFM were attributed to the interface trap densities caused by the existence of high-density edge threading dislocations. (c) 2006 Elsevier B.V. All rights reserved.
Resonant x-ray emission spectroscopy of multiferroic TbMnO3
(2007-07-30)
Chen, J. M.
;
Chen, C. K.
;
Chou, T. L.
;
Jarrige, I.
;
Ishii, H.
The Mn 3d valence states in single-crystalline TbMnO3 were probed using x-ray absorption spectroscopy and resonant x-ray emission spectroscopy (RXES). The polarized Mn K-edge x-ray absorption spectra show a strong polarization dependence, particularly for the white line region, indicating the strong anisotropic Mn-O bonding within the ab plane in TbMnO3. The RXES data obtained at the Mn K edge clearly reveal that unoccupied Mn 3d states exhibit a relatively delocalized character, stemming from hybridization of the Mn 3d states with the neighboring Mn 4p orbitals. The authors demonstrated that resonant x-ray emission spectroscopy is able to characterize the degree of localization of the unoccupied states or hole carriers in manganites.
Very small photoluminescent gold nanoparticles for multimodality biomedical imaging
(2013-05-01)
Lai, Sheng-Feng
;
Chien, Chia-Chi
;
Chen, Wen-Chang
;
Chen, Hsiang-Hsin
;
Chen, Yi-Yun
An original synthesis method based on X-ray irradiation produced gold nanoparticles (AuNPs) with two important properties for biomedical research: intense visible photoluminescence and very high accumulation in cancer cells. The nanoparticles, coated with MUA (11-mercaptoundecanoid acid), are very small (1.4 nm diameter); the above two properties are not present for even slightly larger sizes. The small MUA-AuNPs are non-cytotoxic (except for very high concentrations) and do not interfere with cancer cell proliferation. Multimodality imaging using visible light fluorescence and X-ray microscopy is demonstrated by tracing the nanoparticle-loaded tumor cells. (C) 2012 Elsevier Inc. All rights reserved.