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Featured researches published by Hsian-Hong Chang.


Publications of the Astronomical Society of Japan | 2016

First-generation science cases for ground-based terahertz telescopes

Hiroyuki Hirashita; Patrick M. Koch; Satoki Matsushita; Shigehisa Takakuwa; Masanori Nakamura; Keiichi Asada; Hauyu Baobab Liu; Yuji Urata; Ming-Jye Wang; Wei-Hao Wang; Satoko Takahashi; Ya-Wen Tang; Hsian-Hong Chang; Kuiyun Huang; Oscar Morata; Masaaki Otsuka; Kai-Yang Lin; An-Li Tsai; Yen-Ting Lin; S. Srinivasan; Pierre Martin-Cocher; Hung-Yi Pu; F. Kemper; Nimesh A. Patel; Paul K. Grimes; Yau-De Huang; Chih-Chiang Han; Yen-Ru Huang; Hiroaki Nishioka; Lupin Chun-Che Lin

Ground-based observations at terahertz (THz) frequencies are a newly explorable area of astronomy for the next ten years. We discuss science cases for a first-generation 10-m class THz telescope, focusing on the Greenland Telescope as an example of such a facility. We propose science cases and provide quantitative estimates for each case. The largest advantage of ground-based THz telescopes is their higher angular resolution (~ 4 arcsec for a 10-m dish), as compared to space or airborne THz telescopes. Thus, high-resolution mapping is an important scientific argument. In particular, we can isolate zones of interest for Galactic and extragalactic star-forming regions. The THz windows are suitable for observations of high-excitation CO lines and [N II] 205 um lines, which are scientifically relevant tracers of star formation and stellar feedback. Those lines are the brightest lines in the THz windows, so that they are suitable for the initiation of ground-based THz observations. THz polarization of star-forming regions can also be explored since it traces the dust population contributing to the THz spectral peak. For survey-type observations, we focus on ``sub-THz extragalactic surveys, whose uniqueness is to detect galaxies at redshifts z ~ 1--2, where the dust emission per comoving volume is the largest in the history of the Universe. Finally we explore possibilities of flexible time scheduling, which enables us to monitor active galactic nuclei, and to target gamma-ray burst afterglows. For these objects, THz and submillimeter wavelength ranges have not yet been explored.


Journal of Applied Physics | 2006

Magnetic properties of ultrathin Co/Ge (111) film with oxygen surfactant

Hsian-Hong Chang; Jyh Shen Tsay; Y.L. Chiou; K.T. Huang; W. Y. Chan; Y. D. Yao

Magnetic properties of ultrathin Co∕Ge(111) films with oxygen surfactant have been investigated using surface magneto-optic Kerr effect technique. As the oxygen exposure increases, their magnetic properties could be significantly modified. As the thickness of Co films increases to above 6 ML (monolayer), pure cobalt islands start to accumulate on the surface and the amount of oxygen on the surface layers increases with increasing oxygen exposure time. Series experiments of different sequences of oxygen exposure and Co deposition have been performed. From the results of slight chemical shift and depth profiling measurements, one can conclude that oxygen plays a role as a surfactant. The adsorbed oxygen influences the electronic density of states of Co and leads to the changes of the magnetic properties. The appearance of the O∕Co∕Ge interface could modify the stress anisotropy, and as a result the coercivity of 30 ML Co∕Ge(111) increases from 730to810Oe with 500L of oxygen exposure.


Applied Physics Letters | 2014

Graphene-based terahertz photodetector by noise thermometry technique

Ming-Jye Wang; Ji-wun Wang; Chun-Lun Wang; Yen-Yu Chiang; Hsian-Hong Chang

We report the characteristics of graphene-based terahertz (THz) photodetector based on noise thermometry technique by measuring its noise power at frequency from 4 to 6 GHz. Hot electron system in graphene microbridge is generated after THz photon pumping and creates extra noise power. The equivalent noise temperature and electron temperature increase rapidly in low THz pumping regime and saturate gradually in high THz power regime which is attributed to a faster energy relaxation process involved by stronger electron-phonon interaction. Based on this detector, a conversion efficiency around 0.15 from THz power to noise power in 4–6u2009GHz span has been achieved.


Journal of Applied Physics | 2006

Step edge growth of Co nanoislands on Cu(111) surface

Hsian-Hong Chang; F.T. Yuan; Y. D. Yao; W. Y. Cheng; Wei-Bin Su; Chia-Seng Chang; C. W. Lee; Wei-Chun Cheng

Step edge growth of Co nanoislands on Cu(111) surface have been investigated by scanning tunneling microscopy (STM). The cobalt atoms cluster at the upper step edges and form bilayer islands of 2nm in diameter (about nine Co atoms in width) initially during the initial stage of Co deposition. This result is in accordance with the total energy calculations within density functional theory. Besides, the size and amount of nanoislands increase with increasing coverage. The average number of Co atoms contained in one island increases with a rate of 375 atoms per monolayer (ML). The statistics data on the STM images indicate that the cobalt nanoislands preferentially grow at the upper step edge during the first stage of Co deposition, then toward terrace, and finally, the growth rate of islands in edge is almost the same as that in terrace for Co thickness above 0.78–1.42 ML.


Journal of Applied Physics | 2011

Elastic stiffness of single-crystalline FeSe measured by picosecond ultrasonics

Yu-Chieh Wen; Y. C. Liao; Hsian-Hong Chang; B. H. Mok; Y. J. Lee; Tzu-Wen Huang; Kuo-Wei Yeh; J. Y. Luo; Ming-Jye Wang; Chi-Kuang Sun; M. K. Wu

We report investigations on the elasticity of superconducting FeSe using picosecond ultrasonic technique. The tetragonal (001) FeSe thin film, deposited on a processed SrTiO3 substrate by the pulsed laser deposition, exhibits distinct c-axis preferred orientation and single-crystalline features as a result of the x-ray diffraction. The high-quality crystallinity thus enables quantitative examinations of anisotropic stiffness coefficients (C33) of FeSe, correlating to the interatomic interaction in the simplest iron-based superconductor. Our experiment indicates a room-temperature C33 of 40.9u2009±u20090.4u2009GPa and material stiffening of 4.3% at low temperatures, which can be explained by the weakening of anharmonic phonon–phonon interactions.


IEEE Transactions on Applied Superconductivity | 2011

Noise and Bandwidth of 0.5-THz Twin Vertically Stacked SIS Junctions

Jing Li; Sheng-Cai Shi; Dong Liu; Kang-Ming Zhou; Ming-Jye Wang; Tse-Jun Chen; C. Chen; Wei-Chun Lu; Chuang-Ping Chiu; Hsian-Hong Chang

Twin SIS (superconductor-insulator-superconductor) junctions, with a simple structure, yet large bandwidth and low noise temperature, have been widely used in millimeter- and submillimeter-wave heterodyne mixers. With increasing frequency, however, the length of the tuning inductance connecting the two individual SIS junctions becomes short while the junction area remains fixed. With a relatively short tuning inductance, the effect of the junctions spreading inductance becomes non-negligible, and device fabrication becomes more difficult. By adopting vertically stacked SIS junctions (VSJs), which have an equivalent geometric capacitance inversely proportional to the junction number, it becomes feasible to increase the junction tuning inductance. In this paper, we report on the design, fabrication, and characterization of twin Nb/Al-AlOx/Nb/Al-AlOx/Nb VSJs for the 500-GHz frequency band.


ursi asia pacific radio science conference | 2016

Development of 1.5 THz cartridge-type multi-pixel receiver based on HEB mixers

Yen-Ru Huang; Chuang-Ping Chiu; Wei-Chun Lu; Hsian-Hong Chang; Yen-Yu Chiang; Ming-Jye Wang

A novel design of 2 × 2 NbN hot electron bolometer (HEB) mixer array receiver has been demonstrated here by using the multiple local oscillator (LO) beams obtained from a power distributor. In our design, the 1.5 THz LO beam is split into four uniform sub-beams with a spacing of 18 mm, then arrives at a four-pixel silicon lens with twin slot antenna (TSA) through a large-area beam splitter. An additional four-pixel HDPE lens is located at 120 mm in front of the silicon lens to increase the size of beam waist for fitting to the aperture parameter of sub-reflector. This design can match the optical parameters between Si/TSA and GLT antenna. The pixel number can be further extended to 9 based on the available LO power.


Materials Research Express | 2014

Structural characteristics and phase separation of superconducting Fe1+ySe1−xTex nanowires

Ta-Kun Chen; Chung-Chieh Chang; H.Y. Tang; Hsian-Hong Chang; Yu-Ruei Wu; Min-Hsueh Wen; Y. J. Lee; Ming-Jye Wang; M. K. Wu; Fu-Rong Chen; Dirk Van Dyck

Superconducting Fe1+y Se1?x Te x nanowires with considerable differences in the diameter and aspect ratio were synthesized via annealing thin films with particular composition prepared by pulsed laser deposition. Using transmission electron microscopy and related techniques, we found they were all crystallized in a PbO-type tetragonal structure with a growth direction of [010] (equivalent to [100]). All the nanowires were covered by a thin amorphous oxide layer (?5 nm) determined by electron energy loss spectroscopy. Chemical analysis and the calculated lattice constants reveal the fact that these nanowires are different from chemical compositions. High-resolution electron microscopy images show that the two thick nanowires (with diameters ?80 nm) are composed of multiple phases, while the thin nanowires (with diameters of 14 and 22 nm) are single phase. Digital moir? analysis reveals that the thin nanowires contain surface defects, as well as dislocations, inside the nanowires.


Proceedings of the National Academy of Sciences of the United States of America | 2014

Fe-vacancy order and superconductivity in tetragonal β-Fe1-xSe

Ta-Kun Chen; Chung-Chieh Chang; Hsian-Hong Chang; Ai-Hua Fang; Chih-Han Wang; Wei-Hsiang Chao; Chuan-Ming Tseng; Y. J. Lee; Yu-Ruei Wu; Min-Hsueh Wen; H.Y. Tang; Fu-Rong Chen; Ming-Jye Wang; M. K. Wu; Dirk Van Dyck


Journal of Magnetism and Magnetic Materials | 2006

Comparison on the phase evolution and magnetic properties of direct-quenched Pr8.5Fe79.5M2B10 (M=Cr, Nb, Ti, V, and Zr) ribbons

Hsian-Hong Chang; C.H. Chiu; C.W. Chang; C.H. Chen; W.C. Chang; A.C. Sun; Y. D. Yao

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Y. D. Yao

Fu Jen Catholic University

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Y. J. Lee

National Tsing Hua University

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Fu-Rong Chen

National Tsing Hua University

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H.Y. Tang

National Tsing Hua University

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