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Characterization of (Mn, Co)-Codoped ZnO Nanorods Prepared by Thermal Diffusion
The-Long Phan,Vincent, R.,Cherns, D.,Nguyen Huy Dan,Seong-Cho Yu IEEE 2009 IEEE transactions on magnetics Vol.45 No.6
<P>We prepared (Mn, Co)-codoped ZnO nanorods by thermal diffusion using pure ZnO nanorods, Mn and Co fragments as precursors. Detailed investigations of X-ray diffraction, electron microscopy, photoluminescence and Raman scattering spectroscopy revealed the incorporation of dopants Mn and Co into the ZnO host lattice. This did not change much the lattice parameters of ZnO, and not lead to the development of secondary phases related to the dopants. Compared with magnetic behaviors of two reference samples of Mn- and Co-doped ZnO nanorods, we observed the decrease of magnetic ordering in (Mn, Co)-codoped ZnO nanorods. This could be explained that magnetic interaction between Mn and Co ions is antiferromagnetic.</P>
Diffusion of Mn in ZnO nanowires annealed in air.
Phan, T L,Sun, Y K,Vincent, R,Cherns, D,Yu, S C American Scientific Publishers 2009 Journal of Nanoscience and Nanotechnology Vol.9 No.2
<P>We studied diffusion of Mn in ZnO nanowires by means of field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, photoluminescence and Raman scattering spectroscopy. The Mn-diffused samples were prepared by covering synthesized ZnO nanowires with a Mn chip and then annealing at temperatures between 200 and 1000 degrees C for 1 h in air. Microstructural analyses, and photoluminescence and Raman studies revealed that Mn atoms started diffusing in ZnO nanowires at 800 degrees C. The annealing-temperature increase up to 1000 degrees C led to a strong diffusion of Mn in the ZnO host lattice, which caused the blueshift of the ultra-violet emission. Concurrently, recored Raman scattering spectra showed some additional Mn-related modes. The origin of these lines was discussed in detail.</P>
Optical Prperties of Mn-Doped ZnO Nanowires
판더롱,Yue-Kui Sun,Roger Vincent,유성초,David Cherns,Nguyen Xuan Nghia 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.5
We used chemical vapor deposition to prepare ZnO nanowires. After that, the synthesized nanowires were doped with Mn by using thermal diffusion. The optical properties of the samples were investigated by means of using photoluminescence (PL) and Raman scattering (RS) spec- troscopy. The presence of Mn in the ZnO nanowires changed in the RS intensity at wavenumbers between 500 and 600 cm..1 and resulted in generation of longitudinal optical (LO) phonons at higher orders. The recorded PL spectra revealed the dependences of the PL intensity and the emission peak position on the Mn doping. Our results also indicated that the incorporation of a small amount of Mn into ZnO nanowires did not modify the wurtzite structure, but improved signifiantly the luminescence effciency of the ZnO nanowires.
Chern, Li Ern,Hwang, Kyusung,Mizoguchi, Tomonari,Huh, Yejin,Kim, Yong Baek American Physical Society 2017 Physical Review B Vol.96 No.3
<P>The Kagome-lattice-based material, volborthite, Cu3V2O7(OH)(2) center dot 2H(2)O, has been considered as a promising platform for discovery of unusual quantum ground states due to the frustrated nature of spin interaction. We explore possible quantum spin liquid and magnetically ordered phases in a two-dimensional nonsymmorphic lattice, which is described by the plane group p2gg, consistent with the spatial anisotropy of the spin model derived from density functional theory (DFT) for volborthite. Using the projective symmetry group (PSG) analysis and Schwinger boson mean field theory, we classify possible spin liquid phases with bosonic spinons and investigate magnetically ordered phases connected to such states. It is shown, in general, that only translationally invariant mean field spin liquid ansatzes are allowed in two-dimensional nonsymmorphic lattices. We study the mean field phase diagram of the DFT-derived spin model and find that possible quantum spin liquid phases are connected to two types of magnetically ordered phases, a coplanar incommensurate (q, 0) spiral order as the ground state and a closely competing coplanar commensurate (pi, pi) spin density wave order. In addition, periodicity enhancement of the two-spinon continuum, a consequence of symmetry fractionalization, is found in the spin liquid state connected to the (pi, pi) spin density wave order. We discuss relevance of these results to recent and future experiments on volborthite.</P>
ON THE UNIQUENESS FOR ENTIRE FUNCTIONS
Chern, Peter Tien-Yu,Kim, Jong-Jin,Kim, In-Su The Honam Mathematical Society 2007 호남수학학술지 Vol.29 No.4
We establish two uniqueness theorems for non-constant entire functions which extends results of J. S. Hwang in J. Math. Anal. and its Appl. Vol. 37 (1972) 452-456.
Chern-Hwa Chen,Cheng-Hsin Chang,Yuh-Yi Lin 한국풍공학회 2013 Wind and Structures, An International Journal (WAS Vol.16 No.2
A wind tunnel test of a scaled-down model and field measurement were effective methods for elucidating the aerodynamic behavior of a chimney under a wind load. Therefore, the relationship between the results of the wind tunnel test and the field measurement had to be determined. Accordingly, the set-up and testing method in the wind tunnel had to be modified from the field measurement to simulate the real behavior of a chimney under the wind flow with a larger Reynolds number. It enabled the results of the wind tunnel tests to be correlated with the field measurement. The model surface roughness and different turbulence intensity flows were added to the test. The simulated results of the wind tunnel test agreed with the full-scale measurements in the mean surface pressure distribution behavior.
ON THE ENTIRE SERIES WITH FINITE LOGARITHMIC ORDER
Chern, Peter Tien-Yu,Kim, In-Soo The Honam Mathematical Society 2011 호남수학학술지 Vol.33 No.3
We deal with a kind of impossible decomposition of some entire functions in terms of a certain form.
THE ASYMPTOTIC STABILITY OF SOME INTEGRODIFFERENTIAL EQUATIONS
Chern, Jann-Long,Huang, Shu-Zhu Korean Mathematical Society 2000 대한수학회보 Vol.37 No.2
In this paper we consider two delay equations with in-finite delay. We will give two sufficient conditions for the positive and zero equilibriums of these equations to be a global attractor respectively.
Fermionic spin liquid analysis of the paramagnetic state in volborthite
Chern, Li Ern,Schaffer, Robert,Sorn, Sopheak,Kim, Yong Baek American Physical Society 2017 Physical Review B Vol.96 No.16
<P>Recently, thermal Hall effect has been observed in the paramagnetic state of volborthite, which consists of distorted kagome layers with S = 1/2 local moments. Despite the appearance of magnetic order below 1 K, the response to external magnetic field and unusual properties of the paramagnetic state above 1 K suggest possible realization of exotic quantum phases. Motivated by these discoveries, we investigate possible spin liquid phases with fermionic spinon excitations in a nonsymmorphic version of the kagome lattice, which belongs to the two-dimensional crystallographic group p2gg. This nonsymmorphic structure is consistent with the spin model obtained in the density functional theory calculation. Using projective symmetry group analysis and fermionic parton mean field theory, we identify twelve distinct Z(2) spin liquid states, four of which are found to have correspondence in the eight Schwinger boson spin liquid states we classified earlier. We focus on the four fermionic states with bosonic counterpart and find that the spectrum of their corresponding root U(1) states features spinon Fermi surface. The existence of spinon Fermi surface in candidate spin liquid states may offer a possible explanation of the finite thermal Hall conductivity observed in volborthite.</P>
Chern-Sheng Lin,Jen Min Tsai,Kai-Sheng Chen,Yun-Long Lay,Nin-Chun Chang 한국정밀공학회 2014 International Journal of Precision Engineering and Vol. No.
In this paper an automatic optical inspection system for the advanced fiber coupler assembly manufacturing process is presented. Coupling efficiency variations were compared with axial displacement. The main standard components of light peak fiber couplerswere used in the experiment to determine the corresponding offset and position of the optimal optical coupling efficiency in order toachieve a positioning effect. This study used the parameters of lens curvature, focal length and light source for validation using opticaldesign software. An infrared CCD camera was used to extract the coupled light spot images. The curve fitting method and couplingsimulation database were used for image processing and to calculate optimal coupling efficiency. Under optimal coupling efficiency,the minimum amount of movement of the translation stages was used to calculate the offset of each axle or the coupling efficiencywhen tilted. Moreover, a coupling efficiency database was established. The optical axle center offset in the alignment was calculatedby comparing the data in the database. Finally, the optical axle center offset or tilt direction was identified through the program toachieve the position of optimal coupling efficiency.