Browsing by Author "Tsay, Shiow-Fon"

Now showing 1 - 6 of 6

Atomic and electronic structures of thin NaCl films grown on a Ge(001) surface
(2009-07-01)
Tsay, Shiow-Fon
;
Lin, D. -S.
;
物理研究所
;
Institute of Physics
Density functional theory (DFT) with LDA and GGA have been employed to study the interface and thin film properties of NaCl on a Ge(0 0 1) surface. The atomic and electronic structures of thin NaCl films from one to ten monolayers were analyzed. The layer adsorption energies show that a quasi-crystalline (0 0 1) fcc NaCl film is built up via a layer-by-layer growth mode with NaCl thickness above 2 ML. Simulated STM images show a well-resolved (1 x 1) NaCl atomic structure for sample bias voltage V(s) < -2.5 V and the bright protrusions should be assigned to the Cl(-) ions of the NaCl film. The Ge substrate dimer is reserved and buckled like a clean Ge(0 0 1)-p(2 x 2) surface as the result of weak interface interaction between the dangling bonds coming from valence pi states of the Ge substrate and the 3p states of the interfacial Cl(-) ion. These results are consistent with the experiments of STM, LEED and EELS. (C) 2009 Elsevier B.V. All rights reserved.
Correlation of reaction sites during the chlorine extraction by hydrogen atom from Cl/Si(100)-2X1
(2007-07-21)
Hsieh, Ming-Feng
;
Chung, Jen-Yang
;
Lin, Deng-Sung
;
Tsay, Shiow-Fon
;
物理研究所
The Cl abstraction by gas-phase H atoms from a Cl-terminated Si(100) surface was investigated by scanning tunneling microscopy (STM), high-resolution core level photoemission spectroscopy, and computer simulation. The core level measurements indicate that some additional reactions occur besides the removal of Cl. The STM images show that the Cl-extracted sites disperse randomly in the initial phase of the reaction, but form small clusters as more Cl is removed, indicating a correlation between Cl-extracted sites. These results suggest that the hot-atom process may occur during the atom-adatom collision. (C) 2007 American Institute of Physics.
Dynamic structure factor of liquid Ga close to the melting point: spectral linewidth at high momentum transfer
(2007-05-23)
Tsai, K. H.
;
Wu, Ten-Ming
;
Tsay, Shiow-Fon
;
Yang, Tzong-Jer
;
電子物理學系
By simulating an interatomic pair potential obtained from the first-principles generalized energy-independent nonlocal model-pseudopotential (GEINMP) theory, we have reproduced the high-wavevector shoulder in the static structure factor and the recently observed anomaly in the linewidth of the dynamic structure factor of liquid Ga close to the melting point. Our results indicate that the two anomalies have the same physical origin, which is associated with the Friedel oscillations induced by conduction electrons. The anomaly in the dynamics can be well described by the revised Enskog theory for the hard-sphere (HS) system, with the effective HS diameter determined by the position at the first peak of the radial distribution function. We interpret the occurrence of the anomaly in the dynamics by the physical picture of cage diffusion.
Possibility of direct exchange diffusion of hydrogen on the Cl/Si(100)-2X1 surface
(2009-07-01)
Hsieh, Ming-Feng
;
Lin, Deng-Sung
;
Tsay, Shiow-Fon
;
物理研究所
;
Institute of Physics
The diffusion behavior of hydrogen substitutional sites on the chlorine-terminated Si(100) surface was investigated at elevated temperatures using time-lapse scanning tunneling microscopy (STM). STM movies show that each hydrogen atom undergoes Brownian motion within a monochloride dimer row. The position of a hydrogen substitutional site is exchanged directly with that of an immediate neighboring chlorine atom in either the same dimer (intradimer diffusion) or in one of the two adjacent dimers in the same row (intrarow diffusion). Accordingly, conceptual direct exchange diffusion (DED) in a two-dimensional lattice was experimentally observed. Analysis of STM movies at various temperatures yielded rather low attempt frequencies and energy barriers, leading to the suggestion that the diffusion mechanism involves an intermediate low-energy molecular state. Density-functional theory (DFT) calculations were also performed and provided partial support for the proposed diffusion mechanism.
Revisiting anomalous structures in liquid Ga
(2010-01-21)
Tsai, K. H.
;
Wu, Ten-Ming
;
Tsay, Shiow-Fon
;
物理研究所
;
Institute of Physics
In terms of an interatomic pair potential, which well characterizes the dynamic properties of liquid Ga, we investigate again the origin of the well known high-q shoulder in the static structure factor of the liquid. Similar to the results of Gong's simulation at high temperature, dimers with extremely short bond lengths are indeed found in our model just above the melting point, but our results indicate that it is unlikely for the high-q shoulder to be produced by these dimers. Instead, based on our model, the high-q shoulder is resulted from some medium-range order, which is related to the structures beyond the first shell of the radial distribution function, caused by Friedel oscillations within a nanoscale range.
Simulations for the time evolution of instantaneous resonant modes: Creation, annihilation and mode exchange
(2006-11-15)
Wu, Ten-Ming
;
Chang, S. L.
;
Tsay, Shiow-Fon
;
Tsai, K. H.
;
物理研究所
In this paper, we simulate the time evolution of the instantaneous resonant modes (IRMs), which are quasilocalized, in a model of Ga liquid. Through the simulations, we have observed the whole process from creation to annihilation of each individual IRM, and its lifetime is, therefore, estimated. We also find the exchange in character between an IRM and a non-resonant instantaneous normal mode (INM). The exchange occurs as the two INMs have very close frequencies and share a common central particle. (c) 2006 Elsevier B.V. All rights reserved.