Wei, C. M., Hong I. H., Jeng P. R., Shyu S. C., & Chou Y. C.
(1994).
DIRECT ATOMIC IMAGING USING EXPERIMENTAL MULTIPLE-ENERGY KIKUCHI ELECTRON PATTERNS.
Physical Review B. 49, 5109-5112., Feb, Number 7
AbstractWe demonstrate a direct surface structural tool with high resolution of approximately 1 angstrom in all directions by direct Fourier transformation of measured Kikuchi patterns using a multiple-energy phase-summing method. In this method, with an integral over continuous energy spectra in each direction, both the forward- and backward-scattering oscillations are selected for Fourier transformation by varying the energy range and size of the grid. High-fidelity and artifact-free three-dimensional images of Ag atoms for (100) and (111) single-crystal surfaces are obtained.
Wei, C. M., Gross A., & Scheffler M.
(1998).
Ab initio calculation of the potential energy surface for the dissociation of H-2 on the sulfur-covered Pd(100) surface.
Physical Review B. 57, 15572-15584., Jun, Number 24
AbstractThe presence of sulfur atoms on the Pd(100) surface is known to hinder the dissociative adsorption of hydrogen. Using density-functional theory and the full-potential linear augmented plane-wave method, we investigate the potential energy surface (PES) of the dissociative adsorption of H-2 On the sulfur covered Pd(100) surface. The PES is changed significantly compared to the dissociation on the clean Pd(100) surface, particularly for hydrogen close to the S atoms. While the hydrogen dissociation at the clean Pd(100) surface is nonactivated, for the (2 x 2) sulfur adlayer (coverage Theta (S) = 0.25) the dissociation of H-2 is inhibited by energy barriers. Their heights strongly depend on the distance between the hydrogen and sulfur atoms leading to a highly corrugated PES. The largest barriers are in the vicinity of the sulfur atoms due to the strong repulsion between sulfur and hydrogen. Still the hydrogen dissociation on the (2x2) sulfur covered Pd(100) surface is exothermic. Thus the poisoning effect of sulfur adatoms for H-2 dissociation at low sulfur coverage (Theta(S) less than or equal to 0.25) is mainly governed by the formation of energy barriers, not by blocking of the adsorption sites. For the c(2 x 2) sulfur adlayer (Theta(S)= 0.5), the PES for hydrogen dissociation is purely repulsive. This is due to the fact that for all different possible adsorption geometries the hydrogen molecules come too close.to the sulfur adatoms before the dissociation is completed.
Wei, C. M., Cheng C., & Chang C. M.
(2006).
Transition between icosahedral and cuboctahedral nanoclusters of lead.
Journal of Physical Chemistry B. 110, 24642-24645., Dec, Number 48
AbstractWe have used ab initio methods to study the possible transition between icosahedral (ico) and cuboctahedral (fcc) structures in lead nanoclusters of sizes up to 309 atoms. Spontaneous fcc-to-ico transition in Pb-13 was observed in the ab initio molecular dynamics (MD) simulations at various temperatures. The transition path can be described predominantly by an angular variable s, which can, generally be applied to the similar transitions in clusters of larger sizes and was observed to follow the Mackay model. We have calculated the two-dimensional energy surface that describes the transition in Pb-13 and found a barrierless fcc-to-ico transition path, which is consistent with the observed spontaneous transition in the ab initio MD simulations. The atomic displacements in the transition were identified as one of the vibrational eigenmodes of these two Pb-13 clusters. For clusters of larger sizes (Pb-n, where n = 55, 147, and 309), the possible transitions following similar paths were determined not to be barrierless and the sizes of the barriers were determined by the ab initio elastic band method.
Wei, P. - C., Bhattacharya S., Liu Y. - F., Liu F., He J., Tung Y. - H., Yang C. - C., Hsing C. - R., Nguyen D. - L., Wei C. - M., Chou M. - Y., Lai Y. - C., Hung T. - L., Guan S. - Y., Chang C. - S., Wu H. - J., Lee C. - H., Li W. - H., Hermann R. P., Chen Y. - Y., & Rao A. M.
(2019).
Thermoelectric Figure-of-Merit of Fully Dense Single-Crystalline SnSe.
ACS OMEGA. 4, 5442-5450., {MAR}, Number {3}
Abstract
Wei, C. M., Tong S. Y., Wedler H., Mendez M. A., & Heinz K.
(1994).
DIRECT STRUCTURAL DETERMINATION BY INVERSION OF EXPERIMENTAL DIFFUSE LOW-ENERGY-ELECTRON DIFFRACTION INTENSITIES.
Physical Review Letters. 72, 2434-2437., Apr, Number 15
AbstractWe demonstrate that two-dimensionally resolved diffuse low-energy electron diffraction intensities can be measured with sufficient accuracy and at multiple energies to allow direct inversion for a low coverage (5%) disordered K/Ni(100) surface. The data inversion reveals three-dimensional coordinates of atoms with atom images whose full width at half maximum is less than 1 angstrom in all spatial directions. By varying the angle of incidence, first layer and second layer near-neighbor Ni atoms are separately imaged. This is the first demonstration of multiple-energy internal-source electron holography using measured elastically backscattered electrons.
Wei, C. M., Yuan J. M., & Tsong T. T.
(1995).
FRACTAL DISSOCIATION DYNAMICS OF DIATOMIC IONS IN A DC FIELD.
Physica A. 221, 297-313., Nov, Number 1-3
AbstractFollowing our previous work, we carry out a more detailed study of dissociation dynamics of diatomic ions field-evaporated from a metallic tip of field-ion microscopy, We have found that the partial fractal behavior of the dissociation probability near threshold field strength and the multiple peaks in the time-of-flight spectrum can be attributed to different combinations of vibrational and rotational cycles before ions dissociate, But more clear revelation of the origin of the fractal behavior comes from investigating the uniform-field limit, where we show that two types of chaos exist, one is associated with the rotational saddle orbit and the other associated with the moving potential barrier of a DC field-distorted anharmonic oscillator, The homoclinic tangles associated with these saddles give rise to the sensitive dependence of dynamics on initial conditions.
Wei, C. M., & Tong S. Y.
(1992).
DIRECT ATOMIC-STRUCTURE BY HOLOGRAPHIC DIFFUSE LEED.
Surface Science. 274, L577-L582., Aug, Number 3
AbstractA multiple-energy phase-summing method is applied to diffuse low-energy electron diffraction intensity spectra to obtain three-dimensional images of surface atoms. In this demonstration, calculated DLEED intensity spectra from a multiple scattering method are directly inverted to produce high-fidelity 3D images of near-neighbor atoms measured from an adatom. No prior knowledge of adsorption site, bond length, bond angle, or type of atom is needed. The images are essentially free from artifacts and have a spatial resolution of approximately 1 angstrom when viewed along any cut-plane. These results demonstrate that holographic DLEED has the potential of being an accurate and direct structural tool for low-density disordered adsorption systems.
Wu, H. C., Chou L. W., Wang L. C., Lee Y. R., Wei C. M., Jiang J. C., Su C., & Lin J. C.
(2008).
Adsorption and desorption of stilbene from the Ag/Ge(111)-root 3 surface.
Journal of Physical Chemistry C. 112, 14464-14474., Sep, Number 37
AbstractThe adsorption and desorption of stilbene on Ag/Ge(111)-(root 3 x root 3)R30 degrees (Ag/Ge(111)-root 3) were investigated using low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), temperature-programmed desorption (TPD), and density functional theory (I)FT). Both trans- and cis-stilbenes form a (2 x 1) overlayer structure on Ag/Ge(111)-root 3 at a coverage of similar to 1 ML. The STM images show parallel strips with three equivalent directions, indicating a self-ordered molecular structure. At a coverage of less than I ML, the TPD of cis-stilbene shows only one peak, attributed to submonolayer desorption. The TPD peaks are indistinguishable for desorption of trans-stilbene from the surface submonolayer and multilayer. This is due to the simultaneous desorption and/or thinning of adsorbed multilayers during the TPD process, as determined from the STM analysis of adsorbed trans-stilbene structures before and after annealing. The TPD traces fit the half-order kinetics for molecular desorption of stilbene from Ag/Ge(111)-root 3 with desorption energies of 20.1 (cis-) and 21.3 kcal/mol (trans-), which are comparable with the calculated values using the DFT method. A plausible explanation for the stilbene desorption process on Ag/Ge(111)-root 3 is proposed and discussed.