Browsing by Author "Ju, Shin-Pon"

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Adsorption and dissociation of the HCl and Cl-2 molecules on W(111) surface: A computational study
(2008-08-14)
Chen, Hui-Lung
;
Ju, Shin-Pon
;
Chen, Hsin-Tsung
;
Musaev, Djamaladdin G.
;
Lin, M. C.
The adsorption and dissociation of Cl-2 and HCl molecules on W(111) surface have been studied at the density functional theory (DFT) level in conjunction with the projector augmented wave (PAW) method. The molecular structures and surface-adsorbent interaction energies of W(111)/Cl, W(111)/H, W(111)/Cl-2, and W(111)/HCl systems are predicted. In these studies, four adsorption sites, such as top (T), bridge (B), shallow (S), and deep (D) sites, of the W(111) surface are considered. It is shown that the Cl-2 and HCl molecules adsorb to the W(111) surface by the end-on manner (by their Cl-Cl or H-Cl bonds perpendicular to the W surface), and their dissociative adsorptions occur without intrinsic energy barriers and are exothermic by 80.46 and 53.72 kcal/mol, for Cl-2 and HCl, respectively. Molecular dynamics studies show that the dissociation of Cl-2 and HCl molecules on the W(111) surface occur in asymmetric fashion: at the beginning adsorbate forms a strong bond between one of their atoms and W centers, followed by the dissociation of the Cl-Cl (and/or H-Cl) bond and formation of the second bond between the atoms of adsorbate and the W center. For the Cl-2 molecule, both Cl atoms are preferred to adsorb at the top W centers. For the HCl molecule, after the dissociation of the H-Cl bond the Cl atom still occupies the top adsorption site, but the H atom prefers to move to the position between the top and shallow W centers. The rate constants for the dissociative adsorption of Cl-2 and HCl have been predicted with variational RRKM theory.
Density Functional Studies of the Adsorption and Dissociation of NO(x) (x=1, 2) Molecules on the W(111) Surface
(2009-04-02)
Chen, Hsin-Tsung
;
Chen, Hui-Lung
;
Ju, Shin-Pon
;
Musaev, Djamaladdin G.
;
Lin, M. C.
Adsorption and dissociation of NOx (x = 1, 2) molecules on the W(111) surface have been investigated by using the density functional theory (DFT) with the projector-augmentcd wave (PAW) approach in periodic boundary conditions. The adsorption structures, vibrational frequencies, and binding energies of NO(2), NO, N, and 0 on the W(111) surface were predicted. It was shown that the most favorable adsorption geometry of W(111)/NO(2) is the WNO(2) (IV-mu(3)-N2, OI, OI) configuration with NO(2) at the 3-fold-shallow site of the surface and has an adsorption energy of 79.4 kcal/mol. For W(111)NO, WNO(II-mu(2)-N1, O1) with NO at the bridge site is energetically the most favorable one and has an adsorption energy of 74.4 kcal/mol. The N and 0 atoms are bound preferentially at the bridge and top sites, respectively. The potential energy profiles for the decomposition of NO(2) on W(111) were constructed using the nudged elastic band (NEB) method. The barriers for the stepwise NO(2)-deoxygenation process to N((ads)) + 20((ads)) are calculated to be only 0.5-3.7 (for the first step of the reaction, ON-O bond activation) and 0.2-3.0 (for the second step of the reaction, N-O bond activation of the coordinated NO molecule) kcal/mol, with an overall exothermicity of 177.0-185.2 kcal/mol. These findings show that NO,) can easily decompose on the W(111) surface. The rate constants for NO(2) and NO dissociation on the surface were also predicted.
Density Functional Studies of the Adsorption and Dissociation of NOx (x=1, 2) Molecules on the W(111) Surface
(2009-04-02)
Chen, Hsin-Tsung
;
Chen, Hui-Lung
;
Ju, Shin-Pon
;
Musaev, Djamaladdin G.
;
Lin, M. C.
Adsorption and dissociation of NOx (x = 1, 2) molecules on the W(111) surface have been investigated by using the density functional theory (DFT) with the projector-augmentcd wave (PAW) approach in periodic boundary conditions. The adsorption structures, vibrational frequencies, and binding energies of NO2, NO, N, and 0 on the W(111) surface were predicted. It was shown that the most favorable adsorption geometry of W(111)/NO2 is the WNO2 (IV-mu(3)-N2, OI, OI) configuration with NO2 at the 3-fold-shallow site of the surface and has an adsorption energy of 79.4 kcal/mol. For W(111)NO, WNO(II-mu(2)-N1, O1) with NO at the bridge site is energetically the most favorable one and has an adsorption energy of 74.4 kcal/mol. The N and 0 atoms are bound preferentially at the bridge and top sites, respectively. The potential energy profiles for the decomposition of NO2 on W(111) were constructed using the nudged elastic band (NEB) method. The barriers for the stepwise NO2-deoxygenation process to N-(ads) + 20((ads)) are calculated to be only 0.5-3.7 (for the first step of the reaction, ON-O bond activation) and 0.2-3.0 (for the second step of the reaction, N-O bond activation of the coordinated NO molecule) kcal/mol, with an overall exothermicity of 177.0-185.2 kcal/mol. These findings show that NO,) can easily decompose on the W(111) surface. The rate constants for NO2 and NO dissociation on the surface were also predicted.
Kinetics and Mechanisms for the Adsorption, Dissociation, and Diffusion of Hydrogen in Ni and Ni/YSZ Slabs: A DFT Study
(2012-04-03)
Weng, Meng Hsiung
;
Chen, Hsin-Tsung
;
Wang, Yao-Chun
;
Ju, Shin-Pon
;
Chang, Jee-Gong
The adsorption, dissociation, and diffusion of hydrogen in Ni(100) and Ni(100)/YSZ(100) slabs with two different interfaces (Ni/cation and Ni/O interface) have been studied by the density functional theory (DFT) with the Perdew-Wang functional. The H-2 molecule is found to preferentially absorb on a Top (T) site with side-on configuration on the Ni(100) surface, while the H-atom is strongly bound at a fcc Hollow (H) site. The barrier for the H-2 dissociation on both surfaces is calculated to be only similar to 0.1 eV. The potential energy pathways of H diffusion on pure Ni and Ni/YSZ with the two different interfaces are studied. Our calculated results show that the H-atom diffusion occurs via surface path rather than the bulk path. For the bulk path in Ni/YSZ, H-atom migration can occur more readily at the Ni/cation interface compared to the Ni/O interface. The existence of vacancy in the interface region is found to improve the mobility of H-atoms at the interface of Ni/YSZ slab. The rate constants for hydrogen dissociation and diffusion in pure Ni and Ni/YSZ are predicted.
Surface morphological and nanomechanical properties of PLD-derived ZnO thin films
(2008-05-01)
Jian, Sheng-Rui
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Teng, I-Ju
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Yang, Ping-Feng
;
Lai, Yi-Shao
;
Lu, Jian-Ming
This study reports the surface roughness and nanomechanical characteristics of ZnO thin films deposited on the various substrates, obtained by means of atomic force microscopy (AFM), nanoindentation and nanoscratch techniques. ZnO thin films are deposited on (a- and c-axis) sapphires and (0001) 6H-SiC substrates by using the pulsed-laser depositions (PLD) system. Continuous stiffness measurements (CSM) technique is used in the nanoindentation tests to determine the hardness and Young's modulus of ZnO thin films. The importance of the ratio (H/E-film) of elastic to plastic deformation during nanoindentation of ZnO thin films on their behaviors in contact-induced damage during fabrication of ZnO-based devices is considered. In addition, the friction coefficient of ZnO thin films is also presented here.