Economic basis sets for ab initio calculations of systems involving titanium (Ti) atom have been studied. The basis set in which the polarization and diffuse functions are applied only to Ti and its nearest neighboring atoms is shown to give reliable binding energies and geometries for various carbon-based compounds. Such a basis set is used as the economic basis set for calculations of medium-sized clusters simulating Ti and diamond interactions. For large clusters composed of Ti and C atoms, the more economic basis set 6-31G is considered for obtaining reliable energetics with the correction using high-level single-point energy calculations with 6-31+G*. The approach to determine the economic basis set is expected to be useful for a general system containing transition metal element. With the economic basis sets, simulations of diamond metallization have revealed reasonable behavior of the Ti atomic interaction with diamond film. On the basis of the determined energetics of Ti deposition, the high Ti concentration in CVD diamond after metallization is conjectured to occupy the grain boundaries rather than the bulk of diamond grain. For a Ti atom with high kinetic energy, the Ti atom may penetrate through a diamond (001) surface more easily than through a diamond (1 1 1) surface. In the diamond bulk, the Ti atom may energetically favor to substitute a C site more than diffusion.
Ruiqin Zhang Lu W. C. Cheung H. F. 李述汤
Journal of Physical Chemistry B
2002
β-SiC nanowires has been grown from SiO thin films deposited on Si (100) substrate at 1300 °C. A plate of graphite was used as the only carbon source. Argon was the only gas fed into the system. Structural and optical properties of the SiC nanowires were investigated using scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. It was found that the as-grown SiC nanowires are nearly free from undesirable thick oxide shell typically found on SiC nanowires synthesized by other methods. The present approach has also the potential advantage of highly selective growth on patterned substrate. © 2002 Elsevier Science B.V. All rights reserved.
Li J. C. Lee C. 李述汤
Chemical Physics Letters
2002
Potential applications of Ytterbium (Yb) in cathode system for organic optoelectronic/electronic devices were explored in NPB/Alq based bi-layer organic light-emitting devices (OLEDs). When a thin (14.5 nm) Yb layer capped with a thicker (200 nm) Ag layer was used as the cathode, the OLEDs show enhanced electron injection over those using the standard Mg:Ag cathode. Performance of the OLEDs with the Yb/Ag cathode is comparable to that using LiF/Al cathode. Interestingly, we also found that Yb can also be used to prepare a highly transparent cathode by coevaporating Yb and Ag to form a Yb:Ag alloy electrode. Surface-emitting (or top emission) and transparent (emission from both surfaces) OLEDs with low turn-on voltage (3.75 V) and high efficiency were prepared with the Yb:Ag electrode. © 2002 Elsevier Science B.V. All rights reserved.
Shiulun Lai Mei yee Chan 冯敏强 Lee C. Liangsun Hung 李述汤
Chemical Physics Letters
2002
Ultrafine and uniform silicon nanowires (SiNWs), with a Si crystalline core of 1-5 nm (average 3 nm) in diameter and a SiO outer layer of 10-20 nm thick, were synthesized by the oxide-assisted growth method via the disproportionation of thermally evaporated SiO using zeolite as a template/precursor. From transmission and secondary electron microscopic characterizations, we deduced that the zeolite acted to limit the lateral growth of the Si crystalline core and supply the excess oxide to form the thick oxide outer layer. The ultrafine SiNWs exhibited strong photoluminescence that peaked at 720 nm. © 2002 Elsevier Science B.V. All rights reserved.
Li Xuhui Sun Ningbew Wong Lee C. 李述汤 Boon keng Teo
Chemical Physics Letters
2002
Ma Dongge Fushun Liang Li xiang Wang 李述汤 Liangsun Hung
Chemical Physics Letters
2002
In an attempt to provide ohmic contacts to silicon nanowires (SiNWs), SiNWs wrapped with Au film have been fabricated. Au particles were deposited on the as-grown SiNWs and followed by electron beam annealing under transmission electron microscopy (TEM). The high-resolution TEM (HRTEM) study showed the transformation of the Au particles into crystalline Au film. The uniformity of Au film was dependent upon the size and the separation of the Au particles.
Li Xuhui Sun Wong N. B. Lee C. 李述汤 Boon keng Teo
Journal of Physical Chemistry B
2002
Transient electroluminescence (EL) from organic bilayer devices having different N-arylbenzimidazole derivatives as electron-transporting layers (ETLs) was investigated. Using a short voltage pulse as an excitation source, the delay time for the EL was measured and interpreted as the electron transit time across the electron-transporting layer. Electron-mobility can therefore be extracted by considering the luminance mechanism within the devices. The electron-mobilities of the three N-arylbenzimidazole derivatives thus deduced are in the range of 10-10cm/Vs and are comparable to that of the widely used tris-(8-hydroxyquinoalate) aluminum. © 2001 Elsevier Science B.V.
Wong T. C. Kovac Jaroslav Lee C. Liangsun Hung 李述汤
Chemical Physics Letters
2001
Thin films of tris-(8-hydroxyquinoline) aluminum (Alq) were exposed to trace amounts of O, CO, HO, or to ambient air. Evolution of electronic structures of Alq films with increasing gas exposure was measured using ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy (XPS). The vacuum energy level, the highest occupied molecular orbital, and XPS core levels of the constituting elements in Alq shifted according to the kind of gas exposure. Chemical reaction between oxygen and the Alq films was observed upon oxygen exposure. Moreover, it was found that the dominant influence of ambient conditions on the electronic structures of the Alq films was from HO. © 2001 Elsevier Science B.V.
Liao L. S. Xuhui Sun Cheng L. F. Ningbew Wong Lee C. 李述汤
Chemical Physics Letters
2001
Ruiqin Zhang Chu T. S. 李述汤
Journal of Chemical Physics
2001
The chemical reactivity of hydrogen-passivated surface of silicon nanowires (SiNWs) towards the reductive deposition of silver and copper ions from solution is reported. SiNWs synthesized by laser ablation were used in the investigation. The surface properties of SiNWs after the removal of the surface oxide were studied. It is found that the surface silicon of the SiNWs can readily reduce silver (I) and copper (II) ions to metal aggregates of various morphologies on the SiNW surface at room temperature. The reaction products have been characterized with scanning electron microscopy, energy dispersive x-ray spectroscopy, high-resolution transmission electron microscopy, electron energy loss spectroscopy, and x-ray photoelectron spectroscopy. By varying the concentration of Ag(I) ions in the solution, nanostructures of silver with different shapes and sizes can be obtained. This approach for synthesis of metal nanostructures offers a potential method for the preparation of desired metal catalysts. © 2001 American Institute of Physics.
Xuhui Sun Hongying Peng Yuanhong Tang 师文生 Ningbew Wong Lee C. 李述汤 Tsunkong Sham
Journal of Applied Physics
2001