Meng    Yang Jiang    Liu Ji    Lee C.    Bello I.    李述汤    

Applied Physics Letters

2003

刘长洪    Yiu W. C.    Frederick wing fai Au    Ding J. X.    Lee C.    李述汤    

Applied Physics Letters

2003

We report here the first synthesis of 2H-polytype silicon carbide (SiC) nanowhiskers by the reaction of silicon monoxide (SiO) with methane. The diameter of the 2H-SiC nanowhiskers was less than 200 nm and the length was over 2 μm. Energy dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM), high resolution TEM (HRTEM) and Raman scattering spectroscopy were used to characterize the nanowhiskers. Electron diffraction and HRTEM confirmed that the nanowhiskers were composed of the rare-occurring 2H-SiC polytype with a 3C-SiC polytype tip. The growth direction of the nanowhiskers was along the hexagonal [0001] orientation. The nanowhiskers had many stacking faults and micro-twins, which possibly caused the downshift of the Raman scattering peaks. The SiC nanowhiskers are believed to form via the oxide-assisted growth process. © 2003 Elsevier B.V. All rights reserved.

Yao Y.    李述汤     李方华   

Chemical Physics Letters

2003

We report the first synthesis of ultrafine zinc sulfide (ZnS) nanowires with a sphalerite structure. Large-area, high- and uniform-density ZnS nanowires were grown on Au-coated silicon substrates by hydrogen-assisted thermal evaporation. The product was analyzed with scanning electron microscopy, X-ray diffraction, transmission electron microscopy and photoluminescence (PL). The ZnS nanowires had a sphalerite structure, a growth direction along [111], diameters of 10-20 nm, and lengths of several micrometers. The PL spectrum of the ZnS nanowires was measured. The growth of the ZnS nanowires was explained with the vapor-liquid-solid model, and their structure could be controlled by the deposition temperature. © 2003 Published by Elsevier B.V.

Meng    Liu Ji    Yang Jiang    Chen W. W.    Lee C.    Bello I.    李述汤    

Chemical Physics Letters

2003

The formation of nanostructures in the matrix of tetrahedral amorphous carbon (ta-C) films induced by ion beam implantation at high doses has been studied by high-resolution transmission electron microscopy, transmission electron diffraction and Raman spectroscopy. The ta-C films were deposited by a filtered cathodic vacuum arc and subsequently implanted by carbon ion beams extracted from a metal vapor vacuum arc ion source. The carbon ions were implanted to doses ranging from 3×10 to 3×10 ions/cm. In accord with the thickness of ta-C films and ion ranges (39-75 nm) required the ion energy was determined to be within a range of 25-50 keV. The analysis of Raman spectra indicates that originally abundant sp carbon atomic bonding of ta-C is gradually converted to a graphitic phase during the course of ion bombardment. The local order, growth and clustering the sp bonded carbon atoms in the ta-C films by ion implantation is also indicated by Raman spectroscopy. However, the analysis of implanted amorphous carbon films on an atomic scale shows the formation of structure with the higher degree of order. The graphitic basal planes are formed preferably along the ion tracks. The results are discussed in the context of previously reported studies of implanted ta-C films and glassy carbon. This article shows a critical damage level of 0.24 displacements per atom when the onset of the transformation occurs and demonstrates that the initially amorphous phase with short ordered sp bonding configuration can be nanostructured to the higher degree of an ordered structure using proper ion energies and doses. © 2003 Elsevier Science B.V. All rights reserved.

Kutsay    Bello I.    Yeshayahu Lifshitz    Lam Christopher Wai-Kei    Luk W. Y.    李述汤     Meng    Kremnican Vladimir   

Diamond and Related Materials

2003

Shiulun Lai    Mei yee Chan    Lee C.    李述汤    

Journal of Applied Physics

2003

Two new anthracene derivatives with red emission have been synthesized. The materials were characterized with photoluminescence spectroscopy, and showed emission peaking at over 600 nm. Organic light-emitting devices were fabricated by using these derivatives as dopants. The devices have a maximum efficiency of 0.6 cd A and an emission peak at 617 nm. The results of color tuning and fluorescent yield enhancement for anthracene derivatives are presented.

Baoxiu Mi    Gao Z. Q.    Liu M. W.    Chan Ka-Yee    Kwong H.    Ningbew Wong    Lee C.    Liangsun Hung    李述汤    

Journal of Materials Chemistry

2002

A diamond nanowire (CNW), a silicon nanowire (SiNW), a carbon nanotube (CNT), and a silicon nanotube (SiNT) were studied using the semiempirical molecular orbital PM3 method, with confirmations by calculations at the HF/3-21G and HF/3-21G(d) levels. It was shown that the systems with a diamond structure generally possess larger band gaps than their tubular counterparts. Carbon nanotubular structure shows efficient sp hybridization and π bonding, thus allowing a high stability of the carbon nanotube structure. In contrast, silicon prefers sp hybridization and favors the tetrahedral diamond-like structures, thereby forming the commonly observed nanowires. This distinction can be traced to the differences in the energetics and overlaps of the valence s and p orbitals of C vs Si. Nevertheless, when the dangling bonds are properly terminated, SiNT can in principle be formed. The resulting energy minimized SiNT, however, adopts a severely puckered structure (with a corrugated surface) with Si-Si distances ranging from 1.85 to 2.25 Å. © 2002 Elsevier Science B.V. All rights reserved.

Ruiqin Zhang    李述汤     Law Chi Kin    Waikee Li    Boon keng Teo   

Chemical Physics Letters

2002

One-dimensional nanostructures of SnO with a ribbonlike morphology have been prepared in large scale via rapid oxidation of elemental tin at 1080 °C. The products were characterized with scanning electron microscopy, X-ray powder diffraction, transmission electron microscopy, Raman scattering, and photoluminescence spectroscopy. The as-synthesized SnO nanoribbons appeared to be single crystals and had preferred [110] and [203] growth directions. The lengths of the nanoribbons were up to several hundreds of micrometers, and the typical width and thickness were in the range of 30-150 nm and 10-30 nm, respectively. The strong photoluminescence of the nanoribbons in the visible region suggested possible applications in nanoscaled optoelectronic devices. A possible growth mechanism for the SnO nanoribbons was proposed.

胡俊青    Xiuliang Ma    Naigui Shang    Zhiyuan Xie    Ningbew Wong    Lee C.    李述汤    

Journal of Physical Chemistry B

2002

Ruiqin Zhang    Lu W. C.    Lee C.    Liangsun Hung    李述汤    

Journal of Chemical Physics

2002