Ning-Bew Wong

Ordered silicon nanowire arrays via nanosphere lithography and metal-induced etching

Two-dimensional silica colloidal crystal template is used to create metal nanohole arrays on a silicon surface, which enables the controlled fabrication of aligned silicon nanowire (SiNW) arrays via metal catalytic etching. By varying the size of silica colloidal crystals, aligned arrays of SiNWs with desirable diameter and density could be obtained. The formation of ordered SiNW arrays is due to selective and anisotropic etching of silicon induced by the silver pattern. The orientation of SiNW arrays is influenced by silver movement in silicon, and the wire axes are primarily along the ⟨100⟩ direction.

β-SiC nanorods synthesized by hot filament chemical vapor deposition

A one-step procedure has been developed to grow β-SiC nanorods from a solid carbon and silicon source on a Si substrate by hot filament chemical vapor deposition. This process is catalyzed by metallic particles which come from impurities in the solid source which is a plate made by pressing a mixture graphite and silicon powders at 150 °C. Hydrogen was introduced into the reaction chamber to react with the solid plate to produce hydrocarbon and hydrosilicon radicals which presumably reacted to form SiC nanorods. The nanorods consisted of a crystalline β-SiC core with an amorphous silicon oxide shell layer and grew along the [100] direction. The nanorods were 10–30 nm in diameter and less than 1 μm in length.

A bis-salicylaldiminato Schiff base and its zinc complex as new highly fluorescent red dopants for high performance organic electroluminescence devices

Schiff base 2,3-bis[(4-diethylamino-2-hydroxybenzylidene)amino]but-2-enedinitrile (BDPMB) and its zinc complex (BDPMB-Zn) with donor–acceptor–donor (D–A–D) type ICT properties in the neutral form were used as novel red-emitting dopants in OLEDs; bright saturated red-emitting EL devices with excellent colour chromaticity coordinates (x, y = 0.670, 0.325 for BDPMB; x, y = 0.655, 0.325 for BDPMB-Zn) and good efficiency (1.35 cd A−1 for BDPMB; 0.50 cd A−1 for BDPMB-Zn) were obtained.

Characterization of zinc oxide crystal whiskers grown by thermal evaporation

Abstract ZnO crystal whiskers were prepared via a simple thermal evaporation of a mixture of ZnS and Fe(NO 3 ) 3 . The growth process was carried out in an alumina tube at 1300°C using Ar mixed with 5% H 2 as the carrier gas. The ZnO whiskers obtained had diameters ranging from 200 to 500 nm and lengths up to several hundreds of micrometers. The photoluminescence spectrum of as-grown ZnO whiskers was studied. The influences of reaction temperature, time, and carrier gases on the formation of the whiskers were investigated. A preliminary growth mechanism of the ZnO crystal whiskers was proposed.

ZnO nanowires array p-n homojunction and its application as a visible-blind ultraviolet photodetector

We demonstrated a simple and low-cost fabrication of ZnO p-n homojunction. The junction consists of n-type ZnO nanowires array by a hydrothermal method covered with p-type Al, N co-doped ZnO film by a sol-gel method. The junction exhibits good rectification characteristics, with reverse leakage current and rectification ratio of ∼5 μA and ∼150 at bias of 3 V, respectively. The junction is operated as a photodetector when light radiation is shined on the glass-side of the device. The photodetector shows a peak responsivity at 384 nm with UV-visible responsivity ratio (R384 nm/R550 nm) of ∼70 at an operating bias of −3 V.

Ag-modified silicon nanowires substrate for ultrasensitive surface-enhanced raman spectroscopy

We report a unique substrate for surface-enhanced raman spectroscopy (SERS) based on silver nanoparticles-embedded silicon nanowires (SiNWs). The SiNWs were prepared by thermal evaporation of SiO powder via oxide-assisted growth, oxide removed with HF, and then used to reduce silver ions to form a highly decorated Ag-embedded surface. Such modified SiNWs substrates yielded ultrahigh SERS sensitivity, which could detect 25μl of 1×10−16M Rhodamine 6G, 1×10−16M crystal violet, and 1×10−14M nicotine in methanol solutions. An Ag-modified SiNW strand could also enable SERS detection of 25μl of 1×10−8mg∕ml calf thymus DNA. The possible mechanisms for the ultrahigh SERS sensitivity were discussed.

A surface-enhanced Raman spectroscopy substrate for highly sensitive label-free immunoassay

Large-scale uniform silicon nanowires (SiNWs) array was fabricated by chemical etching on n-Si(111) wafer. Silver nanoparticles (AgNPs) were loaded on their surfaces. The AgNPs on SiNWs (AgNPs@SiNWs) array exhibit strong surface-enhanced Raman effect. On the substrate surfaces, characteristic Raman signals are generated with trace amount of mouse immunoglobulin G (mIgG), goat-anti-mouse immunoglobulin G (gamIgG), and immune complexes formed from 4ng each of mIgG and gamIgG. The shifted positions and changed intensities in Raman bands indicate the occurrence of immunoreactions. This AgNPs@SiNWs array is a unique substrate for surface-enhanced Raman spectroscopy to show the immune reagents and immunoreactions at higher sensitivity.

Thermal stability of zirconia membranes

Yttria-doped zirconia and pure zirconia membranes were prepared with sol-gel method using zirconium oxychloride octahydrate (ZrOCl2 · 8H2O) as starting material. Characterization for membranes was performed by means of BET, TG-DTA, SEM, XRD, FT-IR and Raman spectroscopy. Stable tetragonal phase and pore structure in yttria-doped zirconia membranes were observed at 400–700°C. And, phase transformation temperature can be retarded to 300°C. As a result, yttria doping can be developed as a method to secure the membrane from cracking in preparation process and high temperature applications.

EPR Study of O3 − on Magnesium Oxide

Molecular oxygen reacts with O− on the surface of magnesium oxide to form the ozonide ion, O3−. The EPR spectrum of this ion was used to verify its formation. Oxygen‐17 was introduced into the molecule either via the O− ion or the O2 molecule. The spectrum is characterized by g1=2.0172, g2=2.0100, and g3=2.0014, with | a3 a |=26 G, | a3 b |=82 G, and | a3 c |=65 G. Here, a3 a is the hyperfine splitting for the oxygen atom which was originally O−. The splitting along the other principal axes was less than 5 G. A model is suggested in which a terminal oxygen of the bent molecule is in the plane of the surface, and the plane of the molecule is perpendicular to the surface. The ozonide ion slowly dissociated at 25° to form O2−. The oxygen‐17 isotope distribution indicates that the superoxide ion was largely derived from molecular oxygen, rather than the O− ion.

Straight β-SiC nanorods synthesized by using C–Si–SiO2

Straight beta-silicon carbide nanorods have been grown on silicon wafers using hot filament chemical vapor deposition with iron particles as catalyst. A plate made of a C–Si–SiO2 powder mixture was used as carbon and silicon sources. Hydrogen, which was the only gas fed into the deposition system, acts both as a reactant and as a mass transporting medium. The diameter of the β-SiC nanorod ranged from 20 to 70 nm, while its length was approximately 1 μm. A growth mechanism of beta-silicon carbide nanorods was proposed. The field emission properties of the beta-silicon carbide nanorods grown on the silicon substrate are also reported.