Papers by Author: Yuan Ming Huang

Abstract: Metal-semiconductor Zn/ZnO core-shell structures are fabricated by a simple ultrasonic process of raw Zn particles in water. The crystal structure, morphologies and fluorescence of the Zn/ZnO core-shell particles are characterized with X-ray diffraction (XRD), scanning electronic microscopy (SEM) and fluorescence spectrophotometer. The XRD pattern confirms that the shells of the Zn/ZnO core-shell particles are composed of Wurtzite ZnO crystals. The SEM study clearly exhibits the formation of ZnO on the surface of Zn spheres. The room-temperature fluorescence spectra have been observed a strong ultraviolet (UV)-visible emission at 381 nm and a yellow-green deep-level emission at about 534 nm. It is noted that the very broad green emission at 510 nm appears in the ZnO crystals with increasing the content of ZnO shell on the surface of Zn spheres. Furthermore, a possible formed mechanism of ZnO shells on the Zn core is discussed.

Abstract: Zinc oxide (ZnO) was synthesized by solid-liquid reaction of raw Zn particles in water. The synthesized ZnO were characterized with X-ray diffraction (XRD), scanning electronic microscopy (SEM) and photoluminescence (PL) spectrophotometer. The XRD pattern confirmed that the formation of ZnO with wurtzite structure and ZnOOH crystals. The SEM study clearly exhibited a honeycomb-shaped structure of the Zn/ZnO/ZnOOH composites. Room-temperature PL spectra have been observed a very weak UV emission at 376 nm and a very strong yellow-green emission at 538 nm. Furthermore, a possible mechanism of the water-assisted conversion of ZnO from metallic Zn particles was discussed.

Abstract: A polyvinyl alcohol (PVA) nanocomposite thin film embedded with zinc sulfide (ZnS) quantum dots was fabricated by a drop-casting method. The ZnS-embedded PVA films were characterized with polarized optical microscopy (POM), ultraviolet-visible (UV-vis) spectroscopy and photoluminescence (PL) spectroscopy. The POM study clearly exhibits the photo-elasticity effects of the ZnS/PVA film when stress is added. Optical absorption spectra showed strong red shift for the ZnS quantum dots in the PVA matrix. Room-temperature PL spectra demonstrated that the pure ZnS quantum dots show cyan emission at 517 nm while ZnS/PVA thin film gives off blue PL with a strong broad peak at 478 nm and a shoulder peak at 536 nm.

Abstract: Controlling the photon propagation in materials by photonic crystals lies at the heart of quantum optics. The motivation of our work is to investigate the direct control of the photon confinement in the self-assembled two-dimensional SiO2 photonic crystals. Here we demonstrate the realization of transmitted light controls in the self-assembled two-dimensional SiO2 PCs. Our experimental results agree well with the theoretical calculations on the photonic band gaps in the spectral region of 400-1100 nm. These results present experimental evidence on the direct control of the photon confinement in the self-assembled two-dimensional SiO2 PCs.

Abstract: Porous silicon based visible light photodetectors with the characteristic structures of Al/porous silicon/Si were developed by evaporating aluminum contact onto the top surface of porous silicon films to form metal-semiconductor-metal Schottky junctions. The spongy nanostructures of the porous silicon film were characterized with the scanning electron microscopy. The current-voltage characteristics, the biased voltage dependent photocurrents and the illumination intensity dependent photocurrents were measured for the Al/porous silicon/Si visible light photodetectors. It is found that the photocurrents as large as 4 mA/cm2 can be achieved for the porous silicon based visible light photodetectors under the normal illumination of one 500 W tungsten lamp

Abstract: The effect of sodium chloride on the sol-gel synthesized silica colloidal particles has been investigated. The silica colloidal particles in the size range of 420-800 nm were synthesized from the hydrolysis and condensation of tetraethyl orthosilicate by varying the amount of sodium chloride from 15 to 30 mg while keeping the tetraethyl orthosilicate (20 ml), ethanol (125 ml), ammonia (6 ml) and distilled water (18 ml) fixed. Scanning electron microscopy (SEM) was employed to analyze the morphology of the synthesized silica particles. Our results demonstrated that: (1) sticky and spongy silica spheroids were resulted if the amount of sodium chloride was less than 15 mg; (2) spherical silica particles were resulted with good monodispersity when the amount of sodium chloride was in the range of 22-24 mg; and (3) silica spheres were obtained but with a wide size distribution when the amount of sodium chloride was more than 26 mg.

Abstract: Upon the 325 nm excitation from a helium-cadmium laser, the photoluminescence (PL) from aged porous silicon was investigated with fluorescence spectroscopy. Each PL spectrum of the aged porous silicon films contained two luminescent bands, one of the luminescent bands peaked at about 466.7 nm whereas the other luminescent band peaked at about 596.1 nm. The origin of the blue PL from aged porous silicon was discussed, and our results indicated that the blue photoluminescence of porous silicon films originated from the silicon oxide itself.

Abstract: Soluble polypyrrole was obtained by naturally oxidizing pyrrole in air at room temperature for one to four years. Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy and ultraviolet-visible absorption spectroscopy were employed to characterize the chemical structures of the naturally oxidized polypyrrole. The electroluminescence from the naturally oxidized polypyrrole was recorded. The electroluminescence of the naturally oxidized polypyrrole was broad with its peak located at about 480 nm. Prototyped thin-film display panels were developed using the naturally oxidized polypyrrole as active medium.

Abstract: A rod-like liquid crystal (LC) N,N-(terephthalylidene) bis (4-n-butylaniline) (TB4A) was synthesized by one step at room temperature. The synthesized TB4A were investigated with nuclear magnetic resonance, fourier transform infrared spectrometer and ultraviolet-visible spectrophotometry, differential scanning calorimetry and polarizing optical microscopy. Our results demonstrated that the TB4A can form nematic, smectic A, smectic C, smectic F and smectic G LC phases.

Abstract: With polarizing optical microscopy we have investigated the electro-optic properties of a nematic liquid crystal 4-n-pentyl-4′-cyanobipheny confined in the microchannels of porous silicon. Experimental study shows clearly that the liquid crystal molecules tend to align parallel to the direction of the pore columns in porous silicon. Schlieren textures with S = +1 and +2 disclinations were recorded. Our experimental investigations show that uniaxial alignment, the planar radial and the escaped radial configurations exist around the given microchannels of porous silicon.