Solid State Phenomena Vols. 121-123

Abstract: A new approach to obtain Si nanostructures on insulating layer is proposed by laser irradiation on ultra-thin hydrogenated amorphous silicon (a-Si:H) films with subsequently thermal annealing. It was found that the surface nanostructuring was occurred when the laser fluence exceeded the threshold value as revealed by AFM images. The size and area density of formed Si nanostructures were depended on the laser fluence and film thickness while thermal annealing played an important role in the size and its distribution. The results showed that a high density (>1011cm-2) Si nanostructures with average lateral size of 10-20nm can be achieved by the present technology.

Abstract: Little was known about porous Ge until recently; here some substantial progress in producing porous Ge will be reported, mostly for the first time. i) n-type Ge in aqueous solution: Pore geometries, morphologies and growth peculiarities were found to be quite different from other semiconductors, such as Si and III-V. Nucleation is generally difficult, the preferred growth direction is <100> (and <111>), major stop planes are of the {110} type, but others are also found. In addition, there is always a strong electropolishing component compromising pore geometry and stability. ii) n- and p-type Ge in organic solution: In DMSO solution, the growth direction is <111>, and the stopping planes are still mainly {110}; somewhat unexpected, because this has never been observed in Si, and because no pores have been found in other p-type semiconductors so far, with the exception of Si. Nucleation seems to be difficult too, and new domain-forming phenomena are observed. Smooth or rough pore walls can be obtained, dependent on the experimental conditions.

Abstract: Nanoparticles of anatase TiO2 doped with 2 at.% Sc3+ and 2 at.% V5+ ions were synthesized by sol-gel method. Average crystal sizes of TiO2, TiO2+2 at.% Sc, TiO2+2 at.% V and TiO2+2 at.% (Sc+V) calculated from XRD patterns are 18.0, 16.9, 18.0, 16.2 nm, respectively. HRTEM images of TiO2 and TiO2+2 at.% (Sc+V) exhibit well-defined lattice fringe. The lattice spacings of TiO2 and TiO2+2 at.% (Sc+V) are both measured to be 3.3 Å, which correspond to the distance between the (101) planes of anatase TiO2. Raman spectra of the samples demonstrate the well dispersion of Sc3+ and V5+ ions in the TiO2 matrix. UV-vis diffuse reflectance absorption spectra of the samples show the characteristics of TiO2, and the diffuse reflectance spectra of TiO2+2 at.% V and TiO2+2 at.% (Sc+V) exhibit red shifts and weak wide absorptions in the visible region of 400-600 nm.

Abstract: Flake-shaped hematite (α-Fe2O3) nanostructure has been successfully fabricated by using a hot-plate to directly heat Fe foil or Fe-coated substrates in air at 300oC. After heating, the surface of the samples was found to be populated with α-Fe2O3 nanoflakes. Such growth of α-Fe2O3 nanoflakes was very substrate-friendly. They can be formed on blank Si wafer, patterened Si, AFM tips, silica sphere, quartz, glass slide, Al foil and electrochemically etched W tip. The formation process and the final products were investigated by glancing angle x-ray diffraction (GAXRD), micro-Raman, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate the final products are single crystalline α-Fe2O3 nanoflakes vertically standing on the Fe3O4 film that acts as the precursor for growth of α-Fe2O3. The α-Fe2O3 nanoflakes formed by this method show very sharp tip with the tip radii as small as several nanometers and large surface to volume ratio. Such nanoflakes may be potentially useful as novel candidates for future electron field emission and gas senor devices. Furthermore, it is believed that this simple and substrates-friendly method is useful in extending the applications of α-Fe2O3 nanostructures.

Abstract: Currently there are several models discussed to describe the formation of monodispersed silica particles. Monodisperse colloidal silica was prepared from tetraethoxysilane in mixture of ammonia, water and ethanol. Chemical system reaction permits the controlled growth of silica nanoparticles and subsequent condition of silicic acid in alcoholic solution. The molar ratio of NH4OH, C2H5OH and H2O has a significant effect on particle size and specific surface area of silica particles. The nature of particles was evaluated using X-ray diffraction, energy dispersive spectroscopy (EDS) and BET. The morphology of particles were determined by scanning electron microscopy (SEM) and transmission electron microscopy(TEM).

Abstract: In this work, high purity BaTiO3 (BT) nano-powders by a sol-gel process was prepared with Ba(NO3)2 and Ti(C4H9O)4 materials in order to acquire uniform size grains. The effects of the crystallinity, microstructure of BT nano-powders calcined at different temperatures and dielectric properties of the ceramics were investigated by XRD, SEM and impedance analyzer, respectively. Scanning electron microscopy and X-ray diffraction investigation revealed cubic plates and crystallite size. The results revealed that crystallite size and calcination temperature of BT and influence on the dielectric constant.

Abstract: This work describes the combination of photolithography and self-assembly methods for fabrication of 3D photonic crystals (PCs) with well-defined micron-scale line defects embedded in the PCs. Line defects with different dimensions, shapes, and compositions have been introduced into the 3D PCs by choosing different photoresists, masks, and template-directed assembly techniques. Infiltration of carbon using high-temperature chemical vapor deposition (CVD) technique showed that the fabrication procedure offers an ideal approach to functional 3D photonic devices from self-assembled photonic crystals.

Abstract: Iron oxide nanoparticles have been synthesized by laser-induced vapor-phase reaction. Mean diameter of the particles varied from approximate 4 nm to 40 nm and the crystalline phase was transited from γ-Fe2O3 to α-Fe2O3 with increasing operation temperature. The nanometer-sized α-Fe2O3 powders were used to fabricate a thick film based gas-sensitive sensor. The effects of the doped noble metals or carbonate and the calcination temperature on sensitivity of the sensor were studied. The results show that the α-Fe2O3 was doped with 3% noble metal or SrCO3 presents the best sensitivity to CO.

Abstract: Monodisperse silica particles containing available active C=C bonds were directly prepared by a simple two-step sol-gel method. In the first step the hydrolysis of vinyltrimethoxysilane (VTMS) was performed under acidic conditions in an aqueous solution. In the second step the condensation of the siloxane precursors progressed under basic conditions, resulting in production of silica nanoparticles containing available active C=C bonds. The products were characterized using SEM and FTIR.

Abstract: High ordered mesoporous carbon molecular sieves designated as CMK-3 and CMK-5 was synthesized using mesoporous silica SBA-15 as hard template, pre-polymerized furfuryl alcohol as a carbon souse by one-step impregnation. The effect of the furfuryl alcohol to silicas ratio have been investigated. XRD pattern, N2 sorption, FE-SEM, TEM, TG-DSC was used to characterize the property of the product. These results show that the CMK-3 and CMK-5 type mesoporous carbon can be controlled and facilely obtained.