Solid State Phenomena Vols. 124-126

Abstract: Morphological evolution of Si nanowires (Si-NWs) grown on Si (001) substrates is explored. The Si-NWs are fabricated by nanoscale Au-Si island-catalyzed rapid thermal chemical vapor deposition. The Au-Si islands (10-50 nm in dia.) are formed by deposition of Au thin film (1.2-3.0 nm) at room temperature and followed by annealing at 700oC. The Si-NWs are grown by exposure them to a mixture of gasses of SiH4 and H2. We found a critical thickness of the Au film for Si-NW nucleation at a given growth condition. Also, we observed variation in the growth rate and the dimension of the NWs depending on the growth pressure and temperature. The resulting NWs are ~30-100nm in diameter and ~0.4-5.0μm in length. Most of the NWs were aligned along the <111> direction. The morphological and dimensional evolution of the Si-NWs is discussed in terms of kinetics (atomic diffusion mechanism) and energetics (surface and interface energies).

Abstract: Nano-sized silver particles are considered to apply a silver paste for electrode because of its high conductivity on sintering at low temperature. In this study, silver nanoparticles as seeds were prepared by chemical reduction method with capping agent. Silver particles were prepared using SDS (Sodium dodecyl sulfate) as a surfactant and silver nanoparticles as seeds and reacted with ascorbic acid as a reduction agent. The silver seeds with 10-20 nm in size with uniform distribution were formed and the size and shape of silver particles were strongly dependent on the concentration of surfactant.

Abstract: Silver-doped silica gel was prepared by the reaction of colloidal silica and AgNO3. In the synthetic process, aluminum ions promote the chemical durability of silver-doped silica gel with dramatically decreasing the elusion of silica ions at the aqueous solution. Especially, aluminum ions induce slow release silver ion of silver-doped silica gel over a long period of time. Also, antimicrobial effects evaluated using a shake flask method resulted in a disinfection ratio of Staphylococcus aureus(ATCC 6538) and Escherichia coli(ATCC 25922) of over 99.9%, indicating high anti-microbial properties.

Abstract: The crystallization of α-Fe2O3/α-Al2O3(0001) thin films has been studied using real-time synchrotron x-ray scattering and atomic force microscope. In the sputter-grown amorphous films of various thicknesses at room temperature, we find the coexistence of α-Fe2O3 and Fe3O4 interfacial crystallites (~50-Å-thick), well aligned to the α-Al2O3[0001] direction. The amorphous precursor is crystallized to the epitaxial α-Fe2O3 grains in three steps with annealing temperature; i) the growth of the well aligned α-Fe2O3 interfacial crystallites to approximately 200-Å-thick, together with the transformation of the Fe3O4 crystallites to the α-Fe2O3 crystallites (< 400°C), ii) the growth of the less aligned α-Fe2O3 grains on top of the well aligned grains (> 400°C), and iii) the nucleation of the different less aligned α-Fe2O3 grains directly on the α-Al2O3 substrate (> 600°C). The surface evolution of the amorphous precursor films after annealing is consistent with the microstructure evolution during the crystallization.

Abstract: The optimum values of the porosity, pore size and transmittance of the coating layer were investigated to give the lower thermal conductivity of the smart glazing. The porosity of the aerogel film is 90%, and the pores with 50micron size are uniformly distributed through the film. The transmittance and thermal conductivity of smart glazing with 500 μm thickness is at about 80 % in the visible range(380-780nm) and 0.15 W/(m.K) respectively.

Abstract: Nanoparticles of TiC and TiCN were synthesized by a magnesium thermal reduction process. The process was performed in the sequence of (1) the transfer of TiCl4+C2Cl4 solutions into a liquefied magnesium protected with Ar, (2) the magnesium reduction of metal chlorides, (3) the formation of a titanium carbide by the reaction of Ti and C atoms released by the magnesium reduction, and finally (4) the vacuum separation of the residual liquid Mg and MgCl2. Titanium carbonitride could be synthesized by maintaining the reaction chamber in nitrogen atmosphere. The average particle size of both TiC and TiCN synthesized was about 80 nm each. The composition of the TiC nanoparticles was approximately TiC0.95 with 0.9 wt % free carbon whereas that of the TiCN nanoparticles was TiC0.46~0.53N0.46~0.51 with 0.1 wt % free carbon.

Abstract: Cadmium selenide(CdSe) nanoparticles were prepared in the aqueous solution containing isopropyl alcohol by the ultrasonic irradiation at room temperature. The cadmium chloride (CdCl2) and sodium selenosulfate (Na2SeSO3) were used as the cadmium and selenium source, respectively. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), UV-Vis absorption spectra and PL spectra were used to characterize the CdSe nanoparticles. XRD analysis revealed the formation of cubic structure CdSe. TEM images showed aggregated CdSe nanoparticles with the size of nanometer scale. Average size of CdSe nanoparticles were about 3.9, 5.0 and 5.1nm with sonication time of 6, 30 and 40 minutes, respectively. The surface emission became less intensive and shifted to red with increasing irradiation time. This paper presents the effects of ultrasonic on the formation of CdSe nanoparticles and its characteristics.

Abstract: As-received multilayered Co/Cu nanowire arrays were examined by TEM, which were synthesized by pulsed DC electrodeposition using anodized aluminum oxide (AAO) templates. The multilayered Co/Cu nanowire exhibited magnetism in the perpendicular direction to the long wire axis. These nanowire can be applied to sensor array, magnetic bead(biocompatible), MRI contrast enhancing agent, ferro-fluid. Although the characterization of the multilayered Co/Cu nanowire using XRD and VSM and microstructural analysis using TEM on the bare nanowires extracted from AAO templates have been reported, interface analysis between Co and Cu phase or HREM analysis has not been reported in detail. We have prepared TEM specimen with large thin area which was appropriate for the interface analysis between Co and Cu layer without removing AAO templates using tripod polishing method. Tripod polishing proved very efficient to secure the large observable area during TEM session since the polishing angle can be precisely controlled, regardless of the mechanical strength differences in constituents. Thus we could observe not only the interface between Co and Cu layer but also the interface between the metallic layers and AAO templates. Microstructure, composition, and the concentration variation of each Co and Cu layer and the interfaces were analyzed with TEM and STEM.

Abstract: We report the synthesis of carbon nanotubes (CNTs) from ethanol by a chemical vapor deposition (CVD) method. Ethanol used as carbon source is atomized by an ultrasonic evaporator at room temperature, and is injected into a CVD furnace through a nozzle installed inside the furnace. The SEM and TEM analysis shows that the product contained CNTs as major constituents with some impurities. The radial breathing mode (RBM) of Raman spectrum reveals that the SWNTs are included in the product. The average diameter of the MWNTs is about 30nm and that of the SWNTs is less than 2nm.