Advanced Materials Research Vols. 11-12

Abstract: The growth of 3C-SiC on thermal oxide layer of Si (SiO2) was investigated by hot-mesh (HM) chemical vapor deposition (CVD), which utilizes hot tungsten (W) wires of a mesh structure as a catalyzer. The SiC films were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and cross sectional transmission electron microscopy (TEM). From the XRD spectra of SiC films grown on SiO2 layer, (100) oriented SiC films were grown at the substrate temperatures of 750-800°C and the mesh temperature of 1600°C, while polycrystalline SiC films were grown at the substrate temperature above 900°C. From the data of FT-IR, TEM and the growth rate, the growth characteristics of SiC crystal by HMCVD were discussed.

Abstract: Gallium nitride (GaN) films were grown on SiC/Si(111) substrates by hot-mesh chemical vapor deposition (CVD) using trimethylgallium (TMG) and ammonia (NH3). A SiC buffer layer was formed by carbonization on the Si(111) substrates using propane (C3H8). GaN epitaxial films were grown on the SiC layer by the reaction between NHx radicals generated on a tungsten hot-mesh surface and TMG molecules. From the X-ray diffraction pattern, the GaN epitaxial films grown by the two- or three-step growth technique at the substrate temperatures of 600°C and 800°C to 1000°C and the hot-mesh temperature of 1200°C showed good crystallinity. Photoluminescence spectra of GaN films grown by the three step growth technique showed a strong near-band-edge emission and a weak yellow luminescence.

Abstract: The heteroepitaxial growth of 3C-SiC films on Si(100) substrates by the hot-mesh chemical vapor deposition (HM-CVD) method using monomethylsilane as a source gas was investigated. From the results of X-ray diffraction spectra, 3C-SiC crystal was epitaxially grown on Si substrates at substrate temperatures above 750°C. The SiC/Si interface was observed by cross-sectional scanning electron microscopy, and was confirmed to be void-free and smooth. The density of hydrogen radicals supplied to the substrate surface during the growth was also estimated measuring the optical absorbance change of tungsten phosphate glass plates. From the dependence of the growth rate on substrate temperature, the mechanism of SiC film growth by HM-CVD was considered.

Abstract: We developed a new zinc oxide (ZnO) crystal growth method using Au combined with electric current heating. Au paste was placed on a ZnO ceramic bar. When a certain current flowed through the bar, the paste melted on the bar. Then crystals grew on the molten Au surface immediately. The shape of the crystals depended on the atmosphere during the growth. The whiskers with spherical top and the crystals consisting of a hexangular pyramidal base and needle head were grown on Au in air and Ar atmosphere, respectively. From cathodoluminescence at room temperature, the weak ultraviolet (UV) emission at approximately 3.2 eV and the strong visible emission at approximately 2.3 eV were observed from the whisker grown in air. The UV emission at approximately 3.3 eV dominated a spectrum from the pyramidal crystal grown in Ar atmosphere.

Abstract: The inorganic and organic hybrid compound, [O=VPd(2-Pyd-)4]n (2-Pyd- = 2-pyridonate) (1), was synthesized by assembling its monomer units in the organic solution. X-ray absorption spectroscopic (XAFS) studies indicated that oxidation states of the vanadium and palladium ions in 1 were +IV and +II, and the distance between them was estimated to be 2.698-2.700 Å. Scanning electron microscope (SEM) observation revealed that the compound 1 shapes in long columnar crystals with micrometer-sized cross section. EXAFS and IR studies suggested that the O=V oxygen atom interacted to the central palladium ion in the neighboring monomer unit, forming the inorganic infinite chain structure, -(O=V-Pd)n-, in the columnar crystals of 1.

Abstract: Two new bipyridine derivative ligands with an extended π electron system and a triple hydrogen bond group, 2,4-diaminopyrimido[5,6-b]dipyrido[2,3-f:2’,3’-h]quinoxaline (DAPQ) and 2,4(1H,3H)-pyrimidinedion[5,6-b]dipyrido[2,3-f:2’3’-h]quinoxaline (PDPQ), were synthesized in order to construct high-performance Ru(II) complexes. The two Ru(II) complexes composed of dapq or pdpq and two 2,2’-bipyridine (BPY) ligands showed characteristic luminescent spectra with a peak maximum at ca. 610 nm. The octahedral Ru(II) complexes with a D-A-D (D: proton donor; A: proton acceptor) type triple hydrogen bond indicated intense luminescence in comparison with the corresponding Ru(II) complex composed of three BPY ligands. When the triple hydrogen bond was formed with a Co(III) complex with the D-A-D type hydrogen bonding group, the luminescence was quenched. This result was explained in terms of an energy transfer from an excited Ru(II) complex to the Co(III) complex.

Abstract: Nickel(II) phthalocyanine complexes encapsulated in X-type Zeolite were constructed by the ‘Ship-in-bottle’ synthesis, whose characterizations were performed by fluorescent X-ray, UV-vis, reflectance, and ESR spectroscopic methods. UV-vis and Reflectance spectra of NiPc-Na+-X suggested that the Pc ring was synthesized. Solid state ESR spectrum of NiPc-Na+-X gave characteristic pattern for organic radical species. Catalytic oxidation reactivity of the NiPc-Na+-X in homogeneous reaction have been studied for organic substrate in the presence of H2O2.

Abstract: A new diferrous complex with asymmetric coordination sites, [Fe2(μ-OBz)(L)](ClO4)2 (1) (L = N,N-bis(6-methyl-2-pyridylmethyl)-N’,N’-bis(6-pivalamido-2-pyridylmethyl)-1,3-diaminopropan- 2-ol), was synthesized, which was immobilized in the internal surface of mesoporous silica (FSM-16) to construct a functional material (1A). The reaction of 1 with O2 in acetone at –50°C generated a peroxo complex 2 [λmax = 589 nm (ε = 2200 M-1 cm-1), ν16O-16O = 890 and 908 cm-1 (ν18O-18O = 852 cm-1)]. The μ-peroxo complex 2 was decomposed by bubbling of Ar gas without releasing O2, but the reaction of 1A with O2 at ambient temperature also formed a peroxo complex (2A) without decomposition. The reflectance spectrum of 2A showed a band assignable to the LMCT band from peroxo to a Fe(III) ion at 588 nm. Compound 2A is very stable, whose half-life time is 45 min, in contrast to a short life of 2 (310 sec). 2A released dioxygen by heating up to 75°C in vacuo, which was regenerated by bubbling of dioxygen at ambient temperature.

Abstract: Biomorphic SiO2/C and SiC/C composites containing SiO2 nanorods and SiC nanowires, respectively, with natural wood structure maintained in the final products were fabricated by a simple and low cost method. Freshly cut Luk bamboo was used as the starting material and was converted to charcoal bio-templates by pyrolysis. Infiltration of Si-containing metal-organic solution was then conducted by soaking the bio-templates into the solution for a few days. Finally, by high temperature annealing, biomorphic composites were produced. It was found that C, SiC, and SiO2 micron-sized spheres or nanorods, depending on the annealing duration, were present in the samples annealed at 1200°C; whereas only C, and SiC nanowires were present in the samples annealed at 1400°C.

Abstract: A new route has been developed to prepare polyaniline (PANI)/ layered double hydroxides (LDHs) nanocomposites through in situ chemical oxidative polymerization of metanilic acid (m-NH2C6H4SO3H) intercalated in MgAl LDH under nitrogen atmosphere by using the pre-intercalated nitrate as the oxidizing agent. The whole process involves the synthesis of the precursor LDHs [Mg2Al (OH)6](NO3)·nH2O, the intercalation of the monomer metanilic acid into LDH and its in situ polymerization between the layers by thermal treatment under nitrogen atmosphere. The interlayer polymerization was monitored by thermogravimetry (TG)-differential thermal analysis (DTA) - mass spectrometry (MS), UV-vis spectroscopy and in situ high temperature X-ray diffraction (HT-XRD). UV-vis spectroscopy give strong evidence on the polymerization of the intercalated metanilic acid, with the increase of the interlayer distance and broadening of the diffraction peaks. It has been found by the in situ technologies that the co-intercalated nitrate anions act as the oxidizing agent which participate in the polymerization of the interlayer monomers under nitrogen atmosphere by heating from 300 oC to 350 oC.