[show abstract][hide abstract] ABSTRACT: Si dissolution into Ge melt, solute transport in the Si-Ge solution and crystal growth of SiGe alloys were in-situ observed by X-ray penetration method. The rectangular shaped sandwich sample of Si (seed)/Ge/Si (feed) was used for the experiment. X-ray intensities penetrated through the sample, which was heated up to the growth temperature of 1,200 °C, were recorded by rectangular shaped CdTe line sensor as a function of time and temperature. The experimental results demonstrated that the dissolution of Si seed was larger compared to Si feed crystal although Si feed temperature was relatively higher than that of seed. Crystal growth of SiGe was observed at the feed interface as the growth interface was observed clearly by an abrupt change of penetrated X-ray intensity near the growth interface. Since the crystal grew with Si rich composition (at high temperature 1,200 °C), solution becomes Ge richer which causes penetrated X-ray intensity variation at the growth interface. The growth mechanism for the observed SiGe growth process was discussed based on the penetrated X-ray intensity profile and a growth model. The composition of the grown sample was measured by FE-EPMA analysis.
Journal of Alloys and Compounds 12/2013; · 2.39 Impact Factor
[show abstract][hide abstract] ABSTRACT: Chromium disilicide (CrSi2) nanostructures were grown by the exposure of Si substrates to CrCl2 vapor at atmospheric pressure, and the growth condition dependence on the morphological and structural properties of CrSi2 was systemically investigated. The various structures of CrSi2, such as microrods, nanowire bundles along with microrods and dendritic nanowire structures, have been grown. It was found that the Si substrate temperature and the quantity of the CrCl2 source materials significantly affect the morphological and structural properties of the CrSi2 structures. The structural evolution of CrSi2 has been discussed on the basis of thermodynamic reactions, vapor deposition growth and dendritic growth phenomena. This growth process provides a simple and controllable method to grow novel nano-scaled structures of transition metal silicides for technological use.
Journal of Crystal Growth 02/2013; 365:11–18. · 1.55 Impact Factor
[show abstract][hide abstract] ABSTRACT: β-FeSi2 bulk crystals were grown by a molten salt method with Cu or Co addition. The effect of the Cu or Co addition on the structural, electrical and thermoelectric properties was investigated. A p-type semiconducting β-FeSi2 crystal was obtained without any impurity addition. On the other hand, n-type β-FeSi2 crystals were obtained by Co doping with 1.5–4 mol% addition. For the Cu addition, β-FeSi2 crystals with large diameter columnar domains were obtained, and an increased β-phase formation was observed. In addition, a slight decrease in the carrier density and a slight increase in the Hall mobility were observed, probably due to the elimination of crystalline defects. The structural and electrical modifications of the β-FeSi2 crystals by the impurity addition is discussed.
Journal of Crystal Growth 02/2012; 340(1):51–55. · 1.55 Impact Factor
[show abstract][hide abstract] ABSTRACT: MoSi2 and WSi2 layers were grown on Mo and W substrates using the molten salt method. In addition, the Mo- and W-silicide compacts with the addition of Ti were also synthesized using Mo and W powders as the source materials, respectively, then the structural and electrical properties of the silicides were investigated. It was found that Si atoms penetrate into the compacts during the molten salt process. Moreover, nano-sized h-MoSi2 and h-WSi2 with the addition of Ti were formed in the compacts. The electrical conductivity of the compact comprised of Mo(Ti)Si2 showed almost no temperature dependence. On the other hand, for the compact comprised of W(Ti)Si2, the temperature dependence of the electrical conductivity showed a semiconducting property with an activation energy of about 0.18 eV.
IOP Conference Series Materials Science and Engineering 06/2011; 18(14):142010.
[show abstract][hide abstract] ABSTRACT: Ca2Si powders have been synthesized by the thermal treatment of Mg2Si with NaI or Na2CO3 under Ca vapors, then sintered into compacts by sparking plasma sintering (SPS) technique. As a comparison, the compact was also sintered using Ca2Si with NaI powders by the SPS technique. The effect of Na addition on the structural, transport and thermoelectric properties of the Ca2Si compacts has been examined. All the samples show a p-type behavior in the measured temperature range. The Ca2Si with Na2CO3 by vapor phase growth shows a higher carrier concentration of 1.28×1018 cm−3 conductivity about 10 times higher than Ca2Si, and a power factor about 5 times higher than Ca2Si from 350K to 570K.
IOP Conference Series Materials Science and Engineering 06/2011; 18(14):142014.
[show abstract][hide abstract] ABSTRACT: Sr2SiO4 flower-like nanostructures were grown by thermal oxidation of SrSi2 powders with Ga droplets. The morphology and structure of the Sr2SiO4 flower-like nanostructures were investigated using transmission electron microscopy. The leaves of the Sr2SiO4 flower-like nanostructures became narrow towards the tips. Sr, Si and O were homogeneously concentrated on each leaf. In addition, the formation mechanism of the Sr2SiO4 flower-like nanostructures was discussed.
[show abstract][hide abstract] ABSTRACT: Single-phase orthorhombic Ca2Si sintered compacts were synthesized by the spark plasma sintering technique. The electronic structures and Seebeck coefficient of Ca2Si were calculated using the first-principles total-energy calculation program. It was found that the Ca2Si compact showed a p-type conductivity of ∼10−2 S/cm with an activation energy of 0.13 eV, and the experimental Seebeck coefficient is larger than 250 μV/K from 373 K to 573 K.
[show abstract][hide abstract] ABSTRACT: ZrO2/SiOx core/shell nanofibers with diameter ~50nm were synthesized by the thermal oxidation of ZrSi2 substrates with gallium. The crystalline ZrO2 cores were grown with amorphous SiOx shells. It is proposed that the growth of crystalline ZrO2 core was guided by the prior supersaturation of Zr species in the molten gallium film, whereas the amorphous SiOx shell could be attributed to the deposition of SiO vapor on the surface of ZrO2 core. In addition, the ZrO2/SiOx core/shell nanofibers show a wide visible photoluminescence (PL) emission at 480nm, which should originate from the SiOx shells.
Thin Solid Films 01/2011; 519(24):8538-8541. · 1.60 Impact Factor
[show abstract][hide abstract] ABSTRACT: The electrical and thermoelectric properties of group VI metal silicides, such as the Mo- and W-silicides as well as CrSi2, were investigated. The electronic band structures of the hexagonal- MoSi2, - WSi2 and CrSi2, were calculated using the first-principles total-energy calculation program in pseudopotential schemes with plane-wave basis functions, and their Seebeck coefficients were also calculated. In addition, the Mo- and W-silicides were synthesized using mechanical alloying followed by a spark plasma sintering technique, and their structural, electric and thermoelectric properties were examined.
[show abstract][hide abstract] ABSTRACT: Phase selection during Ca silicide formation was discussed using the chemical potential and the effective heat of formation (ΔH′) models. The compositional analyses of Ca silicides were experimentally carried out in detail for both the layered and powder growth process. Based on the calculation, the Ca2Si phase has the largest negative ΔH′ and is the first phase to form in the Ca–Si system. In addition, the total energy consideration consisting of the formation energy of each phase and interfacial energy between two adjoining phases is proposed to explain the experimental results of phase selection in the Ca silicide formation.
Journal of Alloys and Compounds 01/2011; 509(13):4583-4587. · 2.39 Impact Factor
[show abstract][hide abstract] ABSTRACT: Alpha-Fe2O3 nanowires and nanobelts were grown by the thermal oxidation of iron substrates with or without gallium droplets in the air. The nanowires and nanobelts show a bicrystal structure with the growth direction uniformly along . The morphological and structural properties of the as-grown alpha-Fe2O3 nanostructures are described and the growth condition dependence of the alpha-Fe2O3 nanostructures is shown. The transformation from nanowires to nanobelts occurs with the increase of growth temperature and addition of gallium. In addition, the growth evolution is investigated with reference to the Fe surface diffusion and supersaturation.
Journal of Nanoscience and Nanotechnology 11/2010; 10(11):7795-9. · 1.15 Impact Factor
[show abstract][hide abstract] ABSTRACT: In this study, we showed a variety of nanowire and nanobelt based oxides, including ZnO, -Fe2O3 and -Ga2O3, grown by the thermal oxidation with gallium in air. These results revealed the availability of such a simple growth method for the oxide nanostructure growth. In addition, the effect of gallium on the nanostructure growth (e.g., ZnO nanowires & nanobelts) and morphology transformation (e.g., -Fe2O3 nanowires & nanobelts) was demonstrated, which provided the possibility of the selective growth of oxide nanostructures. Various other oxide nanostructures are expected when considering the anisotropic surface energy and nonhomogeneous supersaturation conditions, as well as the growth condition dependence of the selective growth.