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Authors: Hideo Kohno, Seiji Takeda
Abstract: This paper describes our recent achievements in fabricating various kinds of nanowires of silicon-based materials including beta iron-silicide, silicon carbide, and silicon germanium. Some of them can be grown directly at one-step process, while the others can be fabricated using nanowire templates. We discuss their structures, growth mechanisms, and properties based on electron microscopy observations.
Authors: Ji Cheng Zhou, Jian Wu Yan
Abstract: The nano Ni-Cr thin-film samples with different composition have been fabricated by a double-target magnetron co-sputtering equipment, through controlling the sputtering power, the substrate rotate speed, and the substrate temperature, The results showed that the grains sizes with polycrystalline microstructure were not greater than 10 nm. The crystal microstructure of Ni-Cr thin-films is Face Centered Cubic (FCC). The dominant texture in the Ni-Cr film was Ni (111) under this sputtering condition. The lattice parameters of Ni crystal and the inter-planar distances of Ni (111) increased by Cr solid-soluble in Ni crystal. The surface morphology of the thin-film samples is smooth and compact. The TCR (temperature coefficient of resistance) value of specimen 3 was 84~130 ppm/k, which show the specimen 3 was the most stable.
Authors: Hideto Yoshida, Tetsuya Uchiyama, Jun Kikkawa, Hideo Kohno, Seiji Takeda
Abstract: Single-walled carbon nanotubes (SWNTs) have been synthesized on silicon nanowires (SiNWs) by ethanol chemical vapor deposition (CVD) using Co catalysts nanoparticles. The surface SiOx layers assist the formation of catalyst nanoparticles on SiNWs by inhibiting the diffusion of Co to Si. Co-Si compounds have formed in SiNWs readily when the surface SiOx layers are very thin. Therefore, the yield of SWNTs is strongly influenced by the thickness of the surface SiOx layers of SiNWs.
Authors: Tsutomu Sakata, Katsunori Makihara, Hidenori Deki, Seiichiro Higashi, Seiichi Miyazaki
Abstract: We have studied uniform growth of crystalline Ge films on quartz plate from VHF (60MHz)-ICP of 10% GeH4 diluted with H2 in the temperature range from 150 to 350°C. By optimizing total gas flow rate, gas pressure, VHF power and antenna-substrate distance, the growth rate as high as 7.4nm/s was obtained at 150°C and increased gradually up to ~7.9nm/s at 350°C. The crystallinity, which was evaluated by Raman scattering measurements as an integrated intensity ratio of TO phonons in crystalline phase to those in disordered phase, reached a value as high as ~93 % at 350°C, but degraded down to 64% at 150°C as a result of the formation of a 60~70nm-thick amorphous incubation (A. I.) layer on quartz. By applying a two-step deposition method at 150°C, in which the GeH4 concentration was selected to be 0.6% for the crystalline nucleation in the first 10s deposition, being as thin as 10nm in thickness, and then changed to 10% GeH4 for the high rate growth, the crystallinity was improved to 78% with keeping an effective growth rate as high as 7.5nm/s, because of a significant increase in the growth rate after the crystalline nucleation.
Authors: Ryousuke Nishihara, Katsunori Makihara, Yoshihiro Kawaguchi, Mitsuhisa Ikeda, Hideki Murakami, Seiichiro Higashi, Seiichi Miyazaki
Abstract: We have formed high density nanodots of nickel silicide (NiSi) on ultrathin SiO2 and characterized their electronic charged states by using an AFM/Kelvin probe technique. Si quantum dots (Si-QDs) with an areal dot density of ~2.5x1011cm-2 were self-assembled on ~3.6nm-thick thermally-grown SiO2 by controlling the early stages of LPCVD using pure SiH4 gas. Subsequently, electron beam evaporation of Ni was carried out as thin as ~1.7nm in equivalent thickness at room temperature and followed by 300°C anneal for 5min in vacuum. XPS and AFM measurements confirm the formation of NiSi dots with an average dot height of ~8nm. After removal of Ni residue on SiO2 by a dilute HCl solution, bias conditions required for electron charging to NiSi dots were compared with those to pure Si-QDs dots and Ni dots. The surface potential changes stepwise with respect to the tip bias due to multistep electron injection and extraction of NiSi nanodots. In addition, it is confirmed that charge retention characteristics of NiSi dots are superior to those of Si-QDs with the almost same size.
Authors: Kazuhiro Ito, Yu Uchida, Sang Jin Lee, Susumu Tsukimoto, Yuhei Ikemoto, Koji Hirata, Toshiya Uemura, Masanori Murakami
Abstract: We investigated effect of reducing thickness of TiN buffer layers on growth of the smooth GaN layers. The sputtered TiN layers with thicknesses in the range of 2 to 100 nm were deposited on sapphire substrates. The sputtered TiN layers were exposed NH3 + H2 mixed gas atmosphere at about 1000°C to enrich nitrogen concentration of the layers. GaN layers were deposited on the nitrogen-enriched TiN layer using a MOCVD method. Average grain size of the nitrogen-enriched TiN layer was minimized at the thickness of 5 nm. In the initial stages of GaN growth, density of GaN hexagons grown on the 5nm-thick TiN layers was the highest. The 2μm-thick GaN layers grown on the 5nm-thick TiN layers exhibited the smoothest surface. Thus, the 5nm thickness is believed to be the best thickness for the smooth GaN growth on the sapphire/TiN substrates.
Authors: Dai Nishijima, Tatsuo Tabaru, Morito Akiyama
Abstract: Aluminum nitride (AlN) thin films formed on the heat-resistant alloy substrates were heated to 1100K. Cracking was observed in the AlN film formed on the stainless steel substrate (SUS430), while no crack was seen in that on the nickel-base superalloy substrate (IN750X). The electrical impedance measurements, X-ray diffraction analysis and finite element method calculation have been conducted to discuss the relationship between the cracking and the stress introduced into the AlN films. The AlN film cracking would be significantly affected by grain refinement of AlN.
Authors: Takayuki Ohba
Abstract: With the highest brilliance synchrotron radiation X-ray (SPring-8) and TEM observations, Cu oxides ranged 2-nm to 10-nm in thickness formed on sputtered Cu has been evaluated. For the plasma-assisted Cu oxide, weak Cu2O and/or CuO X-ray diffraction pattern is observed, while no diffraction pattern in native and thermally (170°C) grown oxides. Those native and thermal oxides show Cu2O coordination observed by XANES (X-ray Absorption Near Edge Structure) method. This suggests that Cu oxide formed at low temperatures consists of stoichiometric Cu2O in an amorphous structure. According to the Fowler-Nordheim (F-N) current emission model, the current emission taking place at Cu2O decreases with increasing of the oxide thickness and its mean barrier height (φB) in the MIM band structure. In case of current density at 106A/cm2 of 1V, it is estimated that the allowable thickness of Cu oxides is approximately 1.5-nm at 1 eV of barrier height.
Authors: Li Li, Fang Tao Zi
Abstract: Fluorocarbon polymer thin films on NiTi alloys possess extremely potential prospect. In this paper, the preparation of thin films on NiTi alloys by radio-frequency (RF) magnetron sputtering from polytetrafluoroethylene (PTFE) targets under argon is introduced. Sputtered fluorocarbon thin films on NiTi alloys are characterized by means of atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and their basic properties, especially structure and morphology, are revealed.
Authors: Yasuhiro Shigetoshi, Susumu Tsukimoto, Hidehisa Takeda, Kazuhiro Ito, Masanori Murakami
Abstract: The electrical and optical properties, and microstructures of 100 nm-thick Ga2O3 films fabricated on Al2O3(0001) substrates by a sputtering deposition were investigated. The partial pressure of oxygen was controlled and the substrate temperature was kept to be 500 °C during deposition. With increasing the oxygen partial pressure, the structures of the Ga2O3 films deposited on the substrates were observed to change from amorphous to crystalline (monoclinic β-type Ga2O3). The transmittance of the Ga2O3 films was measured to be more than 80 % at the visible and ultraviolet regions although the electrical resistivity was high. In order to obtain both low electrical resistivity and high transmittance at the ultraviolet regions, the addition of active dopant elements such as Sn into the Ga2O3 films would be required.

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