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Applied Surface Science (v.254, #23)

Cooling rate effects on structure and thermodynamics of amorphous nanoparticles by Vo Van Hoang; T. Odagaki; M. Engel (pp. 7531-7534).

Cooling rate effects on structure and thermodynamics of amorphous nanoparticles were studied in a spherical model using Molecular Dynamics (MD) method. The good equilibrium melts are cooling down by three different cooling rates in order to observe the cooling rate effects. We find that cooling rate effects on thermodynamic quantities such as potential energy and surface energy are more pronounced than those for static quantities. Microstructure of amorphous nanoparticles is analyzed via radial distribution function (RDF) and coordination number distributions. Relatively weak cooling rate effects on such quantities are found. Microstructure of surface and core of amorphous nanoparticles are analyzed.

Keywords: PACS; 61.46.−w; 78.55.Qr; 61.43.BnCooling rate effects; Amorphous nanoparticles; Surface energy; Glass transition

The adsorption-induced thermal step-bunching on the hexagonal lattice system by Noriko Akutsu; Yoshinari Kakii (pp. 7535-7538).

We present restricted solid-on-solid model coupled with Ising system (RSOS-I model) on the hexagonal system. Without long-range interaction such as elastic interaction, the adsorption-induced thermal step-bunching is obtained by the Monte Carlo calculation on the hexagonal RSOS-I model.

Keywords: PACS; 68.35.Md; 05.70.Np; 05.50.+q; 68.35.; −; pStep-bunching; Self-organization; Adsorption; Hexagonal system; Restricted solid-on-solid model

Confocal Raman spectroscopic mapping studies on a single CuO nanowire by M.H. Chou; S.B. Liu; C.Y. Huang; S.Y. Wu; C.-L. Cheng (pp. 7539-7543).

In this study we are able, using a copper grid substrate, to successfully grow separate nanowires with a high level of crystallinity, for a length of up to 10μm. They were synthesized under various temperatures. We compare and contrast three types of geometries (micron-, nano-scale, and tip-like single CuO nanowires), to identify their potential for monitoring the size effects of quantum confinements. The confocal Raman spectrometry results confirm the expected outcome, that reducing of the diameter of a cylindrical cross-section of a single nanowire results in Raman frequency downshifts. The results can be explained by the bond polarizability model. The applicability of investigating the size effects of the quantum confinement of the tip-like geometry of a single nanowire without any preparation for different sizes of nanoparticles is possible because the detection is relatively straightforward and the reproduced Raman signals can be observed.

Keywords: PACS; 78.30.−j; 81.07.Bc; 87.64.TtConfocal Raman spectroscopy; Cupric oxide; Nanowire

Effect of Ge surface termination on oxidation behavior by Younghwan Lee; Kibyung Park; Yong Soo Cho; Sangwoo Lim (pp. 7544-7548).

Sulfur-termination was formed on the Ge(100) surface using (NH₄)₂S solution. Formation of Ge–S and the oxidation of the S-terminated Ge surface were monitored with multiple internal reflection Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. In the 0.5, 5, or 20% (NH₄)₂S solution, H-termination on the Ge(100) surface was substituted with S-termination in 1min. When the S-terminated Ge(100) surface was exposed in air ambient, the oxidation was retarded for about 3600min. The preservation time of the oxide layer up to one monolayer of S-terminated Ge(100) surface was about 120 times longer than for the H-terminated Ge(100) surface. However, the oxidation of S-terminated Ge(100) surface drastically increased after the threshold time. There was no significant difference in threshold time between S-terminations formed in 0.5, 5, and 20% (NH₄)₂S solutions. With the surface oxidation, desorption of S on the Ge surface was observed. The desorption behavior of sulfur on the S-terminated Ge(100) surface was independent of the concentration of the (NH₄)₂S solution that forms S-termination. Non-ideal S-termination on Ge surfaces may be related to drastic oxidation of the Ge surface. Finally, with the desulfurization on the S-terminated Ge(100) surface, oxide growth is accelerated.

Keywords: PACS; 61.72.uf; 66.70.Df; 68.35.bg; 68.37.−dGermanium; Surface; Termination; Oxidation

Circular dichroism of forward focusing peaks and diffraction rings in 2π steradian Si 2p photoelectron pattern by Kanako Inaji; Fumihiko Matsui; Yukako Kato; Chikako Sakai; Takashi Narikawa; Tomohiro Matsushita; Fang Zhun Guo; Hiroshi Daimon (pp. 7549-7552).

2π steradian Si 2p photoelectron pattern from Si(001) surface was measured. The circular dichroism of rotational shift around the incident-light axis was observed. Shifts for the forward focusing peaks in{111} and{011} directions were inversely proportional to the distance between the emitter atom and neighboring atoms in{111} and{011} directions, respectively. These shifts correspond to the parallax in stereograph of the atomic arrangements. On the other hand, such rotational shifts were not observed in{112} directions due to the first order diffraction rings around{110} directions. A gross feature of Si 2p photoelectron pattern can be explained by forward focusing peaks and first order diffraction rings around them.

Keywords: PACS; 61.05.js; 68.35.bg; 79.60; .; −; iPhotoelectron diffraction; Surface structure; Silicon; Circular dichroism; Forward focusing peak; Stereoatomscope

Characterization of PbS with different morphologies produced using a cyclic microwave radiation by Anukorn Phuruangrat; Titipun Thongtem; Somchai Thongtem (pp. 7553-7558).

PbS was produced from different lead (Pb(CH₃COO)₂·H₂O, PbCl₂·2.5H₂O, Pb(NO₃)₂) and sulfur (CH₃CSNH₂, CH₅N₃S, NH₂CSNH₂) sources in propylene glycol using a cyclic microwave radiation at different powers and prolonged times. PbS (cubic) was detected using X-ray diffraction (XRD) and selected area electron diffraction (SAED) techniques. The interpreted and simulated patterns are in good accord. Raman spectrometer revealed the presence of vibrations at 138, 273 and 439cm⁻¹. Different morphologies (nano-sized particles, hexapods, cubes, ferns and magic squares) were characterized using a scanning electron microscope (SEM) and a transmission electron microscope (TEM). The product morphologies were influenced by the starting agents, microwave powers and prolonged times.

Keywords: PACS; 81.07.BcCyclic microwave radiation; PbS; Nano-sized particles; Hexapods; Cubes; Ferns; Magic squares

Effects of surface roughness on the electrical characteristics of ZnO nanowire field effect transistors by Woong-Ki Hong; Sunghoon Song; Dae-Kue Hwang; Soon-Shin Kwon; Gunho Jo; Seong-Ju Park; Takhee Lee (pp. 7559-7564).

We have systematically investigated the effects of surface roughness on the electrical characteristics of ZnO nanowire field effect transistors (FETs) before and after passivation by poly (methyl metahacrylate) (PMMA), a polymer-insulating layer. To control the surface morphology of ZnO nanowires, ZnO nanowires were grown by the vapor transport method on two different substrates, namely, an Au-catalyzed sapphire and an Au-catalyzed ZnO film/sapphire. ZnO nanowires grown on the Au-catalyzed sapphire substrate had smooth surfaces, whereas those grown on the Au-catalyzed ZnO film had rough surfaces. Electrical characteristics such as the threshold voltage shift and transconductance before and after passivation were strongly affected by the surface morphology of ZnO nanowires.

Keywords: PACS; 62.23.Hj; 73.63.−b; 81.07.−b; 85.35.−pSurface roughness; Passivation; ZnO; Nanowire; Field effect transistor

Influence of initial surface reconstruction on the interface structure of HfO₂/GaAs by Tetsuji Yasuda; Noriyuki Miyata; Akihiro Ohtake (pp. 7565-7568).

We show that the bonding structures and electrical properties of the HfO₂/GaAs interface can be controlled by a choice of the reconstruction on the initial GaAs surface. Electron-beam evaporation of HfO₂ onto the c(4×4) surface yielded As–O bonds at the interface, while Ga–O bonds were dominant at the interfaces formed on the (2×4) and (4×6) surfaces. Influences of the initial surface reconstruction on the interface structure persisted even after annealing at 673K. Electrical characterization of Ir/HfO₂/GaAs capacitors indicated that the interfacial As–O bonds cause weak Fermi level pinning. It was also suggested that the interfaces dominated by the Ga–O bonds have trapping states in the upper half of the GaAs bandgap.

Keywords: PACS; 68.55.aj; 73.40.Qv; 77.55.+f; 78.68.+m; 81.05.Ea; 81.15.Ef; 85.30.TvHigh-k dielectrics; III–V semiconductor; HfO; ₂; GaAs; MOS interface; XPS; RDS

Spherical aberration corrected STEM studies of Ge nanodots grown on Si(001) surfaces with an ultrathin SiO₂ coverage by N. Tanaka; S.-P. Cho; A.A. Shklyaev; J. Yamasaki; E. Okunishi; M. Ichikawa (pp. 7569-7572).

Germanium (Ge) nanodots of about 7nm size and 2×10¹²cm⁻² density were formed on slightly oxidized silicon surfaces. The spherical aberration corrected scanning transmission electron microscopy (Cs-corrected STEM) revealed clearly the size, aspect ratio and interface structures among the nanodots, oxide layers and silicon substrates. In particular, a Ge-rich thin layer underneath SiO₂ layers was found for the first time in these kinds of samples. The elemental distribution through the interface was analyzed by EELS and EDX in the Cs-corrected STEM. The high-resolution Cs-corrected annular dark field (ADF)-STEM image shows clearly the existence of a Ge-rich crystalline layer and its geometry against the oxide layer from the Z-contrast image. A new growth model of the Ge nanodots on slightly oxidized silicon surfaces was proposed.

Keywords: Ge nanodot; Spherical aberration correction; ADF-STEM; Slightly oxidized silicon; Interface structure

Stability of the tunneling current across Si nanochain network by Hideo Kohno; Seiji Takeda (pp. 7573-7575).

The stability of the current across Si nanochain network is investigated using a micromanipulator in a scanning electron microscope system. We confirm that the current is dominated by the tunneling of electrons between Si nanoparticles. We observe large current fluctuations at a high bias voltage, while the current is stable at a relatively low bias voltage. The origin of the fluctuation is discussed in terms of percolation.

Keywords: PACS; 73.63.Bd; 68.37.Hk; 05.40.Fb; 05.70.JkSi nanochain; Current; Fluctuation; Percolation

Two-dimensional structures of pyrimido[5,4- d]pyrimidine derivatives at solid/liquid interface by Yoshihiro Kikkawa; Kazuhiro Taguchi; Seiji Tsuzuki; Emiko Koyama; Hideo Tokuhisa; Masatoshi Kanesato (pp. 7576-7580).

Two-dimensional structures of pyrimido[5,4- d]pyrimidine derivatives (PD) were studied by scanning tunneling microscopy (STM) at solid/liquid interface. In order to tune the intervals of functional unit (hydrogen bonding site) in the molecule, thePD with different numbers and length of alkyl chain were designed and synthesized. STM observation at highly oriented pyrolytic graphite (HOPG)/1-phenyloctane interface revealed that thePD with four alkyl chains formed a columnar structure, and the alkyl chains were not interdigitated. By contrast, thePD with two alkyl chains formed similar columnar structure, whereas the alkyl chains were interdigitated. These structural features of thePD indicates that the intervals of the functional unit, i.e., hydrogen bonding sites in thePD can be controlled by changing not only the length but also the number of alkyl chains.

Keywords: PACS; 68.37.Ef; 68.08.De; 81.07.Nb; 81.16.DnScanning tunneling microscopy (STM); Two-dimensional structure; Pyrimido[5,4-; d; ]pyrimidine; Solid–liquid interfaces; Highly oriented pyrolytic graphite (HOPG)

Characterization of MeWO₄ (Me=Ba, Sr and Ca) nanocrystallines prepared by sonochemical method by Titipun Thongtem; Anukorn Phuruangrat; Somchai Thongtem (pp. 7581-7585).

Metal tungstates (MeWO₄, Me=Ba, Sr and Ca) were successfully prepared using the corresponding Me(NO₃)₂·2H₂O and Na₂WO₄·2H₂O in ethylene glycol by the 5h sonochemical process. The tungstate phases with scheelite structure were detected with X-ray diffraction (XRD) and selected area electron diffraction (SAED). Their calculated lattice parameters are in accord with those of the JCPDS cards. Transmission electron microscopy (TEM) revealed the presence of nanoparticles composing the products. Their average sizes are 42.0±10.4, 18.5±5.1 and 13.1±3.3nm for Me=Ba, Sr and Ca, respectively. Interplanar spaces of the crystals were also characterized with high-resolution TEM (HRTEM). Their crystallographic planes are aligned in systematic array. Six different vibration wavenumbers were detected using Raman spectrometer and are specified as ν₁(A_g), ν₃(B_g), ν₃(E_g), ν₄(B_g), ν₂(A_g) and free rotation. Fourier transform infrared (FTIR) spectra provided the evidence of scheelite structure with W–O anti-symmetric stretching vibration of [WO₄]²⁻ tetrahedrons at 786–883cm⁻¹. Photoluminescence emission of the products was detected over the range of 384–416nm.

Keywords: PACS; 81.16.BeSonochemical method; BaWO; ₄; SrWO; ₄; CaWO; ₄; Nanocrystallines

Environmental transmission electron microscopy observations of the growth of carbon nanotubes under nanotube–nanotube and nanotube–substrate interactions by Hideto Yoshida; Tetsuya Uchiyama; Hideo Kohno; Seiji Takeda (pp. 7586-7590).

The growth process of carbon nanotubes (CNTs) under CNT–CNT and CNT–substrate interactions has been observed directly by environmental transmission electron microscopy. Even a free standing CNT occasionally swings during the growth until it touches the substrate. In addition, we show that the growth direction of CNTs changes due to the interaction between CNTs.

Keywords: PACS; 81.07.De; 68.37.Lp; 81.15.GhCarbon nanotubes; Environmental transmission electron microscopy; Chemical vapor deposition

Radial breathing modes of single-walled carbon nanotubes in resonance Raman spectra at high temperature and their chiral index assignment by Takashi Uchida; Masaya Tazawa; Hiroshi Sakai; Akira Yamazaki; Yoshihiro Kobayashi (pp. 7591-7595).

Radial breathing modes (RBMs) in resonance Raman spectra from single-walled carbon nanotubes (SWCNTs) on a SiO₂/Si (001) substrate are studied between 25 and 720°C. A change in the relative intensity of each RBM peak with temperature is observed, which originates from the temperature dependence of the resonance condition of nanotubes. For 25°C, each RBM peak is reasonably assigned on the basis of data in the literature [J. Maultzsch, H. Telg, S. Reich, F. Hennrich, C. Thomsen, Phys. Rev. B 72 (2005) 205438]. By taking into account the temperature-dependent behavior of the relative intensity of the RBM peaks, each RBM peak is successfully assigned even for 720°C. It is found that most of the observed RBM peaks for a laser excitation energy of E_exc=1.96eV are from chiral SWCNTs. These results make it possible to discuss further details of the chirality-dependent growth behavior observed for in situ Raman spectroscopy.

Keywords: PACS; 61.46.Fg; 78.30.NaSingle-walled carbon nanotubes; Raman spectroscopy; Radial breathing mode

Two-dimensional emission patterns of secondary electrons from graphene layers formed on SiC(0001) by H. Hibino; H. Kageshima; F.-Z. Guo; F. Maeda; M. Kotsugi; Y. Watanabe (pp. 7596-7599).

We used spectroscopic photoemission and low-energy electron microscopy to measure two-dimensional (2D) emission patterns of secondary electrons (SEs) emitted from graphene layers formed on SiC(0001). The 2D SE patterns measured at the SE energies of 0–50eV show energy-dependent intensity distributions in the 6-fold symmetry. The SE patterns exhibit features ascribed to energy band structures of 2D free electrons, which would prove that electrons are partially confined in thin graphene layers even above the vacuum level.

Keywords: Graphene; Silicon carbide; Secondary electron; Spectroscopic photoemission and low-energy electron microscopy

Contact and phonon scattering effects on quantum transport properties of carbon-nanotube field-effect transistors by Hiroyuki Ishii; Nobuhiko Kobayashi; Kenji Hirose (pp. 7600-7603).

We investigated the phonon scattering effects on the transport properties of carbon nanotube devices with micron-order lengths at room temperature, using the time-dependent wave-packet approach based on the Kubo formula within a tight-binding approximation. We studied the scattering effects of both the longitudinal acoustic and the optical phonons on the transport properties. The conductance of semiconducting nanotubes is decreased by the acoustic phonon, instead of the optical phonon. Furthermore, we clarified how the electron mobilities of the devices are affected by the acoustic phonon.

Keywords: PACS; 72.10.; −; d; 73.23; −; b; 73.63.FgQuantum transport; Carbon nanotubes; Time-dependent approach

Preparation of nano-sized platinum metal catalyst using photo-assisted deposition method on mesoporous silica including single-site photocatalyst by Sayoko Shironita; Kohsuke Mori; Toshiaki Shimizu; Tetsutaro Ohmichi; Naoki Mimura; Hiromi Yamashita (pp. 7604-7607).

Pt particles in a uniform dispersion were successfully synthesized on single-site photocatalyst (Ti-containing mesoporous silica (Ti-HMS)) under UV-light irradiation by a photo-assisted deposition (PAD) method. Using an aqueous solution of H₂PtCl₆ as a precursor, the nano-sized Pt metal particles were deposited directly on the photo-excited tetrahedrally coordinated titanium oxide moieties within the framework of mesoporous silica (PAD-Pt/Ti-HMS). The Pt catalysts were characterized by means of XRD, Pt L_III-edge XAFS, CO adsorption, and TEM analysis. It was demonstrated that Pt particles had mean diameter of 4nm in a narrow size distribution. Meanwhile, Pt particles loaded by a conventional impregnation method (imp-Pt/Ti-HMS) showed a wide size distribution ranging from 2 to 30nm. The PAD-Pt/Ti-HMS catalyst was more active in the CO oxidation than the conventional impregnated imp-Pt/Ti-HMS catalyst. It is suggested that the PAD method using single-site photocatalyst is a useful and unique technique to prepare fine and uniform Pt nanoparticles.

Keywords: Single-site photocatalyst; Platinum nanoparticle; Photo-deposition; CO oxidation

Theoretical investigation of ethylene/1-butene copolymerization process using constrained geometry catalyst (CpSiH₂NH)-Ti-Cl₂ by Hema Malani; Shigekazu Hayashi; Huifeng Zhong; Riadh Sahnoun; Hideyuki Tsuboi; Michihisa Koyama; Nozomu Hatakeyama; Akira Endou; Hiromitsu Takaba; Momoji Kubo; Carlos A. Del Carpio; Akira Miyamoto (pp. 7608-7611).

The ethylene/1-butene copolymerization using constrained geometry catalyst CpSiH₂-NH-TiCl₂ (CGC) was investigated by the density functional theory and molecular dynamics. Structures and energetics of reactants, π-complexes, transition states, and products during insertion of ethylene and 1-butene monomers into the catalytic reactive site of the CGC were investigated by the density functional theory (DFT) using the software Dmol³, while dynamics of atoms during copolymerization process was investigated by classical molecular dynamics (MD) using the New-Ryudo-CR program. The calculated results were compared with the available experimental and theoretical ones. It was found that the ethylene insertion into Ti-Me active species is energetically more favorable than the butene one and the 2,1-butene insertion is more favorable than 1,2-butene one. Once the initial ethylene insertion has taken place, the further ethylene insertion occurring with a less energy barrier, in good agreement with experimental findings.

Keywords: PACS; 82.35.−x; 71.15.Mb; 71.15.PdPolymerization; Density functional theory; Molecular dynamics

Synthesis and utilization of Mg/Al hydrotalcite for removing dissolved humic acid by Sri Juari Santosa; Eko Sri Kunarti; Karmanto (pp. 7612-7617).

It has been synthesized Mg/Al layered double hydroxide anionic clay (Mg/Al hydrotalcite) through direct precipitation by adding 0.5M NaOH solution into a mixed solution containing Mg(NO₃)₂ and Al(NO₃)₃ with molar ratio of 0.1:0.05 until the medium acidity reached pH 10.1. The synthesized Mg/Al hydrotalcite was then utilized to remove dissolved humic acid in aqueous medium. The humic acid was isolated from peat soil taken in Gambut District, South Kalimantan, Indonesia using the recommended procedure of IHSS (International Humic Substances Society). The removal of humic acid was mostly occurred through simple sorption process without accompanied by significant intercalation. The sorption was optimum at pH 9.0, with the first order rate constant, capacity and energy of sorption were 5.50×10⁻³min⁻¹, 0.12mmolg⁻¹ (69mgg⁻¹), and 28.32kJmol⁻¹, respectively.

Keywords: PACS; 61.10.Nz; 61.18.−j; 61.25.HqHumic acid; Removal; Mg/Al hydrotalcite; Sorption

Development of a new molecular dynamics method for tribochemical reaction and its application to formation dynamics of MoS₂ tribofilm by Yusuke Morita; Tasuku Onodera; Ai Suzuki; Riadh Sahnoun; Michihisa Koyama; Hideyuki Tsuboi; Nozomu Hatakeyama; Akira Endou; Hiromitsu Takaba; Momoji Kubo; Carlos A. Del Carpio; Takatoshi Shin-yoshi; Noriaki Nishino; Atsushi Suzuki; Akira Miyamoto (pp. 7618-7621).

Recently we have developed a novel molecular dynamics program NEW-RYUDO-CR, which can deal with chemical reactions. The developed method has been applied to the study of tribochemical reaction dynamics of MoS₂ tribofilm on iron surface. The initially amorphous MoS₂ layer self-organized its structure as result of the tribochemical reactions and formed layered MoS₂ tribofilm. The friction coefficient significantly decreased as the MoS₂ tribofilm was formed. Besides, sliding was observed between sulfur layers of MoS₂ tribofilms which occurred due to repulsive Coulombic interaction forces between sulfur atoms. This indicates that the formation of the layered MoS₂ tribofilm is important to achieve better lubrication properties.

Keywords: PACS; 31.15.−p; 31.15.at; 46.55.+d; 81.40PqMoS; ₂; tribofilm; New molecular dynamics method; Formation dynamics; Super-low friction; Chemical reaction

The electronic structure and reactivity of the oxygen-modified Mo₂C(0001) surface by K. Edamoto; Y. Nakadai; Y. Abe; K. Ozawa (pp. 7622-7625).

Oxygen adsorption on Mo₂C(0001) has been investigated with angle-resolved photoemission spectroscopy (ARPES). When the surface is reacted with O₂, the O 2p-induced states are formed at 4.1 and 5.3eV at theΓ¯ point. The emissions around the Fermi level are also intensified by oxygen adsorption, which is due to the formation of a partially filled state. It is found that the reactivity of the surface toward H₂O adsorption is much enhanced by pre-adsorption of oxygen. The reactivity is found to be maximized at θ_O∼0.2.

Keywords: Photoemission spectroscopy; Chemisorption; Carbides; Low index single crystal surfaces; Water

Pt-induced structures on Si(1 1 0) studied by STM by Anton Visikovskiy; Masamichi Yoshimura; Kazuyuki Ueda (pp. 7626-7629).

The structures induced by platinum (Pt) adsorption on Si(1 1 0) surface have been studied by scanning tunneling microscopy (STM) for coverage up to 2 monolayers (ML). Three surface phases have been found to form: “5×4”, “13×2” and “6×5” for Pt coverages 0.3, 0.5 and 1 ML respectively. All structures are formed by one-dimensional rows aligned along the[11¯0] direction. At the coverage>1 ML islands of, probably, Pt silicide start to form in form of 1D nanowires.

Keywords: Si(1 1 0); Platinum; STM; Nanowires

MOCVD growth of spherical aggregates of SiC nanocrystallites by Shuhei Takao; Hideo Kohno; Satoshi Ichikawa; Seiji Takeda (pp. 7630-7632).

Spherical aggregates of SiC nanocrystallites can be grown in addition to SiC nanowires via metal organic chemical vapor deposition using methylvinyldichlorosilane as a source gas and Ni catalyst by controlling the growth temperature and the pressure of the source gas. Electron microscopy observations show that the aggregates are typically 300nm in diameter, which consist of SiC nanocrystallites of about 5nm in diameter. Electron diffraction reveals that the nanocrystallites have the 3C structure.

Keywords: PACS; 61.46.; −; w; 68.37.HK; 68.37.Lp; 81.07.; −; bSiC nanostructures; MOCVD; Aggregate

Formation of multiple nanoscale twin boundaries that emit intense light in indirect-gap AlGaAs epilayers by Y. Ohno; K. Shoda; T. Taishi; I. Yonenaga; S. Takeda (pp. 7633-7637).

Parallel twin boundaries arranged at similar intervals of nanometer length, that emitted an intense monochromatic light polarized parallel to the boundaries, were self-organized in an indirect-gap AlGaAs epilayer; the epilayer was grown on a rough As-deficient surface of an AlGaAs(001) substrate with any lattice constant, by conventional metal-organic chemical-vapor deposition. Most boundaries were ofΣ3-type on{111}B, and they extended from the interface between the epilayer and the substrate. There existed no compositional fluctuation around the boundaries. The formation mechanism was discussed.

Keywords: Multiple nanoscale twin boundaries of; Σ; 3; -type; Indirect-gap AlGaAs epilayers; Transmission electron microscopy; Cathodoluminescence spectroscopy; CuPt-ordered AlGaAs

Surface restructuring process on a Ag/Ge(001) surface studied by photoelectron spectroscopy by Kan Nakatsuji; Takushi Iimori; Yasumasa Takagi; Daiichiro Sekiba; Shunsuke Doi; Masamichi Yamada; Taichi Okuda; Ayumi Harasawa; Toyohiko Kinoshita; Fumio Komori (pp. 7638-7641).

The atomic structure and charge distribution of Ag adsorbed Ge(001) surfaces have been investigated by means of Ge 3d core- and Ag 4d core-levels photoelectron spectroscopy. A mono-atomic layer of Ag was deposited on the clean Ge(001)c(4×2) surface at 80K. The Ge 3d spectrum measured at 80K was deconvoluted into two surface components, which is consistent with the previously proposed Ag ad-dimer model. After annealing the surface at room temperature, the rearrangement of the charge distribution was revealed to include electron transfer from Ge to Ag in conjunction with the surface restructuring process by the annealing.

Keywords: PACS; 73.20.; −; r; 79.60.; −; i; 79.60.JvSilver; Germanium; Surface; Electronic structure; Core-level shift; Photoelectron spectroscopy

One-dimensional atomic and electronic structures of submonolayer potassium deposited on stepped Ni(755) surface by Koji Ogawa; Shunsuke Harada; Koji Nakanishi; Hidetoshi Namba (pp. 7642-7646).

We deposited 0.01–0.16 ML (monolayer) of potassium on stepped (755) [=6(111)×(100)] surface of nickel in order to fabricate and to understand the growth process of one-dimensional (1D) potassium atomic-chain structure by observing the low-energy-electron-diffraction (LEED) patterns. The LEED patterns from potassium adsorbates exhibit a distinct coverage dependence that 1× streaks first appeared at low coverages up to 0.04 ML and later 2× streaks appeared at around 0.09 ML. The streaks become spotty at the higher coverage. We explained these coverage-dependent changes in LEED patterns in a thorough comparison with kinematically calculated LEED patterns constructing a reasonable growth model.

Keywords: PACS; 61.14.Hg; 73.22.f; 73.63.Nm; 79.60.JvAtomic chain; Potassium; Growth; Stepped single crystal surfaces; Nickel; Low-energy-electron-diffraction (LEED)

Magic clusters and(2×1) local structure formed in a half-unit cell of the Si(111)-(7×7) surface by Tl adsorption by P. Kocán; A.V. Visikovskiy; Y. Ohira; M. Yoshimura; K. Ueda; H. Tochihara (pp. 7647-7650).

Formation of a(2×1) local structure is found at submonolayer growth of Tl on the Si(111)-(7×7) surface by means of scanning tunneling microscopy (STM). At low coverages, the(7×7) grid remains and the(2×1) structure is formed inside of the half-unit cells of the(7×7). The(2×1) coexists with other structures, such as of “magic” clusters observed in the case of all other group III metals. Based on our STM observations we propose an atomic arrangement of the(2×1) structure.

Keywords: Scanning tunneling microscopy; Silicon; Thallium; Nanostructures

The characterization of EuO nanocrystals using synchrotron light by Packpoom Sukveeradachgul; Wanchai Pijitrojana (pp. 7651-7654).

We have studied the physical structure, optical property, electronic band structure and atomic structure of europium oxide (EuO) nanocrystals. The physical structures of nanocrystals are confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The optical property and electronic band structure are studied by X-ray absorption near-edge structure (XANES) measurement. We have also investigated the L₃-edge energy of europium(II) ion by extended X-ray absorption fine structure (EXAFS) measurement, which clarified the atomic structure of europium oxide nanocrystals.

Keywords: Europium oxide; Europium monoxide; Europium chalcogenide; Nanocrystal; EuO; XAS

Aluminium adsorption on Ir(111) at a quarter monolayer coverage: A first-principles study by Hong Zhang; Aloysius Soon; Bernard Delley; Catherine Stampfl (pp. 7655-7658).

We present an ab initio density-functional study for aluminium adsorption on Ir(111) at high symmetry sites, namely, the fcc-, hcp-hollow, top and bridge sites. In each case, we calculate the atomic geometry, average binding energy, work function, and surface dipole moment at the coverage of 0.25 monolayer. We find the favourable structure to be Al at threefold hcp-hollow site, with a corresponding binding energy of 4.46eV. We present and compare the electronic properties of the two lowest energy structures, i.e., at the threefold hollow sites and discuss the nature of the Al–Ir bond and binding site preference. In particular, we observe a large hybridization of Al-3s, 3p and Ir-5d states near Fermi level, forming an inter-metallic bonds. This results in a significant electron transfer from the Al atoms to the Ir(111) substrate, inducing an outward pointing surface dipole moment and a large decrease in the work function of 1.69eV for Al in the hcp-hollow site. Compared to the fcc-hollow site, adsorption in the hcp-hollow site results in a lower density-of-states at the Fermi level, as well as a greater hybridization in the bonding states.

Keywords: PACS; 81.65.Mq; 68.43.; −; h; 68.47.GhIridium; Binding energy; Aluminium adsorption; Work function; Density-functional theory

An ab initio-based approach to phase diagram calculations for GaN(0001) surfaces by Tomonori Ito; Tomoyuki Nakamura; Toru Akiyama; Kohji Nakamura (pp. 7659-7662).

Surface phase diagrams of GaN(0001)-(2×2) and pseudo-(1×1) surfaces are systematically investigated by using our ab initio-based approach. The phase diagrams are obtained as functions of temperature T and Ga beam equivalent pressure p_Ga by comparing chemical potentials of Ga atom in the vapor phase with that on the surface. The calculated results imply that the (2×2) surface is stable in the temperature range of 700–1000K at 10⁻⁸Torr and 900–1400K at 10⁻²Torr. This is consistent with experimental stable temperature range for the (2×2). On the other hand, the pseudo-(1×1) phase is stable in the temperature range less than 700K at 10⁻⁸Torr and less than 1000K at 10⁻²Torr. Furthermore, the stable region of the pseudo-(1×1) phase almost coincides with that of the (2×2) with excess Ga adatom. This suggests that Ga adsorption or desorption during GaN MBE growth can easily change the pseudo-(1×1) to the (2×2) with Ga adatom and vice versa.

Keywords: PACS; 31.15.AR; 68.35.MD; 68.47.Fg; 81.05.EaAb initio quantum chemical methods and calculations; Surface thermodynamics; GaN(0; 0; 0; 1)

An ab initio-based approach to phase diagram calculations for GaAs(001)-(2×4)γ surfaces by Tomonori Ito; Toru Akiyama; Kohji Nakamura (pp. 7663-7667).

Surface phase diagram of recently proposed GaAs(001)-(2×4)γ is systematically investigated by using our ab initio-based approach. We focus on the (4×7) domain consisting of c(4×4)-like and (2×4)-like regions to clarify surface dimer constituents as functions of temperature T and As (As₂ and As₄) pressure p_As by comparing chemical potentials of surface dimers in the vapor phase with that on the surface. The calculated results under As₄ imply that Ga dimers in the c(4×4)-like region tend to become stable with increase of temperature and appear at the conventional growth condition such as T∼800K and p_As∼10⁻⁶Torr, while the (2×4)-like region favors As dimers. This is consistent with temperature dependence of change in surface dimer constituents on the c(4×4) and (2×4)β2 clarified in our previous study. Furthermore, the surface phase transition from the c(4×4) to (2×4)β2 via (2×4)γ is discussed on the basis of the phase diagram obtained in this study.

Keywords: PACS; 31.15.AR; 68.35.MD; 68.47.Fg; 81.05.EaAb initio quantum chemical methods and calculations; Surface thermodynamics; GaAs(0; 0; 1)-(2; ×; 4)γ

Theoretical investigations on the formation of wurtzite segments in group III–V semiconductor nanowires by Tomoki Yamashita; Kosuke Sano; Toru Akiyama; Kohji Nakamura; Tomonori Ito (pp. 7668-7671).

Structural trends in group III–V semiconductor nanowires (NWs) are systematically investigated based on Monte-Carlo simulations using our empirical potential calculations. The calculated NW stacking sequences for the selective area growth demonstrate that the averaged periodicity between wurtzite segments, which is independent of the NW size, decreases with increasing ionicity of semiconductorsfi. It is also found that the periodicity is affected by the nucleus size of NWs: The calculated periodicity in InP (InAs) NWs with the nucleus size consisting of∼ 10 atoms are 0.76 (0.86) nm, reasonably consistent with the experimentally reported one. On the other hand, the nucleus size to reproduce the experimentally reported periodicity in GaAs NWs is estimated to be more than 70 atoms. These results thus imply that the nucleus size as well asfi is of importance in determining the averaged periodicity between wurtzite segments.

Keywords: PACS; 81.07.Bc; 81.10.−h; 61.46. +wNanowires; Monte-Carlo simulation; Rotational twins; Nucleus size; Ionicity

Theoretical investigation on structural stability of InN thin films on 3C–SiC(001) by Takumi Ito; Toru Akiyama; Kohji Nakamura; Tomonori Ito (pp. 7672-7675).

The structural stability of InN thin films on 3C–SiC(001) substrate is systematically investigated based on an empirical interatomic potential, which incorporates electrostatic energy due to covalent bond charges and ionic charges. The calculated energy differences among coherently grown 3C–InN(001), 3C–InN(001) with misfit dislocations (MDs), and 2H–InN(0001) imply that the coherently grown 3C–InN(001) is stable when the film thickness is less than 7 monolayers (MLs) while 2H–InN(0001) is stabilized for the thickness beyond 8 MLs. This is because InN layers in 2H–InN(0001) are fully relaxed by one MD. The analysis of atomic configuration at the 3C–InN(001)/3C–SiC(001) interfaces reveals that the coordination number of interfacial atoms is quite different from that in the bulk region. Thus, 3C–InN(001) with MDs on 3C–SiC(001) is always metastable over entire range of film thickness, consistent with the successful fabrication of 2H–InN(0001) on 3C–SiC(001) by the molecular beam epitaxy. These results suggest that the mismatch in atomic arrangements at the interface crucially affects the structural stability of InN thin films on 3C–SiC(001) substrate.

Keywords: PACS; 61.50.Ah; 68.55.ag; 81.10.AjInN; Thin films; Wurtzite structure; Zinc blende structure; Structural stability; Interatomic potential

The coloration of tungsten-oxide film by oxygen deficiency and its mechanism by Ryuji Sato; Norikazu Kawamura; Haruki Tokumaru (pp. 7676-7678).

The transmissivity and the optical absorption of a WO₃ film with oxygen deficiencies introduced were characterized and compared with those of an electrochromically colored WO₃ upon injecting a proton (H⁺). The WO₃ film with oxygen deficiencies introduced was clearly colored blue. It was shown that the wavelength regions of optical absorption of both films almost overlapped each other.

Keywords: PACS; 42.79.Vb/36.20.KdTungsten-oxide; Electrochromism; Oxygen deficiency; Absorption; Electron transition

Atomic orbitals and photoelectron intensity angular distribution patterns of MoS₂ valence band by Zs. Jánosfalvi; F. Matsui; N. Takahashi; M. Akasaka; H. Namba; Hiroshi Daimon (pp. 7679-7683).

The ratio of atomic orbitals contributing to the valence band can be determined from the photoelectron intensity angular distribution (PIAD) by using linearly polarized light and display-type spherical mirror analyzer. The experiment was done for MoS₂ using a linearly polarized light at the photon energy of 45eV perpendicularly incident to the sample surface. Atomic orbitals contributing to the bands near the Fermi level were investigated. The PIAD patterns around theΓ point showed splitting of intensity. The intensity at the top and bottomK points was strong, while the intensity was weak at the left and right side K points. The PIAD patterns from various kinds of atomic orbitals were calculated. By comparing the experimental PIAD patterns to the simulated ones, we concluded that at theΓ point Mo 4d z₂ and S 3p_z atomic orbitals are the main components and at the K points the Mo 4d_xy atomic orbital is dominant. The atomic orbital Mo 4d x2− y₂ also gives contribution to the PIAD pattern. These results were in good agreement with the coefficients of the atomic orbitals derived using ab initio band calculation.

Keywords: PACS; 73.20.AtDichalcogenides; Valence band; Angle-resolved photoelectron spectroscopy

Co-induced nano-structures on Si(111) surface by Y.T. Cui; T. Xie; M. Ye; A. Kimura; S. Qiao; H. Namatame; M. Taniguchi (pp. 7684-7687).

The interaction of cobalt atoms with silicon (111) surface has been investigated by means of scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). Besides the Co silicide islands, we have successfully distinguished two inequivalent Co-induced13×13 reconstructions on Si(111) surface. Our high-resolution STM images provide some structural properties of the two different13×13 derived phases. Both of the two phases seem to form islands with single domain. The new findings will help us to understand the early stage of Co silicide formations.

Keywords: PACS; 61.14.Hg; 61.30.Hn; 61.46.Bc; 68.35.; −; p; 73.20.AtCo silicide; Si(1; 1; 1) surface; Scanning tunneling microscopy; LEED; Reconstructions

Enhanced electrical properties of pentacene-based organic thin-film transistors by modifying the gate insulator surface by J.X. Tang; C.S. Lee; M.Y. Chan; S.T. Lee (pp. 7688-7692).

A reliable surface treatment for the pentacene/gate dielectric interface was developed to enhance the electrical transport properties of organic thin-film transistors (OTFTs). Plasma-polymerized fluorocarbon (CFx) film was deposited onto the SiO₂ gate dielectric prior to pentacene deposition, resulting in a dramatic increase of the field-effect mobility from 0.015cm²/(Vs) to 0.22cm²/(Vs), and a threshold voltage reduction from −14.0V to −9.9V. The observed carrier mobility increase by a factor of 10 in the resulting OTFTs is associated with various growth behaviors of polycrystalline pentacene thin films on different substrates, where a pronounced morphological change occurs in the first few molecular layers but the similar morphologies in the upper layers. The accompanying threshold voltage variation suggests that hole accumulation in the conduction channel-induced weak charge transfer between pentacene and CFx.

Keywords: PACS; 68.37.Ps; 68.55.−a; 85.30.TvPentacene; Organic thin-film transistor; Surface treatment

Mixed layer formation of copper overlayers on Ni(110) surface by T. Fukuda; K. Iwamoto; Y. Fujimoto; K. Umezawa; H. Nakayama (pp. 7693-7696).

Copper overlayer formation on the Ni(110) surface was studied by scanning tunneling microscopy (STM) in an ultrahigh vacuum. Atom-resolved STM images showed that initially deposited Cu is replaced with surface Ni atoms forming atom-size depressions on the Ni(110) terraces and a Ni-rich quasi-one-dimensional island along the[11¯0] direction. Further Cu deposition yields a mosaic structure on the islands, indicating Cu/Ni mixed layer formation. From the quantitative measurement of the Cu/Ni ratio on the substrate and the islands, impinging Cu will be replaced with surface Ni whereas expelled Ni and directly impinging Cu to the island form the mixed island. The number of Cu atoms in the islands, however, more than the directly impinging Cu, indicate significant Cu/Ni replacement at the periphery of the island.

Keywords: PACS; 68.35.Dv; 68.37.Ef; 68.47.De; 68.55.Nq; 81.10.BkMetal alloy; Scanning tunneling microscopy; Heteroepitaxy

Effect of alcohol sources on synthesis of single-walled carbon nanotubes by Satoshi Oida; Akira Sakai; Osamu Nakatsuka; Masaki Ogawa; Shigeaki Zaima (pp. 7697-7702).

The effect of oxidant species forming an alcohol molecule for hot-filament chemical vapor deposition (HFCVD) on single-walled carbon nanotubes (SWCNTs) growth has been investigated. To use a graphite rod as a filament for HFCVD to decompose alcohol sources, contamination-free sample surface can be obtained and SWCNTs are successively and densely grown at a lower temperature than those by conventional thermal CVD. It is found that the higher the molecule number of alcohol among CH₃OH, C₂H₅OH, and 2-C₃H₇OH is, the lower the initial growth rate of SWCNTs is. As for CH₃OH, diameter distribution of SWCNTs is dynamically changed with the growth time passed, and a negative growth rate is observed at the later stage of growth. The growth kinetics depending on the alcohol sources is discussed on the basis of a capability of the oxidant species to burn away SWCNTs and deactivation of Co catalysts used for the growth.

Keywords: Hot-filament chemical vapor deposition; Single-walled carbon nanotubes; Alcohol; Radical CVD

Catalyst formation at various temperatures by hydrogen radical treatment and synthesis of silicon nanowires by Minsung Jeon; Koichi Kamisako (pp. 7703-7707).

Metal nanocrystals as catalyst from a metal oxide film were fabricated at various temperatures after hydrogen radical treatment and great quantities of silicon nanowires (SiNWs) were successfully synthesized using the hydrogen microwave afterglow deposition method. Indium (In) metal nanocrystals with size of about 12nm were obtained from indium oxide film after hydrogen radical pre-treatment for 5min at 400°C and their quantity reached approximately 3×10¹⁰cm⁻². Subsequently, a numerous SiNWs were grown with the crystal diffraction of (111), (220) and (311). The diameters of the SiNWs mainly ranged from 5 to 120nm and their lengths extended to about 8.5μm.

Keywords: PACS; 61.46+w; 68.37.Hk; 68.37.Lp; 68.65.−k; 68.70.+wIndium catalyst; Nanocrystals; Metal oxide film; Silicon nanowires; Hydrogen radicals; FE-SEM; TEM

X-ray analysis of ZnO nanorods grown by microwave irradiation heating on ZnO films by K. Ogata; K. Koike; S. Sasa; M. Inoue; M. Yano (pp. 7708-7711).

Utilizing microwave irradiation heating, 100-nm-diameter ZnO nanorods were grown from aqueous solution on sputtered ZnO films on glass substrates. Its out-of-plane X-ray diffraction (XRD) measurement indicated that the ZnO nanorods were grown with c-axis orientation, similar with the underlying ZnO films. In the in-plane XRD measurement, intensity of the (112¯0) diffraction was comparable with that of the (101¯0) one, suggesting their intensity ratio would contain useful information on nanorods density.

Keywords: ZnO nanorods; X-ray diffraction

Intramolecular structures of C₆₀ and C₈₄ molecules on Si(111)-7×7 surfaces by scanning tunneling microscopy by Chih-Pong Huang; Chih-Chuan Su; Mon-Shu Ho (pp. 7712-7717).

The intramolecular features of carbon 60 and carbon 84 molecules on Si(111)-7×7 surfaces were studied under a UHV-scanning tunneling microscope. Carbon molecules preferentially appear in faulted halves, rather than in unfaulted halves and corner holes; they are embedded in silicon substrates. The orientation and details of the structure of carbon molecules are determined by applying various sample biases to the silicon substrate. As compared with other fullerenes, a bright pentagonal ring with nebulous clusters which represents the cage structure is clearly observed on top of carbon 60 molecules. The bright stripes associated with partitioned curves which depict eight features of asymmetrical C₈₄ molecules are also investigated on Si(111)-7×7 surfaces. The orientations and possible configurations of C₆₀ and C₈₄ are considered in this work. The energy differences for various features of C₆₀ and C₈₄ molecules are estimated and discussed. The corresponding models with respect to each intramolecular feature are proposed and compared with recent theoretical calculation.

Keywords: C; ₆₀; C; ₈₄; Si(1; 1; 1)-7; ×; 7; STM

Synthesis and electrochemical properties of Ni doped titanate nanotubes for lithium ion storage by Dong Hyun Kim; Ki Soo Lee; Ji Hoon Yoon; Jum Suk Jang; Duck-Kyun Choi; Yang-Kook Sun; Sun-Jae Kim; Kyung Sub Lee (pp. 7718-7722).

Ni doped titanate nanotubes were synthesized by hydrothermal method using Ni doped rutile TiO₂ nanopowders as a starting material. The electrochemical properties were investigated by cyclic voltammmetric methods. The microstructure and morphology of the synthesized powders were characterized by XRD (X-ray diffraction), and HRTEM (high resolution transmission electron microscopy). Ni doped nanotubes were composed of H₂Ti₂O₅·H₂O with outer and inner diameter of ∼10nm and 6nm and showed a initial discharge capacity of 305mAh/g with poor cycling performance. However, after firing, the Ni doped nanotubes revealed better cycling performance due to lower reaction with hydrate and smaller diameter of the tubes.

Keywords: PACS; 82.45.YzTitanate nanotubes; Hydrothermal method; Mechanical alloying

Influence of the vacuum level upon the growth of carbon nanotubes on silicon carbide surface by J. Yoshida; Y. Yonekubo; T. Nakanishi; H. Okado; M. Naitoh; T. Sakata; H. Mori (pp. 7723-7727).

We have investigated the influence of the vacuum level upon the growth of carbon nanotubes (CNTs) on 6H–SiC (0001¯) surface.CNTs of about 160nm in length were formed densely and uniformly on the 6H–SiC surface during annealing at 1700°C in a high vacuum (∼10⁻²Pa). CNTs of about 1μm in length were formed during annealing at 1700°C in an ultra-high vacuum (∼10⁻⁷Pa). However, CNTs were not formed and SiO₂ layers were formed on the SiC surface at 1700°C in air. It is found that longer CNTs can grow up in an ultra-high vacuum, moreover, a little aligned and low-density graphite layers, or carbon nanofibers can also grow up.

Keywords: PACS; 61.46.+w; 68.47.Fg; 68.37.Lp; 81.05.UwCarbon nanotubes; Silicon carbide; TEM; Carbon nanofiber

Molecular beam epitaxy of GaSb on ZnTe/GaAs: Influence of the chemical composition of ZnTe surface by Woong Lee; Siyoung Kim; Joonsuk Song; Hangju Ko; Takafumi Yao; Young-Rae Cho; Hongchan Lee; Sangtae Lee; Bonheun Koo; Jiho Chang (pp. 7728-7732).

We have studied the molecular beam epitaxy (MBE) of GaSb films on GaAs (001) substrates by using ZnTe as a new buffer layer. GaSb films were grown on two distinct ZnTe surfaces and the influence of surface chemical composition of ZnTe on the morphological and structural properties of GaSb films has been investigated. Initial 2-dimensional (2D) growth of GaSb films is obtained on Zn-terminated surface consequently smooth morphology and high crystal quality GaSb films are achieved. The thin GaSb film (0.4μm) grown on Zn-terminated ZnTe surface reveals considerably narrow X-ray diffraction linewidth (113arcsec) along with small residual strain, which strongly supports the availability of ZnTe buffer for the growth of high-quality GaSb film.

Keywords: Molecular beam epitaxy; Antimonides; Semiconducting III–V; Single crystal growth; X-ray diffraction

Quasi-one-dimensional In atomic chains on Si(111) at low temperature studied by reflection high-energy positron diffraction and scanning tunneling microscopy by M. Hashimoto; Y. Fukaya; A. Kawasuso; A. Ichimiya (pp. 7733-7736).

We have investigated a quasi-one-dimensional structure of Si(111)-8×2-In surface using reflection high-energy positron diffraction (RHEPD) and scanning tunneling microscopy (STM). From the RHEPD rocking curve analyses, we confirmed the formation of the In hexagon structure proposed by González et al. [C. González, F. Flores, J. Ortega, Phys. Rev. Lett. 96 (2006) 136101]. Furthermore, we found that the empty-state STM image at 44K is consistent with that calculated with the optimum hexagon structure by the RHEPD analyses.

Keywords: PACS; 68.35.B-; 61.05.jh; 68.37.EfSurface structure; Reflection high-energy positron diffraction (RHEPD); Scanning tunneling microscopy (STM); Silicon; Indium

Spatial resolution of imaging contaminations on the GaAs surface by scanning tunneling microscope-cathodoluminescence spectroscopy by Kentaro Watanabe; Yoshiaki Nakamura; Masakazu Ichikawa (pp. 7737-7741).

We obtained the luminescence image of the GaAs (110) surface by scanning tunneling microscope-cathodoluminescence (STM-CL) spectroscopy, where low-energy (∼100eV) electrons field emitted from the STM tip were used as a bright excitation source. The STM-CL image with high photon signal (1.25×10⁴cps) showed the dark image corresponding to the surface contamination in the STM image working as the nonradiative recombination centers of carriers. This dark image demonstrated the spatial resolution of about 100nm in STM-CL spectroscopy of the GaAs (110) surface, which was determined by the field-emitted electron beam diameter.

Keywords: Scanning tunneling microscopy; Cathodoluminescence; Field emission; GaAs

Numerical studies of electron transfers in two-dimensional multiple quantum dots by H. Kusumoto; S. Sakamoto; M. Tomiya (pp. 7742-7745).

Quantum dynamical properties of electron transfers through multiple quantum dots (QDs) are numerically investigated. The QDs are modeled as two-dimensional electron systems and the conductive properties are calculated from the time evolution of the electron wavefunctions. In addition, we propose a new technique dealing with the electron–electron correlation and demonstrate the dynamical simulations of the Coulomb blockade as well as the spin blockade.

Keywords: PACS; 73.63.Kv; 73.23.Hk; 03.65.GeQuantum dots; Electron transfer; Coulomb blockade; Spin blockade

Theoretical investigations for zinc blende–wurtzite polytypism in GaAs layers at Au/GaAs(111) interfaces by Yuya Haneda; Toru Akiyama; Kohji Nakamura; Tomonori Ito (pp. 7746-7749).

The zinc blende (ZB)–wurtzite (W) polytypism of GaAs layers at the Au/GaAs(111) B interfaces is investigated based on total-energy electronic-structure calculations within density functional theory. The calculations for the abrupt interfaces including a GaAs top layer with ZB and W stacking sequences reveal that the ZB sequence is energetically favorable, but the energy of W sequence with an interstitial Au atom at the top GaAs layer of the interface is lower than that of ZB sequence. This is because electrons accumulate around the interstitial region due to the hybridization between Au-6 s and As-4 p orbitals, resulting in the reduction of Ga–As bond charges. As a result, the relative stability at the top GaAs layer is determined by the electrostatic energy due to ionic charges. The results imply that the stabilization of W sequence at the Au catalyst–semiconductor interfaces as well as that on the nanowire faces are the origins for the appearance of W segments in NWs, qualitatively consistent with experiments.

Keywords: PACS; 61.72.uj; 62.23.Hj; 67.30.hp; 87.15.ANanowires; Wurtzite structure; Zinc blende structure; GaAs; Interface; Structural stability; First principles calculations

Hydrogen plasma enhanced alignment on CNT-STM tips grown by liquid catalyst-assisted microwave plasma-enhanced chemical vapor deposition by Fa-Kuei Tung; Masamichi Yoshimura; Kazuyuki Ueda; Yutaka Ohira; Takayoshi Tanji (pp. 7750-7754).

Carbon nanotubes are grown directly on a scanning tunneling microscopy tip by liquid catalyst-assisted microwave-enhanced chemical vapor deposition, and effects of hydrogen plasma treatment on the tip have been investigated in detail by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and Raman spectroscopy. The unaligned CNTs on the as-grown tip apex have been realigned and reshaped by subsequent hydrogen plasma treatment. The diameter of CNTs is enlarged mainly due to amorphous layers being re-sputtered over their outer shells.

Keywords: PACS; 01.30.CcHydrogen plasma; CNT; Alignment; SPM; CVD

Area effect of patterned carbon nanotube bundle on field electron emission characteristics by Ting-Wei Weng; Yu-Hao Lai; Kuei-Yi Lee (pp. 7755-7758).

Patterned carbon nanotube (CNT) bundles were fabricated using thermal chemical vapor deposition (CVD) method. Patterns of different diameters and distances were defined on Si(100) substrates using photolithography. CNT bundle height was controlled using different acetylene (C₂H₂) flow times. The inter-bundle distance of CNTs to CNT bundle height ratio was maintained at approximately 2, a number predicted to have a maximum field emission for CNT, and left the patterned CNT bundle area as a variable parameter. The relationship between CNT bundle area and the field electron emission characteristics was studied. The lowest threshold electric field ( E_th) of 0.7V/μm was obtained when the total area of patterned CNT bundles was approximately 46%. The result shows that there is an optimal CNT bundle area for electron field emission.

Keywords: PACS; 81.07.De; 81.15.Gh; 85.45.Db; 85.40.HpCarbon nanotube bundle; Field emission; Thermal chemical vapor deposition; Photolithography

Characterization of sp³ carbon produced by plasma deposition on gamma-TiAl alloys by Suparut Narksitipan; Titipun Thongtem; Somchai Thongtem (pp. 7759-7764).

Surfaces of two gamma-TiAl alloys, Ti–47%Al–2%Nb–2%Cr (MJ12) and Ti–47%Al–2%Nb–2%Mn+0.8%TiB₂ (MJ47), were modified by acetylene plasma deposition at −3kV bias voltage for 0.5–4h. By using GIXRD and SAED, C ( n-diamond), TiC, Al, AlTi, AlTi₂, AlTi₃, Al_0.64Ti_0.36 and Al₂Ti were detected on both alloys. Additional TiB₂ was detected on MJ47. XPS and Raman analyses revealed the presence of sp³ and sp² carbon deposited on the alloy surfaces with their binding energies of 283.9–284.8eV for MJ12 and 283.9–285.0eV for MJ47. Both sp³ and sp² contents were increased with the increase in the exposure times. The increasing rate of the first was less than that of the second, due to the stress developed in the films. Moiré fringe and crystallographic planes were detected using TEM. Knoop hardness of the deposited alloys, influenced by sp³ carbon, was increased with the increase in the exposure time. Those of MJ12 and MJ47 with 4h deposition are 1.88 and 1.57 times of the corresponding untreated alloys, respectively.

Keywords: PACS; 85.65.LpPlasma deposition; Gamma-TiAl alloys; sp; ³; carbon

Influence of cetyltrimethylammonium bromide on the morphology of AWO₄ (A=Ca, Sr) prepared by cyclic microwave irradiation by Titipun Thongtem; Sulawan Kaowphong; Somchai Thongtem (pp. 7765-7769).

AWO₄ (A=Ca, Sr) was prepared from metal salts [Ca(NO₃)₂·4H₂O or Sr(NO₃)₂], Na₂WO₄·2H₂O and different moles of cetyltrimethylammonium bromide (CTAB) in water by cyclic microwave irradiation. The structure of AWO₄ was characterized by X-ray diffraction (XRD) and selected area electron diffraction (SAED). Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) revealed the presence of nanoparticles in clusters with different morphologies; spheres, peaches with notches, dumb-bells and bundles, influenced by CTAB. Six Raman vibrational peaks of scheelite structure were detected at 908, 835, 793, 399, 332 and 210cm⁻¹ for CaWO₄ and 917, 833, 795, 372, 336 and 192cm⁻¹ for SrWO₄, which are assigned as ν₁(A_g), ν₃(B_g), ν₃(E_g), ν₄(B_g), ν₂(A_g) and ν_f.r.(A_g), respectively. Fourier transform infrared (FTIR) spectra provided the evidence of W–O stretching vibration in [WO₄]²⁻ tetrahedrons at 793cm⁻¹ for CaWO₄ and 807cm⁻¹ for SrWO₄. The peaks of photoluminescence (PL) spectra were at 428–434nm for CaWO₄, and 447–451nm for SrWO₄.

Keywords: PACS; 81.07.−bCyclic microwave irradiation; Nanostructured AWO; ₄; (A; =; Ca, Sr); Spheres; Peaches with notches; Dumb-bells; Bundles

Structural properties of GaAs nanostructures formed by a supply of intense As₄ flux in droplet epitaxy by T. Mano; K. Mitsuishi; Y. Nakayama; T. Noda; K. Sakoda (pp. 7770-7773).

We investigated detailed structural properties of GaAs nanostructures formed by a supply of intense As₄ flux to Ga droplets. Scanning electron microscopy (SEM) and cross-sectional transmission electron microscopy (TEM) revealed that whisker-like nanostructures had formed on the truncated cone-shaped bases after crystallization. Moreover, electron energy loss spectroscopy in scanning transmission electron microscopy (STEM-EELS) revealed that elemental Ga atoms remained inside the nanostructures while outside, some had crystallized into GaAs. These findings suggest that crystallization started at the edges of the droplets and the GaAs grew upward along the periphery of the droplets until the droplets were completely covered with crystallized GaAs.

Keywords: PACS; 68.70.+w; 68.37.−d; 68.37.Hk; 68.37.Lp; 79.20.Uv; 81.15.Hi; 61.30.Pq; 68.65.HpDroplet epitaxy; GaAs; Molecular beam epitaxy; Quantum dot; Whisker

Development of porous structure simulator for multi-scale simulation of irregular porous catalysts by Michihisa Koyama; Ai Suzuki; Riadh Sahnoun; Hideyuki Tsuboi; Nozomu Hatakeyama; Akira Endou; Hiromitsu Takaba; Momoji Kubo; Carlos A. Del Carpio; Akira Miyamoto (pp. 7774-7776).

Efficient development of highly functional porous materials, used as catalysts in the automobile industry, demands a meticulous knowledge of the nano-scale interface at the electronic and atomistic scale. However, it is often difficult to correlate the microscopic interfacial interactions with macroscopic characteristics of the materials; for instance, the interaction between a precious metal and its support oxide with long-term sintering properties of the catalyst. Multi-scale computational chemistry approaches can contribute to bridge the gap between micro- and macroscopic characteristics of these materials; however this type of multi-scale simulations has been difficult to apply especially to porous materials. To overcome this problem, we have developed a novel mesoscopic approach based on a porous structure simulator. This simulator can construct automatically irregular porous structures on a computer, enabling simulations with complex meso-scale structures. Moreover, in this work we have developed a new method to simulate long-term sintering properties of metal particles on porous catalysts. Finally, we have applied the method to the simulation of sintering properties of Pt on alumina support. This newly developed method has enabled us to propose a multi-scale simulation approach for porous catalysts.

Keywords: PACS; 61.43.Gt; 80.20.EvPorous catalyst; Pt/Al; ₂; O; ₃; Porous structure simulator; Sintering; Multi-scale simulation

Fabrication of a complex InAs ring-and-dot structure by droplet epitaxy by Takeshi Noda; Takaaki Mano (pp. 7777-7780).

An InAs ring structure accompanying the formation of quantum dots (QDs) was fabricated on (100)GaAs using droplet epitaxy. The QDs were located in the vicinity of the ring, due to the diffusion of In atoms from the In droplets. In addition, the dots were found to have distributed elliptically and preferentially along the [011] direction, implying that In itself prefers to diffuse along the [011] direction, which is the opposite of the favorable diffusion orientation of group III atoms on (100)GaAs under a commonly used As-stabilized growth condition. This is the first observation of a ring structure accompanying the formation of quantum dots in droplet epitaxy.

Keywords: PACS; 81.05.Ea; 81.07.Ta; 81.07.−b; 81.16.DnDroplet epitaxy; InAs; Ring; Quantum dot; Diffusion

Large-scale electronic structure calculation theory and applications to nanostructure materials by Takeo Fujiwara; Takeo Hoshi (pp. 7781-7785).

We review our recently developed methods in large-scale electronic structure calculations. The calculation is based on the tight-binding formalism of the Hamiltonian. First, the mathematical foundation of Krylov subspace method is focused. The density matrix can be calculated exactly and the numerical accuracy can be monitored during the iterative calculation. The key technique of the shifted-COCG (conjugate orthogonal conjugate gradient) method, collinear residual and seed switching, is explained in details. Second, several applications to nanostructure of semiconductors and metals, fracture propagation and surface reconstruction and formation process of gold nanowire, are explained.

Keywords: Large-scale electronic structure calculation; Nanostructure materials; Molecular dynamics; Order-; N; method; Krylov subspace theory; Fracture; Helical multi-shell nanowire; Silicon; GoldPACS; 61.46.; −; w; 71.15.Dx

The high quality ZnO growth on c-Al₂O₃ substrate with Cr₂O₃ buffer layer using plasma-assisted molecular beam epitaxy by J.S. Park; S.K. Hong; T. Minegishi; I.H. Im; S.H. Park; T. Hanada; J.H. Chang; M.W. Cho; T. Yao (pp. 7786-7789).

High quality epitaxial ZnO films were grown on c-Al₂O₃ substrates with Cr₂O₃ buffer layer by plasma-assisted molecular beam epitaxy (P-MBE). The hexagonal crystalline Cr₂O₃ layer was formed by oxidation of the Cr-metal layer deposited on the c-Al₂O₃ substrate using oxygen plasma. The epitaxial relationship was determined to be[11¯00]ZnO//[112¯0]Cr₂O₃//[11¯0]Cr//[112¯0]Al₂O₃ and[112¯0]ZnO//[11¯00]Cr₂O₃//[001]Cr//[11¯00]Al₂O_3. The Cr₂O₃ buffer layer was very effective in improving the surface morphology and crystal quality of the ZnO films. The photoluminescence spectrum showed the strong near band-edge emissions with the weak deep-level emission, which implies high optical quality of the ZnO films grown on the Cr₂O₃ buffer.

Keywords: PACS; 81.15.Hi; 78.55.Et; 81.65.MqZnO; Buffer; MBE; Cr; ₂; O; ₃

Luminescence studies on nitride quaternary alloys double quantum wells by S.C.P. Rodrigues; O.F.P. dos Santos; L.M.R. Scolfaro; G.M. Sipahi; E.F. da Silva Jr. (pp. 7790-7793).

We present theoretical photoluminescence (PL) spectra of undoped and p-doped Al_xIn1− x−_yGa_yN/Al_XIn1− X−_YGa_YN double quantum wells (DQWs). The calculations were performed within the k.p method by means of solving a full eight-band Kane Hamiltonian together with the Poisson equation in a plane wave representation, including exchange–correlation effects within the local density approximation. Strain effects due to the lattice mismatch are also taken into account. We show the calculated PL spectra, analyzing the blue and red-shifts in energy as one varies the spike and the well widths, as well as the acceptor doping concentration. We found a transition between a regime of isolated quantum wells and that of interacting DQWs. Since there are few studies of optical properties of quantum wells based on nitride quaternary alloys, the results reported here will provide guidelines for the interpretation of forthcoming experiments.

Keywords: PACS; 73.20 Dx, 78.55.−m, 79.60.Jv, 71.20.NPhotoluminescence; p-Type doping; Nitride semiconductors; Double quantum wells; AlInGaN quaternary alloys

Magnetic structures of exchange bias Ni/FeF₂(110) interface by Yusuke Ishihama; Kohji Nakamura; Toru Akiyama; Tomonori Ito (pp. 7794-7796).

Electronic and magnetic structures of ferromagnetic (FM)/antiferromagnetic (AFM), Ni/FeF₂(110), with a compensated AFM interface are investigated by using the full-potential linearized augmented plane-wave method. We find that magnetic structures at the AFM interface are perturbed by a contact with the FM material, where the superexchange interaction through the interface F excites and induces a small net moment at the AFM interface. These results predicted may play an important role for explaining the exchange bias in this system, and rule out the exchange bias mechanisms with the spin-flop coupling and the magnetic moment reorientation.

Keywords: PACS; 75.70.Cn; 75.50.Ee; 72.80.GaFerromagnetic/anti-ferromagnetic interfaces; FeF; ₂; First principles FLAPW calculations

Pd adsorption on Si(113) surface: STM and XPS study by Shinsuke Hara; Masamichi Yoshimura; Kazuyuki Ueda (pp. 7797-7802).

Pd-induced surface structures on Si(113) have been studied by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). In the initial process of the Pd adsorption below 0.10ML, Pd silicide (Pd₂Si) clusters are observed to form randomly on the surface. By increasing the Pd coverage to 0.10ML, the clusters cover the entire surface, and an amorphous layer is formed. After annealing the Si(113)-Pd surface at 600°C, various types of islands and chain protrusions appears. The agglomeration, coalescence and crystallization of these islands are observed by using high temperature (HT-) STM. It is also found by XPS that the islands correspond to Pd₂Si structure. On the basis of these results, evolution of Pd-induced structures at high temperatures is in detail discussed.

Keywords: PACS; 68.37.Ef; 68.43.Hn; 68.47.Fg; 68.55.−A; 79.60.−iPd; Si(1; 1; 3); Silicide; Cluster; Island; Scanning tunneling microscopy; X-ray photoelectron spectroscopy

Study of buried Si(111)-5×2-Au by surface X-ray diffraction by Yusaku Iwasawa; Wolfgang Voegeli; Tetsuroh Shirasawa; Kouji Sekiguchi; Takehiro Nojima; Ryuji Yoshida; Toshio Takahashi; Masuaki Matsumoto; Tatsuo Okano; Koichi Akimoto; Hiroshi Kawata; Hiroshi Sugiyama (pp. 7803-7806).

The structure of buried Si(111)-5×2-Au capped with amorphous Si was investigated using surface X-ray diffraction. It was found that the 5×2 structural periodicity is kept under the amorphous Si from the in-plane measurement. Furthermore, the intensity variation along the fractional-order rod indicates that Au atoms are located almost on the same plane.

Keywords: PACS; 61.10.Kw; 61.10.Nz; 68.35.−pSi(1; 1; 1)-5; ×; 2-Au; Surface X-ray diffraction; Buried interface

A Monte Carlo simulation study of H₂ layers on NaCl(001) by J.N. Dawoud; A.K. Sallabi; D.B. Jack (pp. 7807-7811).

Monte Carlo simulations show that, at one monolayer coverage, H₂ molecules adsorbed on a NaCl(001) surface occupy all Na⁺ sites and form a commensurate c(2×2) structure. If the Cl⁻ sites are occupied as well, a bi-layer p(2×1) structure forms. An examination of the H₂ molecules’ rotational motion shows the molecular axes are azimuthally delocalized and so both of the structures acquire (1×1) symmetry in accord with experimental observations. These calculations also show that helicoptering o-H₂ ( J=1, m=±1) prefer to sit on top of Na⁺ sites, while cartwheeling o-H₂ ( J=1, m=0) prefers to locate over Cl⁻ sites, in agreement with other work.

Keywords: Hydrogen; Deuterium; Quantum effects; Potential energy surface; Ortho; -hydrogen–; para; -hydrogen conversion; Monte Carlo simulations; NaCl

Enhancement effect in photon-stimulated ion desorption for benzene adsorbed on silicon surfaces observed using angle-dependent technique by Tetsuhiro Sekiguchi; Hiromi Ikeura-Sekiguchi; Yuji Baba (pp. 7812-7816).

We have investigated photon-stimulated ion desorption from deuterated benzene (C₆D₆) adsorbed on Si(100) and Si(111) surfaces following C 1s core excitation. Using time-of-flight mass spectrometry combined with angle-dependent technique, we measured the dependences of mass-spectra of desorption ions on photon energies and on incident angle ( θ) of synchrotron beam. We have found the ion yields for adsorbate-derived fragments of CD⁺ and CD₂⁺ are enhanced in very small angles of incident X-rays. Moreover, molecular orientation effect appeared in excitation energy dependences of D⁺ ions from the Si(100) and Si(111) surfaces; that is, ion yield spectra measured at θ=10° are different from that at θ=65°. Furthermore, it was found that desorption ion yields increase greatly with decreasing incident angles. The angular dependences are consistently similar for all ion species, excitation energies, and indexes of substrates. Possible desorption processes are described on the basis of the observations.

Keywords: Photon-stimulated desorption (PSD); Desorption induced by electronic transitions; Incident angle dependence; Inner-shell excitation; Benzene; Silicon; Near-edge X-ray absorption fine structures (NEXAFS)

A study on electrical and mechanical properties of hybrid-polymer thin films by a controlled TEOS bubbling ratio by S.-J. Cho; I.-S. Bae; H.-D. Jeong; J.-H. Boo (pp. 7817-7820).

Organic–inorganic hybrid-polymer thin films were deposited on silicon(100) substrates at room temperature by PECVD (plasma enhanced chemical vapor deposition). Ethylcyclohexane and TEOS (tetraethoxysilane) were utilized as organic and inorganic precursors with hydrogen gas for the ethylcyclohexane bubbler and argon gas for both the TEOS bubbler and as a carrier gas. To compare the electrical and the mechanical properties of the plasma polymerized thin films, we grew the hybrid-polymer thin films under conditions of various TEOS bubbling ratios. MTS nano-indenter was used to measure the hardness and Young's modulus and showed that these values increased as the TEOS bubbling ratio increased, with the highest hardness at 0.8GPa in this experiment. An impedance analyzer was utilized for the measurements of I– V curves and capacitance, showing the lowest dielectric constant at approximately 1.83, with a leakage current density of 10⁻⁸A/cm² at 1MV/cm, respectively.

Keywords: Organic–inorganic hybrid-polymer thin film; PECVD; low-; k; Electrical and mechanical properties

Selective growth of stacked InAs quantum dots by using the templates formed by the Nano-Jet Probe by S. Ohkouchi; Y. Sugimoto; N. Ozaki; H. Ishikawa; K. Asakawa (pp. 7821-7823).

We have demonstrated the selective area growth of stacked self-assembled InAs quantum dot (QD) arrays in the desired regions on a substrate and confirmed the photoluminescence (PL) emission exhibited by them at room temperature. These InAs QDs are fabricated by the use of a specially designed atomic force microscope cantilever referred to as the Nano-Jet Probe (NJP). By using the NJP, two-dimensional arrays with ordered In nano-dots are fabricated in the desired square regions on a GaAs substrate and directly converted into InAs QD arrays through the subsequent annealing by the irradiation of As flux. By using the converted QD arrays as strain templates, self-organized InAs QDs are stacked. These stacked QDs exhibit the PL emission peak at a wavelength of 1.02μm.

Keywords: PACS; 75.41Vx; 72.45Yn; 71.78.AgAtomic force microscope; Site-control; Quantum dots; InAs

Surface structure analysis of metal adsorbed Si(111) surfaces by Patterson function with LEED I– V curves by T. Kuzushita; A. Murata; A. Yamamoto; T. Urano (pp. 7824-7826).

Wu and Tong proposed the calculation method of Patterson function obtained directly from the LEED I– V curves which shows the relative position of surface atoms as an image. We have made the calculation program of Patterson function and applied to the structural analysis of the Si(111)1×1-Fe surface. Surface structure was able to be expressed almost correctly by the Patterson function obtained from the theoretical I– V curves for the model structure. In the Patterson function obtained from the experimental I– V curves, the locational relation between the atoms of subsurface layer was in agreement with the CsCl type structure. More over, because the faint peak, by which we can distinguish the model, can be seen, it seems that the model B8 is preferable to the model A8. This result is consistent with the model shown by Walter et al.

Keywords: LEED; I; –; V; curves; Patterson function; Si(1; 1; 1)1; ×; 1-Fe

Surface structure and phase transition of Ge(111)-3×3-Pb studied by reflection high-energy positron diffraction by Y. Fukaya; M. Hashimoto; A. Kawasuso; A. Ichimiya (pp. 7827-7830).

We studied the structures and the phase transition of Pb/Ge(111) surface by using the reflection high-energy positron diffraction. The surface structures at 60K and 293K have the 3×3 and √3×√3 periodicities, respectively. The rocking curves measured at both temperatures are nearly the same. This indicates that the equilibrium positions of the surface atoms do not change according to the phase transition. From the analysis of the rocking curve based on the dynamical diffraction theory, we found that at both temperatures the surface structures are composed of the so-called one-up and two-down model. The 3×3–√3×√3 phase transition for the Pb/Ge(111) surface is interpreted in terms of order–disorder transition.

Keywords: PACS; 68.35.Rh; 68.35.Bs; 61.14.HgPhase transition; Surface structure; Reflection high-energy positron diffraction (RHEPD); Total reflection; Germanium; Lead

Dynamic study of W atoms and clusters on W (111) surfaces by T.Y. Fu; W.J. Weng; T.T. Tsong (pp. 7831-7834).

Using a field ion microscope, the diffusion behaviors and atomic processes of W atoms and clusters on W (111) surfaces were observed directly. The activation energy of W clusters diffusion on W (111) as a function of cluster size has an oscillatory and increasing behavior. But, the activation energy of a single W atom is especially high. The compact geometric structures are more stable and have higher activation energies of surface diffusion than structures with extra atoms at the periphery. Besides the terrace diffusion, other atomic processes such as the ascending, descending, detachment motion on W (111) surfaces were also observed. Unlike the general systems, their occurrence temperatures are quite near. These experimental results were used to discuss the formation mechanism of single atom W tips.

Keywords: Field ion microscopy; Single atom tip; Surface thermodynamics; Tungsten

Adsorption structure and work function of dicarboxylic acid on Cu(110) surface by Shinjiro Yagyu; Michiko Yoshitake; Toyohiro Chikyow (pp. 7835-7837).

We investigated the relation between work function and the adsorption structure of dicarboxylic acids (organic molecules) such as succinic acid (HOOC–CH₂–CH₂–COOH) and an adipic acid (HOOC–(CH₂)₄–COOH) on a Cu(110) surface (electrode) as a function of the surface temperature using a Kelvin probe (KP). The work function changes of the two acids are similar. The work function increases by adsorption at room temperature due to ionization of molecules and then decreases with increasing temperature until 450K due to the effects of change in the dipole moment of the conformational change of the molecule. From 450 to 600K, the work function is constant because of competition between desorption and change in the dipole moment of molecules. It then reached the clean-surface value. Experiments clarified that the work function was affected by the adsorbed difference in conformation of molecules.

Keywords: PACS; 68.43.Fg (adsorbate structure (binding sites, geometry))Work function; Copper; Carboxylic acid; Adsorption; Molecular dipole

Atomically controlled surfaces with step and terrace of β-Ga₂O₃ single crystal substrates for thin film growth by Shigeo Ohira; Naoki Arai; Takayoshi Oshima; Shizuo Fujita (pp. 7838-7842).

The surface of β-Ga₂O₃ (100) single crystal grown with floating zone method was treated by chemical–mechanical-polishing (CMP) for 30–120min followed by annealing in oxygen atmosphere at temperature 600–1100°C for 3–6h. The evolution of the step arrangement was investigated with reflection high energy electron diffraction and atomic force microscopy. Atomically smooth surfaces with atomic step and terrace structure of β-Ga₂O₃ substrates were successfully obtained after just CMP treatment as well as CMP treatment and post annealing at 1100°C for 3h. The uniform step height was 0.57nm, and smooth terrace width was 100nm, where the misorientation angle was about 0.36°. The obtained atomically smooth surface provides a potential application for the high-quality epitaxial film growth.

Keywords: PACS; 61.05.jh; 61.66.Fn; 81.65.PsKeyword; β-Ga; ₂; O; ₃; Step and terrace structure; RHEED; AFM

Magnetic structures and magnetocrystalline anisotropy in bulk and thin film Fe₃Pt by H. Suzuki; K. Nakamura; T. Akiyama; T. Ito (pp. 7843-7845).

Magnetic structures and magnetocrystalline anisotropy (MCA) of tetragonal phase Fe₃Pt with an L1₂ atomic ordering in bulk and thin film are investigated by means of the first-principles full-potential linearized augmented plane-wave method. The results obtained predict that the tetragonal phase, in which the tetragonal distortion with ( c/ a)=0.95 makes an asymmetry of magnetic properties along the c-axis (out-of-plane) and a-axis (in-plane), has an out-of-plane MCA. In addition, from the thin film calculations, the presence of surface is found to strongly enhance the out-of-plane MCA.

Keywords: PACS; 75.30.Gw; 75.70.Ak; 75.70.RfFe; ₃; Pt; Magnetocrystalline anisotropy; First principles FLAPW calculations

Chitin–humic acid hybrid as adsorbent for Cr(III) in effluent of tannery wastewater treatment by Sri Juari Santosa; Dwi Siswanta; Sri Sudiono; Ratna Utarianingrum (pp. 7846-7850).

Adsorption of Cr(III) from both synthetic and real samples of tannery wastewater treatment's effluent on chitin–humic acid (chitin–HA) hybrid has been carried out. Rate constant and capacity of adsorption of Cr(III) from the synthetic sample were investigated and removal of Cr(III) from the real sample was tested at optimum medium acidity equivalent to pH 3.5. Characterization using Fourier transform infra red (FT-IR) spectroscopy revealed that bothCOO⁻ and N-acetyl originated from respectively humic acid (HA) and chitin were involved on the adsorption of Cr(III), and hence the Freundlich's multilayer and multi-energy adsorption model was more applicable to treat the adsorption data than the Langmuir's monolayer and mono-energy model. The quantification of adsorption capacity and rate constant using Freundlich isotherm model and first order adsorption reaching equilibrium yielded values of 6.84×10⁻⁴molg⁻¹ (35.57mgg⁻¹) and 1.70×10⁻²min⁻¹, respectively. Removal test for the real wastewater treatment's effluent showed that the maximum amount of Cr(III) could be removed by 1g of chitin–HA hybrid was 2.08×10⁻⁴mol or equivalent to 10.82mg.

Keywords: PACS; 61.18.−j; 61.25.Hq; 61.43.ErChitin–humic acid hybrid; Adsorbent; Removal; Cr(III); Tannery wastewater

Photomodulated reflectance study on optical property of InN thin films grown by reactive gas-timing rf magnetron sputtering by S. Porntheeraphat; J. Nukeaw (pp. 7851-7854).

The photoreflectance (PR) spectroscopy has been applied to investigate the band-gap energy ( E_g) of indium nitride (InN) thin films grown by rf magnetron sputtering. A novel reactive gas-timing technique applied for the sputtering process has been successfully employed to grow InN thin films without neither substrate heating nor post annealing. The X-ray diffraction (XRD) patterns exhibit strong peaks in the orientation along (002) and (101) planes, corresponding to the polycrystalline hexagonal-InN structure. The band-gap transition energy of InN was determined by fitting the PR spectra to a theoretical line shape. The PR results show the band-gap energy at 1.18eV for hexagonal-InN thin films deposited at the rf powers of 100 and 200W. The high rf sputtering powers in combination with the gas-timing technique should lead to a high concentration of highly excited nitrogen ions in the plasma, which enables the formation of InN without substrate heating. Auger electron spectroscopy (AES) measurements further reveal traces of oxygen in these InN films. This should explain the elevated band-gap energy, in reference to the band-gap value of 0.7eV for pristine InN films.

Keywords: Photoreflectance spectroscopy; InN; Reactive gas-timing; rf Sputtering

Phase stability in substitutionally Mn-doped GaAs: Role of lattice constraint by Kohji Nakamura; Toru Akiyama; Tomonori Ito (pp. 7855-7857).

Phase stability of Ga_xMn1−_xAs alloy with a zincblende structure over the whole Mn composition is investigated by means of the full-potential linearized augmented plane-wave method and the cluster expansion method, and role of a lattice constraint from substrate on the phase stability is discussed. The calculated results demonstrate a phase separated type phase diagram with a miscibility gap even when the lattice constraint by changing the lattice constant is imposed, where the critical temperature is found to decrease with increasing the lattice constant. Thus, the elastic constraint from the substrate acts to help stabilize a solid solution so as to realize the magnetic semiconductor with higher Mn composition.

Keywords: PACS; 75.50.Pp; 64.75.+gPhase stability; Magnetic semiconductor; Lattice constraint

Impact of surface step heights of 6H–SiC (0001) vicinal substrates in heteroepitaxial growth of 2H–AlN by H. Okumura; M. Horita; T. Kimoto; J. Suda (pp. 7858-7860).

Impact of step height of silicon carbide (SiC) substrates on heteroepitaxial growth of aluminum nitride (AlN) was investigated. Step-and-terrace structures with various step heights, 6 monolayer (ML), 3ML and 1ML, were formed on 6H–SiC (0001) vicinal substrates by high-temperature gas etching. 2H–AlN layers were grown on the substrate by plasma-assisted molecular-beam epitaxy (MBE) and then these layers were characterized by atomic-force microscopy (AFM) and X-ray diffraction (XRD). High-quality AlN can be grown on SiC substrates with 6ML- and 3ML-height step, while AlN grown on SiC substrates with 1ML-height step exhibited inferior crystalline quality. A model for high-quality AlN growth on SiC substrates with 3ML-height step is proposed.

Keywords: PACS; 81.05.Ea; 81.15.Hi; 68.37.Ps; 61.10.NzAlN; SiC; MBE; XRD; Surface control

Modeling tip performance for combined STM-luminescence and aperture-SNOM scanning probe: Spatial resolution and collection efficiency by Ilya Sychugov; Hiroo Omi; Tooru Murashita; Yoshihiro Kobayashi (pp. 7861-7863).

Finite-element simulations of the performance of the tip intended for use in combined aperture-SNOM and the scanning tunneling microscope (STM)-luminescence microscopy are presented. Tip geometry and the role of the opening in the protective metal coating were addressed. It is shown that the tip shape can affect transmittance for the excitation SNOM mode by nearly two orders of magnitude and the metal coating can enhance collection efficiency for the STM-luminescence mode. Desired tip configuration can be chosen based on the interplay between the improving collection efficiency and the deteriorating spatial resolution with increasing opening size.

Keywords: PACS; 87.64.Dz; 87.64.XxLuminescence; Near-field; STM; SNOM

Quasi-one-dimensional structures on the Si(111) surface induced by Ba adsorption by Geunseop Lee (pp. 7864-7867).

Ba-induced quasi-one-dimensional reconstructions of the Si(111) surface have been investigated by low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). While the 3×‘2’ surface shows double-periodicity along the stripes in STM images consistent with half-order streaks observed in LEED patterns, no sign of the double-periodicity along the chain direction was detected for the 5×1 surface. The 5× stripes in STM images show internal structures with multiple rows. The two rows comprising the boundaries of a 5× stripe in the filled-state STM image are found to have 3 a×√3/2 spacing across the stripe. The observation of the successive 3× and 2× spacings between the boundary rows supports a structural model proposed for the Ba-induced 5×1 Si reconstruction composed of honeycomb chains and Seiwatz chains. The highest coverage 2×8 surface does not reveal a quasi-1D row structure in STM images.

Keywords: PACS; 68.37.Ef; 68.47.Fg, 68.35.BsSi(1; 1; 1); Ba; Surface reconstruction; Scanning tunneling microscope; Low-energy electron diffraction

In situ monitoring of nucleation and evolution of Ge nanodots on faintly oxidized Si(111) surfaces by Sung-Pyo Cho; Shinji Kawano; Nobuo Tanaka (pp. 7868-7871).

We have investigated the nucleation and evolution of germanium (Ge) nanodot (ND)s taking place while depositing Ge onto the silicon (Si) (111) surfaces with ultra-thin Si oxide films by using ultra-high vacuum in situ high-resolution transmission electron microscopy in the profile-imaging geometry. Various types of growth phenomena such as nucleation, growth and coalescence of Ge NDs have successfully been observed. The results show that the growth phenomena of the Ge NDs are dramatically rapid after their size reaches the size of the critical nucleus. The critical nucleus size estimated from a model using the cohesive energy of the Ge NDs has been consistent with observed one.

Keywords: UHV; in situ; HR-profile TEM; Ge nanodot; Epitaxial growth; The critical nucleus

ARPES measurements on Si(111) hole subband induced by Pb and Ga adsorption by M. Morita; S.N. Takeda; M. Yoshikawa; A. Kuwako; Y. Kato; H. Daimon (pp. 7872-7876).

The subband dispersions in the Si(111) p-type inversion layers induced by Pb and Ga adsorbed surface structures were measured by angle-resolved photoemission spectroscopy (ARPES). The surface structures used here wereSi(111)33×33−PbGa and Si(111)6.3×6.3–Ga.Si(111)33×33−PbGa is a new surface phase found in this study. Because it is significant in our study to investigate potential effects of surface superstructures on the hole subband dispersion, we investigated the subband energy levels quantitatively comparing them with those calculated using the triangular approximation. It was found that the energy separation of the adjacent subband quantum levels in the inversion layers induced by gallium adsorption does not follow the triangular approximation. The possible band bending shape was proposed to explain the quantum level spacing of the subbands in Ga-induced inversion layers.

Keywords: Subband dispersion; ARPES; Si(1; 1; 1)

Elastic modulus of suspended purple membrane measured by atomic force microscopy by Ari M. Siitonen; Koji Sumitomo; Chandra S. Ramanujan; Youichi Shinozaki; Nahoko Kasai; Kazuaki Furukawa; John F. Ryan; Keiichi Torimitsu (pp. 7877-7880).

We have probed the mechanical properties of purple membrane (PM) in a physiological environment using the atomic force microscope (AFM). By suspending PM over nano-trenches, the elastic properties of PM can be evaluated free from the interaction with the substrate. Force–displacement curves were obtained on the suspended membrane and the data was compared to that of a simple model of a thin film over a trench. By fitting the data to the model, the elastic modulus of PM was estimated to be 8MPa. When the membrane is repeatedly indented, we observed a change in the force–distance data consistent with damage to the two-dimensional crystal of PM. In this paper we demonstrate that the AFM allows us to evaluate the mechanics of biological membranes in their native conditions.

Keywords: Nanobiotechnology; Scanning probe microscopy; Membrane protein; Elastic modulus

Giant fullerenes formed on C₆₀ films irradiated with electrons field-emitted from scanning tunneling microscope tips by Yoshiaki Nakamura; Yutaka Mera; Koji Maeda (pp. 7881-7884).

It has been found that spherical large clusters of carbon atoms are formed by irradiation of crystalline C₆₀ films grown on Si(111)-(7×7) surfaces with electrons field-emitted from a scanning tunneling microscope probe tip. The size distribution of the clusters deduced from surface profile measurements suggests that the dominant clusters were not necessarily C60_n ( n=2–4) expected from the simple fusion of C₆₀ molecules. It was proposed that electronic excitations of C₆₀ molecules caused the fragment and coalescence of the molecules to form the giant fullerenes as in the photo-induced similar effects.

Keywords: Giant fullerene; Electronic excitation; Electron irradiation; Fragmentation, Coalescence, STM

Structure and morphology of CuPc and F₁₆CuPc pn heterojunction by Rongbin Ye; Mamoru Baba; Kazunori Suzuki; Kunio Mori (pp. 7885-7888).

This article reports structure and morphology of copper phthalocyanine (CuPc) and fluorinated copper phthalocyanine (F₁₆CuPc) pn heterojunction. Highly ordered CuPc and F₁₆CuPc polycrystalline thin films with the 200 plane spacing s of 1.30 and 1.56nm, respectively, could be continuously grown via an intermediate-phase layer. Compared with CuPc, the intermediate-phase layer is much thinner when F₁₆CuPc is used as the first layer. The rougher the first layer is, the thicker the intermediate-phase layer is. Similarly, the 200 plane spacings of the intermediate-phase layer are dependent on morphology of the first layer. Furthermore, morphology of the heterostructure is mainly dominated by that of CuPc films. Due to the thicker intermediate-phase layer in the CuPc/F₁₆CuPc heterostructure, the thin film transistors (TFT) performance is obviously inferior to that of the F₁₆CuPc/CuPc device.

Keywords: Organic thin films; pn junction; Morphology; Ambipolar transport; Field-effect mobility

Spatial imaging of valence band electronic structures in a GaSb/InAs quantum well by K. Suzuki; K. Kanisawa; S. Perraud; T. Fujisawa (pp. 7889-7892).

We measure local density of states (LDOS) for GaSb/InAs heterostructures with quantum wells in the valence band by scanning tunneling spectroscopy (STS) on the cleaved surface. Clear standingwave patterns of LDOS corresponding to the holes confined in the quantum wells are observed.

Keywords: PACS; 73.21.Cd; 68.37.Ef; 81.05.Ea; 81.15.HiValence band; Quantum well; Scanning tunneling spectroscopy; Local density of states; Semiconductor heterostructures

Waveguide properties and optical switching of prism-coupled Au:SiO₂ nanocomposite films by K.S. Lee; S. Cho; S. Lee; T.S. Lee; W.M. Kim (pp. 7893-7896).

In this study, we present theoretical and experimental analyses on the waveguide mode properties of prism-coupled Au:SiO₂ nanocomposite films with the near infrared laser of 1550nm wavelength where the optical absorption diminished enough for the generation of guided mode. The evolution of guided mode in the nanocomposite waveguide and its propagation properties were also evaluated. As an effective way of utilizing the surface plasmon resonance properties for the application to optical switching devices, we employed an attenuated total internal reflection type optical switch geometry and tested its effectiveness for the absorptive opto-functional materials system using a cross-modulation technique with 532-nm pump and 1550-nm probe beams. The index change probe beam experiences was found to be purely refractive in nature and negative in sign, presumably due to the photo-thermal effect induced in the nanocomposite film by the irradiation of pump beam.

Keywords: PACS; 78.67.Bf; 81.07.b; 42.79.TaSurface Plasmon; Nanocomposite; Prism-coupler; Optical switching

Manipulation and soldering of carbon nanotubes using atomic force microscope by Yuta Kashiwase; Takayuki Ikeda; Takahide Oya; Toshio Ogino (pp. 7897-7900).

Manipulation of carbon nanotubes (CNTs) by an atomic force microscope (AFM) and soldering of CNTs using Fe oxide nanoparticles are described. We succeeded to separate a CNT bundle into two CNTs or CNT bundles, to move the separated CNT to a desirable position, and to bind it to another bundle. For the accurate manipulation, load of the AFM cantilever and frequency of the scan were carefully selected. We soldered two CNTs using an Fe oxide nanoparticle prepared from a ferritin molecule. The adhesion forces between the soldered CNTs were examined by an AFM and it was found that the CNTs were bound, though the binding force was not strong.

Keywords: PACS; 81.07.De; 68.37.Ps; 82.37.GkCarbon nanotube (CNT); Atomic force microscope (AFM); Molecular manipulation; Soldering; Fe nanoparticle; Ferritin molecule

Temperature dependence characterization of metal–insulator–nonuniformly-doped semiconductor solar cell by Mahmoud Shaban; M. Abdel-Gawad El-Sayed (pp. 7901-7904).

Four layered metal–insulator–pp⁺ semiconductor MIS solar cell device was simulated using a comprehensive numerical model. The semiconductor layer was assumed to be nonuniformly-doped in which additional drift electric field inside the semiconductor could be generated. The effects of the electrostatic and kinetic properties of the electronic states at the insulator-semiconductor interface were taken into account. The influences of the operating temperature on the device performance were studied in detail.

Keywords: MIS solar cell; Nonuniform doping profile; Temperature dependence; J; –; V; characteristics; Interface states

Electrical characteristics of polycrystalline Si layers embedded into high- k Al₂O₃ gate layers by Byoungjun Park; Kyoungah Cho; Sangsig Kim (pp. 7905-7908).

The electrical characteristics of polycrystalline Si (poly Si) layers embedded into high- k Al₂O₃ (alumina) gate layers are investigated in this work. The capacitance versus voltage ( C– V) curves obtained from the metal–alumina–polysilicon–alumina–silicon (MASAS) capacitors exhibit significant threshold voltage shifts, and the width of their hysteresis window is dependent on the range of the voltage sweep. The counterclockwise hysteresis observed in the C– V curves indicates that electrons originating from the p-type Si substrate in the inversion condition are trapped in the floating gate layer consisting of the poly Si layer present between the top and bottom Al₂O₃ layers in the MASAS capacitor. Also, current versus voltage ( I– V) measurements are performed to examine the electrical characteristics of the fabricated capacitors. The I– V measurements reveal that our MASAS capacitors show a very low leakage current density, compared to the previously reported results.

Keywords: PACS; 77.55.+f; 85.50.−n; 73.40.QvAlumina; Polycrystalline silicon; Memory; High-; k

Hybrid-DFT study for the initial oxidation steps on silicon cluster surface by Kenji Imamura; Kazuyuki Edamoto; Hiroaki Tokiwa (pp. 7909-7912).

We performed a hybrid density functional theory calculation for the successive adsorption of nitrous oxide (N₂O) on Si(100)-Si₉H₁₂O_x ( x=0 and 1) cluster surfaces to elucidate N₂O decomposition and the subsequent surface oxidation processes. N₂O decomposed into N₂ and O fragments, and the latter fragment inserted into either surface-dimer bonds or back-bonds with similar activation barriers on both the clean and partially oxidized Si surfaces. The Si₉H₁₂ cluster surface was eventually oxidized to five distinct structures of Si₉H₁₂O₂.

Keywords: Silicon surfaces; Density functional theory calculation; Nitrous oxide; Oxidation

Growth and characterization of ZnSe/CdSe/ZnSe quantum dots fabricated by using an alternate molecular beam supplying method by M. Ii; M. Ohishi; M. Yoneta; Y. Sato; M. Shintani; K. Yoshino; H. Saito (pp. 7913-7917).

ZnSe/CdSe/ZnSe structures inserted CdSe thin layer are fabricated using an alternate molecular beam supply (ALS). Examining the PL peak energy dependence on beam irradiation time in ALS cycle, we studied the initial stage of CdSe growth. When CdSe below the critical thickness is supplied on ZnSe grown on GaAs (100), two kinds of 2D islands (platelets) appear. We confirmed the alloying of 2D-CdSe islands and 3D-CdSe islands (dots) is prominent under Cd beam irradiation in ALS growth.

Keywords: PACS; 78.55Et; 78.67.Hc; 81.16.DnCdSe; Quantum dot; Molecular beam epitaxy; Photoluminescence; Critical thickness

Reactive ion etching of FePt using inductively coupled plasma by Tomomi Kanazawa; Kohei Ono; Masato Takenaka; Masashi Yamazaki; Kenichi Masuda; Shiho Cho; Takayuki Wakayama; Fumiyoshi Takano; Hiro Akinaga (pp. 7918-7920).

We propose a reactive ion etching (RIE) process of an L1₀-FePt film which is expected as one of the promising materials for the perpendicular magnetic recording media. The etching was carried out using an inductively coupled plasma (ICP) RIE system and an etching gas combination of CH₄/O₂/NH₃ was employed. The L1₀-FePt films were deposited on (100)-oriented MgO substrates using a magnetron sputtering system. The etching masks of Ti were patterned on the FePt films lithographically. The etch rates of ∼16 and ∼0nm/min were obtained for the FePt film and the Ti mask, respectively. The atomic force microscopy (AFM) analyses provided the average roughness ( R_a) value of 0.95nm for the etched FePt surface, that is, a very flat etched surface was obtained. Those results show that the highly selective RIE process of L1₀-FePt was successfully realized in the present study.

Keywords: PACS; 52.77.Bn (Etching and cleaning); 81.65.Cf (Surface cleaning, etching, patterning); 75.50.Bb (Fe and its alloys); 75.50.Ss (Magnetic recording materials)Reactive ion etching; Plasma; Magnetic material; FePt; Ti

Surface modification by vacuum annealing for field emission from heavily phosphorus-doped homoepitaxial (111) diamond by Takatoshi Yamada; Christoph E. Nebel; Kumaragurubaran Somu; Shin-ichi Shikata (pp. 7921-7924).

The relationship between field emission properties and C 1s core level shifts of heavily phosphorus-doped homoepitaxial (111) diamond is investigated as a function of annealing temperature in order to optimize surface carbon bonding configurations for device applications. A low field emission threshold voltage is observed from surfaces annealed at 800°C for hydrogen-plasma treated surface, while a low field emission threshold voltage of wet-chemical oxidized surface is observed after annealing at 900°C. The C 1s core level by X-ray photoelectron spectroscopy (XPS) showed a shoulder peak at 1eV below the main peak over 800 and 900°C annealing temperature for hydrogen-plasma treated and wet-chemical oxidized surfaces, respectively. When the shoulder peak intensity is less than 10% of the main peak intensity, lower threshold voltages are observed. This is due to the carbon-reconstruction which gives rise to a small positive electron affinity. By increasing annealing temperature, the shoulder peak ratios also increase, which indicates that a surface graphitization takes place. This leads to higher threshold voltages.

Keywords: Field emission; Surface modification; Vacuum annealing; Phosphorus-doped diamond; Electron affinity

Effect of H₂ and O₂ plasma etching treatment on the surface of diamond-like carbon thin film by Deok Yong Yun; Won Seok Choi; Yong Seob Park; Byungyou Hong (pp. 7925-7928).

In this study, we investigated the surface properties of diamond-like carbon (DLC) films for biomedical applications through plasma etching treatment using oxygen (O₂) and hydrogen (H₂) gas. The synthesis and post-plasma etching treatment of DLC films were carried out by 13.56MHz RF plasma enhanced chemical vapor deposition (PECVD) system. In order to characterize the surface of DLC films, they were etched to a thickness of approximately 100nm and were compared with an as-deposited DLC film. We obtained the optimum condition through power variation, at which the etching rate by H₂ and O₂ was 30 and 80nm/min, respectively. The structural and chemical properties of these thin films after the plasma etching treatment were evaluated by Raman and Fourier transform infrared (FT-IR) spectroscopy. In the case of as-deposited and H₂ plasma etching-treated DLC film, the contact angle was 86.4° and 83.7°, respectively, whereas it was reduced to 35.5° in the etching-treated DLC film in O₂ plasma. The surface roughness of plasma etching-treated DLC with H₂ or O₂ was maintained smooth at 0.1nm. These results indicated that the surface of the etching-treated DLC film in O₂ plasma was hydrophilic as well as smooth.

Keywords: PACS; 78.55.Qr; 78.30.−j; 71.55.Jv; 77.84.BwDiamond-like carbon; Plasma etching; Surface treatment; Hydrophilic

Development of the overpotential simulator for polymer electrolyte fuel cells and application for optimization of cathode structure by Tatsuya Hattori; Ai Suzuki; Riadh Sahnoun; Michihisa Koyama; Hideyuki Tsuboi; Nozomu Hatakeyama; Akira Endou; Hiromitsu Takaba; Momoji Kubo; Carlos A. Del Carpio; Akira Miyamoto (pp. 7929-7932).

We developed a novel computational method to investigate the influences of the microstructure of the polymer electrolyte fuel cell cathode catalyst layer on the overpotential characteristic toward its optimization. Three-dimensional cathode catalyst layer models were constructed by applying three-dimensional porous structure simulator and developed simulator was used to study the overpotential characteristics. Our results showed that the overpotential decreased as decrease of the standard deviation of the ionomer thickness distribution due to the increase of number of active sites.

Keywords: PACS; 82.45.Fk; 82.47.Nj; 78.55.Mb; 82.20.WtPolymer electrolyte fuel cell; Cathode; Microstructure; Overpotential; Optimization

Elimination of GeO₂ and Ge₃N₄ interfacial transition regions and defects at n-type Ge interfaces: A pathway for formation of n-MOS devices on Ge substrates by G. Lucovsky; S. Lee; J.P. Long; H. Seo; J. Lüning (pp. 7933-7937).

The contribution from relatively low -K SiON interfacial transition regions (ITRs) between Si and transition metal (TM) gate dielectrics places a significant limitation on equivalent oxide thickness (EOT) scaling for Si complementary metal-oxide-semiconductor (CMOS) devices. This limitation is equally significant and limiting for Ge CMOS devices. Low-K Ge-based ITRs in Ge devices have also been shown to limit performance and reliability, particular for n-MOS field effect transistors. This article identifies the source of significant electron trapping at interfaces between n-Ge or inverted p-Ge, and Ge oxide, nitride and oxynitride ITRs. This is shown to be an interfacial band alignment issue in which native Ge ITRs have conduction band offset energies smaller than those of TM dielectrics, and trap electrons for negative Ge substrate bias. This article also describes a novel remote plasma processing approach for effectively eliminating any significant native Ge ITRs and using a plasma-processing/annealing process sequence for bonding TM gate dielectrics directly to the Ge substrate surface.

Keywords: n-type Ge substrates; Interfacial transition regions; n-MOS devices; Band gaps GeO; ₂; and Ge; ₃; N; ₄; X-ray absorption spectroscopy; Visible and VUV SE

Model Eliashberg functions for surface states by A. Nojima; K. Yamashita; B. Hellsing (pp. 7938-7941).

We present a simplified procedure for the analysis of the phonon-induced lifetimes of surface states. The model includes information about the electron and phonon structure and is thus more reliable than procedures based on phonon Debye models. We apply the model to calculate the lifetime broadening of Cu(111) and Al(001) surface states. The obtained Eliashberg functions and lifetimes are in reasonable agreement with previous detailed studies.

Keywords: PACS; 63.20.Kd; 63.20.Pw; 72.10.Di; 73.20.At; 72.15.Lh; 73.25.+iElectron–phonon coupling; Lifetime broadening; Surface states; Eliashberg function; Rayleigh mode; Metal surface

Atomistic nitriding processes of titanium thin films due to nitrogen-implantation by Y. Kasukabe; S. Nishida; S. Yamamoto; M. Yoshikawa; Y. Fujino (pp. 7942-7946).

Nitrogen ions (N₂⁺) with 62keV were implanted into the as-deposited Ti film composed of mainly (110)-oriented TiH_x and (03·5)-oriented hcp-Ti at room temperature, which results in the epitaxial formation of (110)-oriented and (001)-oriented TiN_y, respectively. The electron energy loss spectroscopy experiments elucidate that in the early N-implanting stage the release of hydrogen constituting TiH_x gives rise to the shift of the loss peak due to plasmon excitation to lower loss energy side. On the other hand, the energy loss peaks due to plasmon excitation for nitriding of hcp-Ti gradually shifted to higher energy side with increasing dose. Through the N-invasion into the octahedral sites of hcp-Ti with larger space and lower electron density, the hcp–fcc transformation of Ti sublattices is induced by the shift of the (00·1)-plane in the01⋅0 direction of hcp-Ti promoted by the forming of the strong Ti–N bonds including the π-type covalent bonds, and by the weakening of the Ti–Ti bonds. Furthermore, the inheritance of square atomic arrangement and the movement of the N atom to other neighboring O-site in the transformed fcc-Ti sublattice are responsible for the epitaxial growth of TiN_y. The atomistic processes of the epitaxial growth of TiN_y are discussed with the aid of the molecular orbital calculations.

Keywords: PACS; 68.37.Lp.; 68.55.Jk.; 81.15.Aa.; 85.40.RyIon-implantation; TiN; fcc–hcp transformation; In situ TEM; EELS

Birefringence measurements of MnPc thin film by polarization microscopy by T. Hashimoto; T. Kaito; S. Yanagiya; A. Mori; N. Goto (pp. 7947-7949).

We have studied optical properties of near-infrared (NIR) spectra and birefringence of the manganese phthalocyanine (MnPc) thin films. The morphology of the MnPc thin film grown on KCl (001) substrates was observed by using an atomic force microscope. The NIR spectral range of 1.0–1.7μm was studied in this study, because that of 1.3–1.5μm is known as an optical communication wavelength. The birefringence was measured with changing the growth condition of a deposition rate and a substrate temperature. The birefringence of the film was most affected by the deposition rate.

Keywords: Manganese-phthalocyanine; KCl; Birefringence

An extreme change in structural and optical properties of indium oxynitride deposited by reactive gas-timing RF magnetron sputtering by A. Sungthong; S. Porntheeraphat; A. Poyai; J. Nukeaw (pp. 7950-7954).

The indium oxynitride (InON) films were achieved by reactive RF magnetron sputtering indium target which has the purity of 99.999% with a novel reactive gas-timing technique. The structural, optical and electrical properties in a series of polycrystalline InON films affected by gas-timing of reactive N₂ and O₂ gases introduced to the chamber were observed. The X-ray photoelectron spectroscopy revealed that the oxygen content in thin films that compounded to indium and nitrogen, which increased from 10% in indium nitride (InN) to 66% in indium oxide (In₂O₃) films. The X-ray diffraction peaks show that the phase of deposited films changes from InN to InON and to In₂O₃ with an increasing oxygen timing. The hexagonal structure of InN films with predominant (002) and (004) orientation was observed when pure nitrogen is only used as sputtering gas, while InON and In₂O₃ seem to demonstrate body-center cubic polycrystalline structures depending on gas-timing. The surface morphologies investigated from atomic force microscope of deposited films with varying gas-timing of O₂:N₂ show indifferent. The numerical algorithm method was used to define the optical bandgap of films from transmittance results. The increasing oxygen gas-timing affects extremely to the change of crystallinity phase from InN to InON and to In₂O₃, the increase of optical bandgap from 1.4 to 3.4eV and the rise of sheet resistance from 15Ω/□ to insulator.

Keywords: PACS; 68; .55.Jk; 68.37.Ps; 61.66.Dk; 61.10.NzIndium nitride; Indium oxynitride; Indium oxide; Reactive gas-timing; RF magnetron sputtering

Development of the reaction time accelerating molecular dynamics method for simulation of chemical reaction by Hiromitsu Takaba; Shigekazu Hayashi; Huifeng Zhong; Hema Malani; Ai Suzuki; Riadh Sahnoun; Michihisa Koyama; Hideyuki Tsuboi; Nozomu Hatakeyama; Akira Endou; Momoji Kubo; Carlos A. Del Carrpio; Akira Miyamoto (pp. 7955-7958).

We present a novel and efficient method to integrate chemical reactions into molecular dynamics to simulate chemical reaction systems. We have dubbed this method RTAMD, an acronym for reaction time accelerating molecular dynamics. The methodology we propose here requires no more than the knowledge of the empirical intermolecular potentials for the species at play as well as the elementary reaction path among them. Bond formation during the simulation is performed by changing the inter-atomic potentials from those of the non-bonded species to those of the bonded ones, and a reaction is deemed to occur by the distance separating the bond forming atoms. In this way the energy barrier for a reaction is no longer considered; the estimation of the reaction rate, however, is possible by introducing the principles of the transition state theory. The simplicity of the present scheme to simulate chemical reactions enables it to be used in large-scale MD simulations involving a large number of simultaneous chemical reactions and to evaluate kinetic parameters. In this paper, the basic theory of the method is presented and application to simple equiatomic reaction system where the reaction rates were estimated was illustrated.

Keywords: PACS; 82.40.−g; 82.39.−k; 83.10.RpChemical reaction; Reaction kinetics; Molecular simulation

Preparation and electrical properties of Cr₂O₃ gate insulator embedded with Fe dot by Takeshi Yokota; Takaaki Kuribayashi; Shotaro Murata; Manabu Gomi (pp. 7959-7962).

We investigated the electrical properties of a metal (Au)/insulator (magneto-electric materials: Cr₂O₃)/magnetic materials (Fe)/tunnel layer (Cr₂O₃)/semiconductor (Si) capacitor. This capacitor shows the typical capacitance–voltage ( C– V) properties of an Si-MIS capacitor with hysteresis depending on the Fe dispersibility which is determined by the deposition condition. The C– V curve of the only sample having a 0.5nm Fe layer was seen to have a hysteresis window with a clockwise trace, indicating that electrons have been injected into the ultra-thin Fe layer. The samples having Fe layers of other thicknesses show a counterclockwise trace, which indicates that the film has mobile ionic charges due to the dispersed Fe. These results indicated that the charge-injection site, which works as a memory, in the Cr₂O₃ can be prepared by Fe insertion, which is deposited using well-controlled conditions. The results also revealed the possibility of an MIS capacitor containing both ferromagnetic materials and an ME insulating layer in a single system.

Keywords: Magneto-electric effect; Dielectric properties; FETs; Capacitance measurement; MIS devices

Molecular beam epitaxy of semiconductor (BaSi₂)/metal (CoSi₂) hybrid structures on Si(111) substrates for photovoltaic application by Y. Ichikawa; M. Kobayashi; M. Sasase; T. Suemasu (pp. 7963-7967).

We have succeeded in growing semiconductor (BaSi₂)/metal (CoSi₂) hybrid structures epitaxially on Si(111) by molecular beam epitaxy for the first time. When the thickness of CoSi₂ was approximately 55nm, the interface between the CoSi₂ and BaSi₂ layers was found to be rough from transmission electron microscopy observation. The interface became sharp and the BaSi₂/CoSi₂ hybrid structures were epitaxially grown when the thickness of CoSi₂ was decreased down to approximately 27nm, and the growth temperature was properly chosen.

Keywords: PACS; 61.10.Nz; 68.37.Lp; 68.35.CtSemiconducting silicide; BaSi; ₂; CoSi; ₂; Molecular beam epitaxy; Interface

Selective-area-growth of InAs-QDs with different absorption wavelengths via developed metal-mask/MBE method for integrated optical devices by N. Ozaki; Y. Takata; S. Ohkouchi; Y. Sugimoto; N. Ikeda; K. Asakawa (pp. 7968-7971).

The selective-area-growth (SAG) of InAs quantum dots (QDs) with different emission wavelengths on different areas was carried out using the metal-mask (MM) method during conventional molecular beam epitaxy (MBE) growth. Two SAG areas (SAG-1 and SAG-2) of the QDs were obtained using the rotational MM having square windows; first, the MM was mounted on a substrate for SAG-1, and then the same MM was used for SAG-2 after being rotated it by 180°. The absorption wavelengths of the selectively grown QDs were controlled by inserting strain-reducing layers of a different thickness on each grown QD layer. Photoluminescence measurements revealed the successful SAG of QDs in the neighboring a few hundred-micron-square areas with different emission wavelengths, e.g., 1250 and 1300nm. These techniques are promising for applications of QD-based optical and electronic devices, including our proposed photonic crystal (PC) and QD-based all-optical digital flip–flop (FF) device, i.e., PC-FF.

Keywords: PACS; 73.21.La; 78.55.Cr; 78.67.Hc; 81.15.Hi; 81.16.DnSelective-area-growth; Quantum dots; Metal-mask; All-optical photonic device; Photonic crystal

Lattice deformation of ZnO films with high nitrogen concentration by S.H. Park; J.H. Chang; H.J. Ko; T. Minegishi; J.S. Park; I.H. Im; M. Ito; D.C. Oh; M.W. Cho; T. Yao (pp. 7972-7975).

Nitrogen-doped ZnO/Al₂O₃ films grown at elevating temperatures (300–800°C) have been investigated by plasma-assisted molecular beam epitaxy (P-MBE). High nitrogen concentration (∼10²²cm⁻³) is achieved in the films grown at relatively low growth temperature (<500°C) range. High nitrogen concentration accompanies considerable degradation of crystallinity and residual tensile strain, which was evaluated by high resolution X-ray diffraction (HRXRD). The structural evolution is discussed in terms of the increase of complex defect density in the films. The ionization energy of acceptor was estimated as ∼140meV from the excitation power dependence of donor–acceptor pair emission line by using low temperature (10K) photoluminescence spectroscopy.

Keywords: PACS; 34.35.+aNitrogen incorporation; ZnO; Lattice strain

A theoretical investigation on the abrasive wear prevention mechanism of ZDDP and ZP tribofilms by Tasuku Onodera; Yusuke Morita; Ai Suzuki; Riadh Sahnoun; Michihisa Koyama; Hideyuki Tsuboi; Nozomu Hatakeyama; Akira Endou; Hiromitsu Takaba; Momoji Kubo; Carlos A. Del Carpio; Clotilde Minfray; Jean-Michel Martin; Akira Miyamoto (pp. 7976-7979).

We investigated wear prevention mechanism of tribofilms generated from zinc dialkyldithiophosphate (ZDDP) and zinc dialkylphosphate (ZP) anti-wear additive using molecular dynamics simulations. The friction behavior of two model materials, zinc metathiophosphate and zinc metaphosphate, was studied. The results indicated that zinc metathiophosphate prevents the abrasive wear due to the atomistic digestion of the wear particles in the tribofilm. We also investigated wear prevention mechanism of zinc metaphosphate and found that it has a better wear prevention performance than zinc metathiophosphate as far as abrasive wear is concerned. Our study showed that zinc metaphosphate can achieve good wear prevention and reduce the environmental load since it does not contain sulfur.

Keywords: PACS; 31.15.Qg; 46.55.+d; 81.05.Pj; 81.40.PqMolecular dynamics simulation; ZDDP; ZP; Abrasive wear; Wear particle

Direct observation of deformation of nafion surfaces induced by methanol treatment by using atomic force microscopy by Kazuo Umemura; Reiko Kuroda; Yanfeng Gao; Masayuki Nagai; Yuta Maeda (pp. 7980-7984).

We successfully characterized the effect of methanol treatment on the nanoscopic structures of a nafion film, which is widely used in direct methanol fuel cells (DMFCs). Atomic force microscopy (AFM) was used to repetitively image a particular region of a nafion sample before and after methanol solutions were dropped onto the nafion film and dried in air. When the surface was treated with 20% methanol for 5min, many nanopores appeared on the surface. The number of nanopores increased when the sample was treated twice or thrice. By repetitive AFM imaging of a particular region of the same sample, we found that the shapes of the nanopores were deformed by the repeated methanol treatment, although the size of the nanopores had not significantly changed. The creation of the nanopores was affected by the concentration of methanol. Our results directly visualized the effects of methanol treatment on the surface structures of a nafion film at nanoscale levels for the first time.

Keywords: Nafion; Atomic force microscope; Nanolithography; Methanol

Transport properties of iron–porphyrin molecule sandwiched between Au surfaces by Hisashi Kondo; Hiori Kino; Jun Nara; Takahisa Ohno (pp. 7985-7988).

The transport properties of an iron–porphyrin molecule sandwiched between Au(111) electrodes are investigated using the non-equilibrium Green’s function method based on the density functional theory, and in particular, the dependence on a terminal-atom position is studied. We consider four models for terminal-atom positions. It is found that the transport properties of the junction system are very sensitive to a terminal-atom position. We also find that the contribution of the d-orbitals of the Fe atom to the transport properties around the Fermi energy strongly changes, depending on a terminal-atom position. From these results, we propose a suitable terminal-atom position for the molecular sensor discussed in the other paper.

Keywords: PACS; 73.63.; −; b; 85.65.+hIron–porphyrin; Molecular sensor; Nano-device; Transport properties

Behavior of the reemitted slow positron on hydrogen-adsorbed Ni (111) surface by K. Hirota; S. Komagata; S. Arii; I. Kanazawa; K. Fukutani; K. Nozawa; F. Komori (pp. 7989-7992).

We have analyzed the Doppler broadening spectra of the positron annihilation and reemitted slow positrons from hydrogen-adsorbed Ni (111) surface on different adsorbing conditions. It is shown that the escaping of reemitted slow positrons and ortho-positroniums from hydrogen-lightly adsorbed Ni (111) is more than that of hydrogen-saturatedly adsorbed Ni (111).

Keywords: PACS; 34.50.Dy; 68.49.−h; 34.85+xAdsorbed hydrogen; Ni surface; Reemitted slow positron; Positron annihilation

Cr doping in Zn1−_xCr_xO crystals beyond the solubility limit by the catalytic electric current heating method by K. Shimoda; T. Yasui; Y. Kuroki; M. Takata (pp. 7993-7995).

We have developed the simple method enables Zn1−_xCr_xO crystals to form with variation in Cr composition ratio. Energy-dispersion X-Ray spectroscopy indicated that the pre-deposited Au catalyst promoted the growth of Zn1−_xCr_xO crystals on a sapphire (0001) substrate. Whiskers and particles coexisted as the Zn1−_xCr_xO crystals up to 7% of Cr composition, in contrast, those particles grew above 7%. It has been found that the lattice constant of Zn1−_xCr_xO decreased as the Cr composition up to 7%. A Cr content of 7% in the sublimation source corresponds to the Cr composition of 9.2% in Zn1−_xCr_xO crystal. This research has successfully enable Cr doping beyond solubility limit in Zn1−_xCr_xO crystals.

Keywords: PACS; 68.70+w; 81.07.−b; 81.16.HcZn; 1−; _x; Cr; _x; O crystals; Catalytic growth; Catalytic electric current heating method

Detection of sulfur from Ni(110) surface using by electron-stimulated desorption spectroscopy by Kazuyuki Ueda; Takeshi Yagami (pp. 7996-7998).

On the Ni(110) surface, H⁺ and O⁺ are normally detected by electron-stimulated desorption (ESD). However, C⁺, N⁺, S⁺ are normally insensitive to ESD measurement. In this report S⁺ signal has been significantly detected by the ESD from the Ni(110) surface. Behavior of S⁺ has been observed in the variation of time-of-flight (TOF)–ESD spectra during heating.

Keywords: Sulfur; Ni(1; 1; 0); Electron-simulated desorption; ESD

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Applied Surface Science (v.254, #23)