Optical transmittances of the hydrated Ag-4A zeolite were measured under vacuum at elevated temperatures. Optical transmittance measurements reveal that there are two stages of the creation of the Ag cluster under 80 °C. The evacuation below 50 °C induces the absorption above 2.2 eV. The evacuation above 60 °C brings about the new peak at 2.8 eV which peak is origin of yellow color. [DOI: 10.1380/ejssnt.2005.270]

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Indium tin oxide (ITO) thin films were deposited on polyethylene terephthalate (PET) substrates at room temperature by RF magnetron sputtering with a new technique, called gas-timing. The influence of RF power on properties of ITO thin films was investigated. From the x-ray diffraction measurement of the ITO thin films grown by this technique, cubic nano-crystalline structure with predominant (222) and (400) orientation was observed. It was found that the increasing of RF power yielded to decrease in the sheet resistance of ITO thin films. The sheet resistance of ITO thin films deposited by RF power of 40 watts had the lowest value of 8 Ω/Square. By the gas-timing technique, the ITO thin films on PET substrates were achieved with high transmittance in visible region of 90%. Therefore, the gas-timing RF magnetron sputtering is a promising technique to achieve the ITO thin film on PET substrate with low resistivity and high transmittance in visible region without substrate heating and post-deposition annealing. [DOI: 10.1380/ejssnt.2005.272]

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We prepared a series of substrates with various roughness, on which we deposited the thin films of c-axis oriented La_2-xBa_xCuO₄ copper oxide superconductor with x fixed at the optimum doping 0.15 under common and reproducible conditions using pulsed laser deposition. By measuring the substrate surface roughness on the terrace with atomic force microscopy and the superconducting transition temperature T_c with the in-plane resistivity measurement, we investigated the correlation between T_c and terrace roughness on the substrate surface. We observed a tendency that those deposited on substrates with smoother terrace show higher T_c. Possible reasons of this correlation is discussed. [DOI: 10.1380/ejssnt.2005.276]

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We have established a process to fabricate Ag nanorod arrays with tunable morphology, hence tunable plasmonic properties. Based on a dynamic oblique deposition (DOD) technique, the nanorods are aligned in a way where their major axis is quasi-parallel. The aspect ratio of the nanorods is adjusted by choosing an appropriate DOD condition to show plasma resonance in the wavelength region around the Raman scattering at the excitation wavelength of 785 nm. The nanorod arrays thus tuned provide intense surface enhanced Raman scattering useful for practical applications to biochemical sensors. [DOI: 10.1380/ejssnt.2005.280]

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Under ultraviolet (UV) irradiation, an ultra thin titanium native oxides film covered by a hydrocarbon contamination (HC) layer on the as-deposited titanium film was investigated by using spectroscopic ellipsometry (SE), atomic force microscopy (AFM) and contact angle meter. Using a stable silicon dioxide sample as a reference provided an insight of the structural change of the titanium native oxide film under UV irradiation. The SE results indicate that UV irradiation can completely remove the adsorbed HC layer both on the Ti sample and on Si sample after 337 min and 4059 min respectively. The titanium native oxide accelerates the HC removing process. The pseudo-optical constants (pseudo-n and pseudo-k) of the Ti composite and the thickness of the surface layer on Ti decreased during UV irradiation, which was considered to be contributed to the changes of the surface properties of the titanium composite film. AFM images on the surface of UV-treated titanium native oxide films present a less root-mean-square (RMS) roughness and many isolated gains with a size of about 10 nm. [DOI: 10.1380/ejssnt.2005.284]

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The electrochemical reduction of 4-nitrobenzene diazonium salt has been investigated at carbon electrodes. Glassy carbon and pyrolyzed photoresist films were used as substrates to examine the attached nitrophenyl (NP) thin films using electrochemistry and atomic force microscopy (AFM). NP-films were treated to negative potential excursions in aqueous acidic conditions to electrochemically reduce the NP groups. The voltammetric responses of Fe(CN)_{6}^{3-} redox probe were recorded, and the film thicknesses monitored by an AFM mechanical scratching method that involves removing a section of the film with an AFM tip and measuring the depth profile of the trench created. A mechanism is proposed to account for the observed film changes. [DOI: 10.1380/ejssnt.2005.294]

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The geometric and electronic properties of alkali metals (Na and Cs) on ZnO(10-10) are investigated by means of photoelectron spectroscopy and low energy electron diffraction (LEED). Growth of the Na overlayer on ZnO(10-10) at room temperature is characterized by layer-by-layer growth or monolayer growth followed by three-dimensional cluster growth. The Na adatoms in the first layer are in a cationic state, and the metallic phase is formed on top of the first cationic layer. Although Na deposition at room temperature does not yield any long-range ordered superstructure, annealing the Na-covered surface results in a (1×3) LEED pattern, and we propose the formation of the Na atomic chains along the Zn--O dimer rows. For the Cs adsorption system, the disordered overlayer by ionized Cs adatoms is also formed throughout the submonolayer coverage region. Unlike the Na adsorption system, heat treatment of the Cs-covered surface does not yield any ordered structure until all Cs adatoms desorb from the surface. [DOI: 10.1380/ejssnt.2005.299]

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TiO₂-SiC was prepared by oxidization of TiC-SiC precursor which was obtained by carbothermic reduction process of TiO₂-SiO₂. XRD analysis indicated the formation of the mixture of anatase and rutile phases of TiO₂ crystalline after the oxidation of TiC-SiC sample. TiO₂-SiC photocatalyst exhibited the higher photocatalytic reactivity than TiO₂ loaded on SiO₂ (TiO₂-SiO₂) prepared by the conventional sol-gel method and commercial TiO₂ powder (P-25). These results indicated the advantages of SiC powders as catalyst support of the TiO₂ photocatalyst. [DOI: 10.1380/ejssnt.2005.311]

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Basic H₂ gas-sensing characteristics of Pd Schottky diodes formed on the AlGaN/GaN heterostructure were investigated in vacuum. By introducing a novel surface control process to reduce reverse leakage currents, an unprecedented high H₂ sensitivity was achieved where 1 Torr hydrogen caused five orders of magnitude change of current. Surprisingly, the surface control process did not change the C-V characteristics which showed an unexpectedly large shift 1000 mV on H₂ exposure. Transient waveforms were almost exponential for the logarithm of current, and response speed increased with increase of H₂ pressure and temperature. These results were explained in terms of Schottky barrier height due to adsorption of atomic hydrogen generated by Pd together with a due consideration of the current transport mechanism under reverse bias. [DOI: 10.1380/ejssnt.2005.314]

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Observations of the crystallographic structural changes of deposited Ti films (100 nm thick) during C-implantation were made by using transmission electron microscope (TEM) for the purpose to elucidate the carbonizing processes of Ti films. The Ti films were deposited by an electron beam heating method onto thermally cleaned NaCl (001) surfaces held at room temperature (RT). Both the 200 kV conventional TEM and the 400 kV analytical high resolution TEM combined with ion accelerators were used. The deposited Ti films consisted of mainly (03\\cdot 5)-oriented hcp-Ti and (110)-oriented CaF₂ type TiH_x (x ∼ 1.5). Carbon ions (C⁺) with 26 keV were implanted into the Ti films held at RT in the 400 kV TEM. The H atoms which constituted TiH_x were released from the as-deposited Ti films during the early stage of C-implantation. In the C-implanted Ti film (C/Ti=0.54), there coexisted (001)- and (110)- oriented NaCl-type TiC_y and a small amount of hcp-Ti. The results of TEM observation indicated that (001)- and (110)-oriented TiC_y were epitaxially formed by the transformation of (03\\cdot 5)-oriented hcp-Ti and (110)-oriented TiH_x, respectively. In the cases, the hcp-Ti sublattice is transformed into fcc-Ti sublattice of TiC_y with inheritance of square atomic arrangement of hcp-Ti. The hcp-fcc transformation was discussed with the results of a self-consistent charge discrete variational (DV)-Xα molecular orbital (MO) calculation. [DOI: 10.1380/ejssnt.2005.319]

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Organic static induction transistors (SITs) with nano-hole arrays in a lateral direction was fabricated using a 'colloidal lithography' technique. Positively charged polystyrene particles of 200 nm diameter as a deposition mask were adsorbed on a glass surface via electrostatic self assembly. A source electrode, a bottom CuPc layer, and a Schottky gate electrode were deposited succeedingly on the particle-adsorbed glass substrate. After the particles were removed, a large number of nano-holes were formed without destroying the films. A top CuPc layer and a top drain electrode were deposited on the nano-hole layers to complete the SIT, where the nano-holes work in parallel as active conducting channels. The obtained SIT characteristics showed that the source-drain current is modulated by a positive gate bias. [DOI: 10.1380/ejssnt.2005.327]

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For ultra-high-density integration of gate-controlled quantum devices, one possible phenomenon limiting the ultimate integration density is a side-gating effect which has not been properly addressed so far for nanodevices. The purpose of this paper is to attempt to remove the side-gating effect from the GaAs quantum wire transistors where we recently have found presence of anomalously large side-gating effect. We first present data on the side-gating and we explain its mechanism in terms of tunneling injection of electrons by field concentration at gate edges caused by Fermi level pinning. Then, we apply our Si interface control layer (Si ICL) passivation process to reduce the pinning. By applying the Si ICL technique via thin GaAs cap layer, the anomalously large side-gating was completely suppressed, and only electrostatic side-gating theoretically expected from the device structure remained. [DOI: 10.1380/ejssnt.2005.332]

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¹²⁹Xe NMR spectroscopy is applied to investigate the physical properties of Xe confined in porous glasses up to the supercritical region. The chemical shift of confined Xe is larger than that of bulk Xe, which is approximately proportional to density, and the upward deviation is more enhanced for smaller pore. The deviation is large in the gas phase, and has a maximum far below the critical density, while it gradually decreases and approaches zero in the liquid phase. Below the critical density the both of the size and surface effects are observed, while the surface effect becomes minor and the size effect persists above the critical density. The chemical shift at the dilute limit depends on the surface properties of the matrix, as well as the pore size. [DOI: 10.1380/ejssnt.2005.338]

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Organic light-emitting diodes (OLEDs) were fabricated using polymer;Poly(N-vinylcarbazole);(PVK) films, electron transport material;2-(4-Biphenylyl)-5-(4-tert-butyl-phenyl)-1,3,4-oxadiazole ;(PBD) as the host material and Nile Red as the dopant emission material. Organic layers were prepared by spin-coating the solution of CHCl₃ on the indium-tin-oxide(ITO) coated glasses. The effects of inserting poly(styrenesulfonate)/poly(2,3-dihydrothieno(3,4-b)-1,4dioxin) (PEDOT-PSS) layer between ITO and organic layer on the characteristics of OLEDs with Nile Red were investigated. EL spectra have two main peaks at near 430 nm and 590 nm. By inserting PEDOT-PSS layer, the emission of the peak at 430 nm increased and that of the peak at 590 nm decreased. [DOI: 10.1380/ejssnt.2005.341]

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Polarization curve of titanium was measured in sulfuric acid solution. Titanium films were treated at different electrochemical potentials and then were investigated by means of spectroscopic ellipsometry. The thickness of anodized films decreased in air within 280 min over 500 mV vs. Ag/AgCl. The parameters tan Ψ and cos Δ in spectroscopic ellipsometry were in a good agreement with the polarization curve and the thickness of anodized films respectively. Due to the density decrease of anodized titanium films, that was to say, the change to a more porous structure, both the refractive index and the extinction coefficient of the composite film of anodized film and titanium substrate decreased with the increase of the treated potentials at a fixed wavelength over 350 nm. [DOI: 10.1380/ejssnt.2005.345]

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Dynamic surface structures of Tin (Sn) on Si(111) were studied by using low energy electron microscope (LEEM). Different from the reported phase diagram, (√3 × √3)-R 30° Sn structure is found existing only in a narrow Sn film thickness range and disappearing quickly over 1/3 monolayer (ML) Sn deposition at substrate temperature of 400°C. Sn islands, which are different from the S-K mode growth, begin to grow from around 1/5 ML along steps or domain boundaries. The models of Sn growth on Si(111) are proposed. [DOI: 10.1380/ejssnt.2005.350]

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Spin-polarized X-ray photoelectron diffraction (SPXPD) spectra are useful to study magnetic structures of solid surfaces. In this work two different SPXPD modes are studied on the basis of a relativistic quantum electrodynamic (QED) theory which provides a unified picture of the SPXPD analyses. An important advantage of this theory is to allow us to handle many-body relativistic XPS theory, which can be a basis of SPXPD analyses. One mode is to utilize the spin polarization caused by multiplet splittings as observed in O₂ molecules and Gd metals. We demonstrate how to extract local magnetic order in surface O₂ . The second SPXPD mode is to use circularly polarized X-rays to discriminate the spin polarization with aid of spin-orbit coupling. [DOI: 10.1380/ejssnt.2005.353]

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The density functional theory is applied to study energetics of lithium ion adsorption on single-wall carbon nanotubes (SWNTs). We use both the local density approximation (LDA) and the generalized gradient approximation (GGA) for the exchange-correlation energy functional. The formation energies of the n 7, 8, and 9 defective rings are calculated and their stable geometries are examined. We also estimate the lithium adsorption energies for these defective rings and the efficiency of the lithium ion battery with the defective SWNTs as the negative electrode. [DOI: 10.1380/ejssnt.2005.358]

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We have measured electrical resistance of individual epitaxial CoSi₂ nanowires (NWs) formed on a Si(110) surface in situ in ultrahigh vacuum, by two-, three-, and four-point probe methods using a multi-tip scanning tunneling microscope at room temperature. The NWs were electrically isolated from the substrate by a Schottky barrier in-between with zero-bias resistance of approximately 10⁷ Ω. Contact resistance between a W tip and a NW was as small as several tens Ω. The resistivity of the NWs was ca. 30 μΩcm, which is similar to that of high-quality epitaxial CoSi₂ films. The oxidation of the NW surface had negligible influence on the resistance, meaning marginal carrier scattering at the NW surface. [DOI: 10.1380/ejssnt.2005.362]

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We have newly developed an inverse photoemission (IPE) spectrometer with high efficiency and measured k-resolved IPE spectra of LaB₆(001) to study the unoccupied surface states. The surface states were found to be located at 0.2 eV above the Fermi level at the Γ point and showed energy dispersion along the Γ–M direction of the surface Brillouin zone (BZ). The dispersion of the unoccupied surface states is inconsistent with the recently reported theoretical calculation. The discrepancy is considered that the calculation adopted smaller interlayer spacing between topmost La layer and B subsurface as it is in the system. [DOI: 10.1380/ejssnt.2005.367]

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Extended X-ray absorption fine structure (EXAFS) measurements were carried out in order to investigate the phase transition of bismuth clusters from semi-metallic nanocrystal to semiconducting amorphousness depending on the size. XAFS functions were Fourier-transformed and analyzed by the curve fitting method. The peaks around 3.0 Å and 3.6 Å are attributed to the nearest neighbors within the the layer and between the interlayer, respectively. In the 0.5 nm thick films the covalent bond length within the layer slightly shortens and the peak originated from the interlayer disappears. [DOI: 10.1380/ejssnt.2005.370]

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The angular distribution of emitted photoelectrons is theoretically studied for high-energy X-rays where electric quadrupole and magnetic dipole transitions are taken into account in addition to the electric dipole transition. We apply irreducible tensor expansion of photon field instead of usual power series expansion. The present numerical calculations show that the conventional power series expansion works so well up to quite high energy for the core excitation. We also discuss the recoil effects of nuclei associated with photoemission excited by high-energy X-rays, which gives rise to the energy shift and the peak broadening. For practical calculation we furthermore introduce Debye approximation for phonon spectra, which brings about the simple free atom recoil energy shift. In the simple Debye approximation we can expect no contribution to the broadening. [DOI: 10.1380/ejssnt.2005.373]

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The evolution of Ga adsorption on a Si(113) surface at sample temperatures between 460°C and 500°C has been investigated using in-situ low-energy electron microscopy and low-energy electron diffraction. The formation of surface facets in the [1-10] direction was observed. From series of low-energy electron diffraction images at different electron energies, reciprocal space maps in different k_⊥-k_// planes were obtained. This allowed to determine both facet angles to be 9.8° ± 1.0° and thus the facet orientations to be (112) and (115). With low-energy electron microscopy, a well ordered array of nanofacets with about 40 nm periodicity in the [33-2] direction was observed. [DOI: 10.1380/ejssnt.2005.379]

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It seems that only the atomic force microscope (AFM) has a potential to trace a protein in action with high spatial and temporal resolution. To realize that potential, we have been developing a high-speed AFM. We have made efforts not only to enhance the scan speed but also to reduce the tip-sample interaction force as much as possible. The high-speed AFM can capture moving protein molecules and weakly interacting protein molecules on video without disturbing their physiological function. Here we review our studies carried out over the past 10 years, and our preliminary work toward the next generation of the instrument. [DOI: 10.1380/ejssnt.2005.384]

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Electrochemical single nucleotide polymorphisms (SNPs) detection was investigated on gold surface modified with 16-base-pair duplex DNAs. In these duplexes, probe DNAs consisted of complementary sequences for target DNAs and a series of ferrocene-diamidopyridine conjugates as an electrochemically active moiety. Regardless of isomeric structures in the conjugates, all the DNA probes showed electrochemical discrimination between fully matched DNAs and SNPs. A detailed comparison was carried out for these probes. [DOI: 10.1380/ejssnt.2005.393]

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Among various lattices, the Kagomé lattice is special because it has a completely flat electronic band whose eigenstates have both localized and itinerant characters. We investigate electron transport properties of finite-size Kagomé-lattice-chain systems, which have multi-degenerate flat-band-like states, using a simple tight-binding model and a nonequilibrium Green function method. It is found that the flat-band-like-state channel in a Kagomé-lattice-chain system generates a large electronic current along the chain when a small electric field is applied perpendicular to the chain, while no current is generated along the chain when an electric field is applied along the chain. We show that such unique transport characteristics originate from the symmetry breaking of flat-band-like states by the external electric fields. [DOI: 10.1380/ejssnt.2005.399]

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Bimodal (meso/macro) porous alumina materials were synthesized using yeast cells as bio-templates. Aluminium isopropoxide (AIP) modified with triethanolamine (TEA) was first hydrolyzed by water containing the dispersed yeast cells. This resulted in the formation of slurry consisting of hydrolyzed sol and yeast cells. After centrifuging the solution, the obtained cake which is packed with hydrated sol and yeast cells was subjected to heat treatment. The sample after heat treatment contained finely dispersed bimodal (meso/ macro) pores ranging in size from 1.5 to 2.0 μm and several nm. Under the present experimental conditions, the thickness of alumina wall was also controlled by changing the ratio of yeast cells to AIP. It was also observed that with an increase in the thickness of the wall, the size of the pores decreased. [DOI: 10.1380/ejssnt.2005.405]

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We report emission properties of single-atom tips, noble electron sources terminated with a single atom. The repairing function of the sources, which had been already demonstrated by using field ion microscope [Fu, et al. Phys. Rev. B 64, 113401 (2001)], was confirmed by using field emission microscopy, and in addition, the demountable character was demonstrated repeatedly. The brightness of the collimated beam emitted from the single-atom tips was estimated to be an order of 10¹⁰ A/cm²/str. (E ∼ 2 keV), which is two orders of magnitude higher than those of the conventional field emission sources. There appeared an extra shoulder in the energy spectra, which is strongly correlated with a single-atom ended structure. The fluctuation of the emission current exhibited step- and spike-like noises, which were typical features of nano-electron sources. The single-atom sources are promising candidates of the electron sources in high-performance electron-beam instruments. [DOI: 10.1380/ejssnt.2005.412]

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We demonstrated the coating of carbon nanotubes (CNTs) with compound ultrathin films towards functional SPM tips. Conductive, ferromagnetic, and uperconducing materials were uniformly coated around isolated multi-walled CNTs (MWNTs). As a conductive probe, the CNT glued on a W tip was wholly coated with a thin PtIr layer 6 nm thick. The current-voltage characteristics of the resultant PtIr-coated CNT tips indicated that the PtIr coating stably reduced the resistance between the CNT tip end and the W supporting tip. Our method will facilitate the development of family of novel functional scanning probe microscopies (SPMs) using CNT tips. [DOI: 10.1380/ejssnt.2005.417]

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DLC (Diamond Like Carbon) attracts attention as a metal surface modification. The amorphous substance of carbon contributes the flatness and low friction-related on the metal surface. The plastic product with thinning wall and light weighting need bigger mold release force than the ordinary product at the mold opening and ejection. Reducing the mold release force by the mold surface modification makes constant and stable production. Surface modification technology based on the metallic material especially DLC is one of the solutions. We studied the friction coefficient between DLC and PMMA resin under different temperatures and inspected the surface characteristics by SPM (Scanning Prove Microscope) from microscopic viewpoint. As the result of surface inspection by the three dimensional roughness comparisons, DLC did not have the directionality and sharp edges on the substance. Such characteristics restrain the deformation force and adhesion force when the PMMA resin slides on the metal surface. Surface modification technology by DLC contributed to reduce the actual mold opening force of the injection molding. [DOI: 10.1380/ejssnt.2005.421]

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We carry out Ni K-edge X-ray Absorption Near Edge Structure (XANES) analyses to study local electronic and geometric structure around Ni impurities after HCl treatment in carbon nanotubes (CNTs) by applying full multiple scattering calculations. For the trace Ni species in CNT after the treatment, we consider possible models consistent with Ni-C distance and coordination number estimated by previous Extended X-ray Absorption Fine Structure (EXAFS) analyses. The present analyses allow us to distinguish between two defect models for the Ni location; a crack-like defect and Stone-Wales defect. We also find that the curvature of CNTs affects the calculated XANES spectra, which can provide useful information about outer or inner adsorption on CNT walls. Ab initio density functional calculation supports the presence of Ni atoms at the outside of the nanotube. [DOI: 10.1380/ejssnt.2005.427]

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Gate leakage currents in AlGaN/GaN HFETs were investigated by comparing experiments with computer simulations based on the thin surface barrier (TSB) model involving unintentional surface donors. Leakage currents in large area Schottky diodes were explained by the TSB model involving nitrogen vacancy related deep donors and oxygen shallow donors. On the other hand, in AlGaN/GaN HFETs with nanometer scale Schottky gates, gate leakage currents include an additional leakage component due to lateral electron injection through tunneling at the gate edge where the barrier thinning is mainly controlled by oxygen donors. By combining vertical and lateral tunneling components, experiments could be reproduced on computer. Lateral components may be responsible for current collapse. [DOI: 10.1380/ejssnt.2005.433]

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Photoabsorption spectra of graphitic ribbons (GR) and triangular graphitic flakes (TGF) are investigated by time-dependent density-functional theory calculations within a real-time scheme. Major peaks in the low-energy region of the spectra are attributed to the π-π^* electronic transitions. The peak of the strength function appears at 3.0 eV owing to π-π^* transitions via edge states for a TGF with hydrogen (H) termination and at 6.0 eV owing to π-π^* transitions at the Γ point for GR with H termination. Small structures in the strength function emerge at 0 ∼ 2 eV for both graphitic structures after extraction of H atoms. The new structures are found to originate from the electronic transitions between dangling-bond states. Thus, the present study shows that the electronic states unique to nanoscale graphitic structures can be captured in the optical absorption spectra. [DOI: 10.1380/ejssnt.2005.439]

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We report ultraviolet photoelectron spectroscopy (UPS) measurements of cyanine dye films fabricated by solution jet beam method without exposure to air. The solution jet beam method is a novel technique to fabricate organic thin films in vacuum, where solution of the organic material is sprayed in vacuum. This method can be applied to organic materials which cannot be vacuum-evaporated due to thermal decomposition, as in the case of cyanine dyes. The observed spectra were sharper than those of spin-coated films exposed to air, demonstrating the advantage of the present approach. The spectra were compared with the results of density functional theory (DFT) calculations. [DOI: 10.1380/ejssnt.2005.444]

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Using a photo-assisted deposition method, a tetrahedrally coordinated chromium oxide moieties (tetra-Cr oxide) can be anchored on a tetrahedrally coordinated titanium oxide moieties (tetra-Ti oxide) included within a framework of mesoporous silica. Under UV-light irradiation, the tetra-Cr oxide moieties can be deposited on the photo-excited tetra-Ti oxide moieties forming a direct interaction. This catalyst can demonstrate as a photocatalyst having the high efficiency and the high selectivity in the photoepoxidation of propene with O₂ under visible light irradiation. [DOI: 10.1380/ejssnt.2005.448]

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We propose a method for investigating the field-effect doping and the capacitance in nano-scale systems by first-principles calculations. Utilizing this method, we demonstrated the field-effect doping into the water bi-layer (channel) sandwiched by a pair of gate electrodes. We found that the H₂O molecules rotated around the O atoms artificially pinned, accompanied by the bias application between the channel and gate electrodes. We confirmed that Q-μ relation (capacitance) was also modified through this rotation of the molecule. We believe that this kind of bias-induced structural modifications of the channel materials can be utilized for designing nano-electronic devices with a variety of novel and functional characteristics. [DOI: 10.1380/ejssnt.2005.453]

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We perform time-dependent (TD) and scattering-state (SS) ab-inito calculations for simulating the field emission (FE) of Na surfaces to explore the applicability of the two schemes. The amplitude of emission current is evaluated more reliably by SS than TD methods, because the former treats the steady-state electron tunneling faithfully but the latter utilizes transient electron dynamics. In contrast with the evaluation of current amplitude, the TD method is more suitable than the SS one for revealing the electronic-state origin of FE, because the TD method can directly determine the time evolution of all wave functions caused by an electric field. Thus, the TD and SS methods are found to play a complementary role in the FE study. [DOI: 10.1380/ejssnt.2005.457]

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Angular dependence of ultraviolet photoelectron spectroscopy (UPS) has been discussed here by using a multiple-scattering theory and has been applied to some large organic molecules. Low kinetic energy electron (<∼50eV) relatively have long mean free path. Moreover the electron-atom scattering shows isotropic scattering features. In order to analyze the local electronic and geometric structure for thin film of large organic molecules by UPS, we should consider the multiple-scattering processes of the photoelectron. In this paper, convergence features of calculated spectra have been discussed by considering scattering order analysis for the calculation of UPS for large organic molecules. Because carbon atoms in organic molecules are weak scatterers, we can neglect high order intramolecular scattering processes. However, the theoretical calculations show that we need careful consideration for near the photoemission threshold energy and for the analysis of large molecule. [DOI: 10.1380/ejssnt.2005.461]

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Our previous quantum electrodynamic (QED) Keldysh Green's function approach provides sound theoretical basis to study the radiation field screening and microscopic photon scatterings. As an application, we derive a useful formula to study low energy photoemission from extended states which incorporates the radiation field screening. This formula can describe the singular behaviors excited by photons with near plasmon energy, and is in particular suitable for the analyses of the photoemission from organic solids because it is written in terms of bond orders and effective charges on each site. [DOI: 10.1380/ejssnt.2005.466]

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Structural transformations occurring spontaneously in a single molecule of sashlike polydiacetylene (PD) -atomic sash (AS)-, obtained by the tip-induced polymerization of a column of 17,19-hexatriacontadiyne (HTDY) molecules laid flat on a graphite (0001) surface, were observed by scanning tunneling microscopy (STM) at room temperature. In the STM images, the AS molecules at first displayed bright contrast due to PD chains lifted-up with twisted alkyl chains at α- and β- methylenes. Soon after the polymerization, paled regions appeared in the AS molecules. The PD chains of these regions seemed snaking and the interval of the alkyl chains was shortened compared with that of the rest of the molecule. The structural change was occasionally accompanied with the alteration of the direction of the PD chains and the rearrangement of the monomer columns around the AS molecules. [DOI: 10.1380/ejssnt.2005.470]

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Deposited Ti films and TiN films formed by nitrogen-implantation were investigated by transmission electron microscope (TEM) observation and electron energy loss spectroscopy (EELS). Titanium films in the thickness of 100 nm were deposited by an electron beam heating method onto thermally cleaned NaCl(001) surfaces held at room temperature under ultra-high vacuum. In the deposited Ti films, there coexist mainly (03 · 5)-oriented hcp-Ti and (110)-oriented TiH_x crystallites: the hydrogen atoms are originally contained in NaCl substrates. The (03 · 5)-oriented hcp-Ti grows inheriting the fourfold symmetry of the square atomic arrangement of TiH_x grown in the early deposition stage. On the other hand, the (110)-oriented TiH_x nucleates and grows naturally inheriting the rectangle atomic arrangement of the (03 · 5)-oriented hcp-Ti to form the band-like region. The deposited Ti films were implanted by N₂⁺ ions with 62 keV in the 400 kV analytical high resolution TEM combined with ion accelerators. In the N-implanted Ti film, the (001)-oriented TiN_y and (110)-oriented TiN_y crystallites are formed outside and inside the band-like regions, respectively. The (110)-oriented TiN_y is formed by nitriding the (110)-oriented TiH_x in the as-deposited Ti film, whereas the (001)-oriented TiN_y is epitaxially formed by the transformation of the (03 · 5)-oriented hcp-Ti to (001)-oriented fcc-Ti, partially inheriting the atomic arrangement of the square and/or the octahedron of the hcp-Ti, accompanied by the occupation of O-sites of the fcc-Ti sublattice by N atoms. In these transformations, the inheritances of the local atomic arrangement of Ti sublattices play a prominent role in the epitaxial fcc-hcp and hcp-fcc formations of the Ti sublattices. The epitaxial formation mechanisms of deposited Ti films and N-implanted Ti films are discussed. [DOI: 10.1380/ejssnt.2005.476]

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Terephthalic acid disodium salt (TADS), C₆H₄(COONa)₂, pyrolyzes in a solid phase at above 600°C. That pyrolysis produces a composite of carbon nanofibrils and fine sodium carbonate crystals. The carbon nanofibrils are amorphous and have 10-200 nm diameter. Forms of the carbon nanofibrils depend on experimental conditions. The carbon fibrils formed at 600°C are slightly entangled and bunched into bundles. Moreover, those bundles are aligned roughly in the direction parallel to the b-axis of the pristine TADS crystals. Wide-angle x-ray diffraction images of a pyrolytic product from a TADS crystal showed those arcs attributable to monoclinic sodium carbonate, indicating the rough alignment of the sodium carbonate crystals. Carbon nanofibrils are inferred to form as a result of exclusion by roughly aligned sodium carbonate crystals. [DOI: 10.1380/ejssnt.2005.484]

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Surface phase diagram of GaAs(001) is systematically investigated by using our ab initio-based approach. The phase diagrams of the c(4 × 4) and (2 × 4) surfaces are clarified as functions of temperature and As pressure. The calculated results reveal that c(4 × 4)β and (2 × 4)γ surfaces are strongly affected by As-molecular species such as As₂ and As₄. The c(4 × 4)β surface consisting of As dimers disappears under As₄ because of small desorption energy of As dimers. The (2 × 4)γ surface appears only at high As pressure and low temperatures buried in the stable region of c(4 × 4)β under As₄. These results are compared with experimental results to check the versatility of our approach to the surface phase diagram calculations. [DOI: 10.1380/ejssnt.2005.488]

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We conducted Monte Carlo simulation for a Li system adsorbed on a Cu(001) surface at various coverage of adatoms, σ >1/2, σ = 1/2 and σ < 1/2. We show phase diagrams of adatom arrangements, where the axes of the diagrams are the coverage σ, strength of substrate potential λ and temperature T. First, we study the case in which the natural distance between adatoms is rather short, b_nat< √2a, where a is the unit length of the substrate lattice. Then we found atoms having a "ladder structure", which fills a surface completely at σ = 3/5, as experimental results showed. At σ = 1/2, a c(2 × 2) structure is observed; the structural factor of this arrangement shows four (± 1/2, ± 1/2) spots in diffraction space. At σ < 1/2, we observed a complex structure including several ladder structures. The structural factor of this arrangement reproduces arced streaks connecting the four spots, as have been already observed more clearly by LEED. Second, in the case in which the natural distance between adatoms is larger, b_nat ≥ √2a, the ladder structure does not appear at either σ > 1/2 or σ < 1/2. Streaks appear; however, they are not arced but straight lines forming a square shape. [DOI: 10.1380/ejssnt.2005.492]

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Submonolayers of Au on Si(111) exhibit various surface superstructures, 5×2, α-√3×√3, 2√21×2√21, 6×6, and β-√3×√3, depending on the Au coverage and heat treatments. We have succeeded in detecting the clear difference in temperature dependence of electrical conductivity among these Au/Si(111) surface superstructures by using the micro-four-point probe method. The conductivity of 6×6 is higher than that of the β-√3×√3 in the whole temperature range (130-300 K), though both surfaces have the same Au coverage, but are different in long-range order of atomic arrangement. The surface conductivity of both surfaces exhibit semiconducting temperature dependence of conductivity, while that of the α-√3×√3 show a metallic character, which is consistent with surface-state bands revealed by previous photoemission spectroscopy. [DOI: 10.1380/ejssnt.2005.497]

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Surface segregation of In atoms in InGaN thin films on GaN(0001) substrate is investigated by using Monte Carlo simulations based on an empirical potential, which incorporates electrostatic energy due to bond charge and ionic charges. The calculated In composition of the surface monolayer (ML) x_s in In_0.1Ga_0.9N thin films ranging from 1 to 31 ML predicts that In atoms segregate at the topmost layer even in the film thickness t being larger than 3 ML. The x_s at the topmost layer saturates when t reaches ∼15 ML, in which x_s is much larger (x_s∼0.7) than the normal alloy composition (x ∼ 0.1). Furthermore, analysis of x_s with respect to the bulk composition x up to 0.2 reveals that the propensity of In atoms for being segregated at the surface corresponds to the bond energy difference between InN and GaN. These calculated results imply that not only the release of elastic strains due to lattice mismatch between InN and GaN but also the preference of Ga-N bonds over In-N bonds in the bulk region contributes the segregation of In atoms at the surface in InGaN thin films. [DOI: 10.1380/ejssnt.2005.503]

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The structural stability of zinc blende (ZB) structured GaN thin films on ZB-GaN(001) and ZB-SiC(001) substrates is systematically investigated based on an empirical potential, which incorporates electrostatic energy due to covalent bond charges and ionic charges. The calculated energy difference between pure ZB-GaN and mixed structure of wurtzite (W) and ZB-GaN (ZB-W-GaN) on ZB-GaN(001) implies that ZB-GaN is stabilized up to the film thickness of 554 ML. Furthermore, similar calculations incorporating misfit dislocations (MDs) on ZB-SiC(001) show that ZB-GaN pseudomorphically grown on ZB-SiC(001) initially changes its structure to ZB-GaN with MD at 28 ML in good accordance with critical thickness of misfit dislocation generation of 32 ML estimated by People-Bean formula. The ZB-GaN with MD is successively transformed into ZB-GaN with MDs at 294 ML and finally ZB-W-GaN at 865 ML. These results suggest that MD generation crucially affects the stability of ZB-GaN. [DOI: 10.1380/ejssnt.2005.507]

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We propose a novel single stranded DNA (ssDNA) immobilization process for improving sensitivity and reproducibility of DNA microarrays. We immobilized 50 mer 5'-amino-modified oligonucleotides by forming a covalent bond between the oligonucleotides, and phenylisothiocyanate groups tethered on the surface. We used a solution containing a phase-transfer catalyst, cetyltrimethylammonium bromide (CTAB). The amount of the immobilized oligonucleotides was estimated from fluorescence intensity of Cy5 dyes, which were attached to the oligonucleotides. The surface density of the immobilized oligonucleotides was also measured using X-ray reflectometry and surface plasmon resonance. We found that the addition of CTAB allowed us to increase the density and uniformity of the immobilized oligonucleotides, as well as to decrease non-specific adsorption of the oligonucleotides. The highest density and uniformity were obtained when the concentration of CTAB was nearly below the critical micelle concentration (CMC). At the concentration level close to the CMC, a CTAB monolayer formed on the surface can attract the negatively charged oligonucleotides effectively because of the positive charge of CTAB. Moreover, the CTAB layer can enhance encounter rates between the hydrophilic oligonucleotides and the hydrophobic surface with the phenylisothiocyanate groups. However, at a higher concentration level above the CMC, the density of the immobilized oligonucleotides decreases because the CTAB micelles can trap the oligonucleotides in the solution. Finally, we obtained higher hybridization signals on oligonucleotides immobilized with the CTAB solution. [DOI: 10.1380/ejssnt.2005.511]

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We theoretically study the Nernst effect and the Seebeck effect in a two-dimensional electron gas in a strong magnetic field and a temperature gradient under adiabatic condition. We recently predicted for a pure system in the quantum Hall regime that the Nernst coefficient is strongly suppressed and the thermal conductance is quantized due to quantum ballistic transport. Taking account of impurities, we here compute the Nernst coefficient and the Seebeck coefficient when the chemical potential coincides with a Landau level. We adopt the self-consistent Born approximation and consider the linear transport equations of the thermal electric transport induced by the temperature gradient. The thermal conductance and the Nernst coefficient are slightly modified from the pure case and the Seebeck coefficient newly appears because of the impurity scattering of electrons in the bulk states. [DOI: 10.1380/ejssnt.2005.518]

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Novel process for forming a gold crystal film with high (111) orientation on a substrate has been established using a supersaturated solution of [AuI₄]¯. The gold crystal film has a grain size of approximately 200 μm and an atomically flat surface, which provides sufficient quality for the substrate of SPM observation. High resolution and accuracy AFM images for a plasmid DNA thus have been obtained using the gold crystal film. [DOI: 10.1380/ejssnt.2005.524]

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