Check out our New Publishers' Select for Free Articles

Applied Surface Science (v.256, #4)

Editorial Board (pp. ii).

Preface by Tatsuo Okano Chair of the Organizing Committee (pp. 929-929).

Influence of oxygen on the growth of carbon nanotubes by the SiC surface decomposition method by T. Yamauchi; K. Nagamatsu; Y. Karayama; M. Naitoh; S. Nishigaki; H. Okado (pp. 930-933).

The influence of oxygen on the development of carbon nanotubes (CNTs) during the annealing process of the surface decomposition method on SiC(000−1) surfaces was investigated. In the case of annealing a SiC substrate under ultra-high vacuum conditions, carbon nanofibers (CNFs) form between the CNT layer and the substrate. However, CNTs form without CNFs by annealing the substrate in an oxygen atmosphere. The mean length of CNTs is longer than those formed without an oxygen atmosphere. From cross-sectional transmission electron microscopy images, it was found that oxygen plays an important role in CNT growth by the surface composition method.

Keywords: PACS; 61.46.−w; 68.37.Lp; 68.47.FgCarbon nanotubes; Surface decomposition method; TEM; Oxygen exposure

Electron affinity study of adamantane on Si(111) by W. Meevasana; R. Supruangnet; H. Nakajima; O. Topon; V. Amornkitbamrung; P. Songsiriritthigul (pp. 934-936).

Recently, tetramantane, a member of diamondoid series (C4 n₊₆H4 n₊₁₂), has shown to exhibit negative-electron-affinity effect which has a potential use for efficient electron emitting devices. Here, we explore the electronic property of adamantane (C₁₀H₁₆), the smallest member of the series. We prepare adamantane films on Si(111) substrates and then study their electronic structure with photoemission spectroscopy. Photoelectron spectra of adamantane on Si(111) have shown a peak at low-kinetic energy which could be a generic property of diamondoids. The possibility of the negative-electron-affinity effect in adamantane is further discussed.

Keywords: PACS; 73.22.−f, 79.60.−iDiamondoid; Adamantane; Electron affinity; Photoemission spectroscopy

Photocatalytic property of TiO₂ thin films sputtered-deposited on unheated substrates by Y. Pihosh; M. Goto; A. Kasahara; M. Tosa (pp. 937-942).

TiO₂ films deposited on unheated substrates of alumina silicate glass by rf. (13.56MHz) magnetron sputtering in the mixture of O₂ and Ar gases have been studied with X-ray diffraction (XRD), Atomic Force Microscopy (AFM) and optical spectroscopy. Structural and optical properties of TiO₂ films deposited at different O₂ concentrations and total pressures have been analyzed. Photocatalytic properties of TiO₂ films were characterized by following the degradation of methylene blue molecules under UV irradiation. It was found that the rate of methylene blue decomposition strongly depends on morphology and crystallinity of the deposited films, namely on the content of the anatase phase and on the size of the anatase grains. The best photocatalytic activity was found on TiO₂ films consisting of pure anatase phase with the size of grains of about 450Å. With the help of those films a thin film reactor for water purification has been designed and tested.

Keywords: PACS; 81.15Cd; 61.10.Nz; 68.37.Ps; 78.20.−eTitanium oxide; Anatase; Rutile; AFM; Photocatalysis

Infrared reflection absorption spectral study for CO adsorption on Pd/Pt(111) bimetallic surfaces by N. Todoroki; H. Osano; T. Maeyama; H. Yoshida; T. Wadayama (pp. 943-947).

Infrared reflection absorption spectroscopy (IRRAS) was used to investigate carbon monoxide (CO) adsorption on 0.15nm-thick–0.6nm-thick Pd-deposited Pt(111) bimetallic surfaces: Pd_x/Pt(111) (where x is the Pd thickness in nanometers) fabricated using molecular beam epitaxial method at substrate temperatures of 343K, 473K, and 673K. Reflection high-energy electron diffraction (RHEED) measurements for Pd0.15–0.6_nm/Pt(111) surfaces fabricated at 343K showed that Pd grows epitaxially on a clean Pt(111), having an almost identical lattice constant of Pt(111). The 1.0L CO exposure to the clean Pt(111) at room temperature yielded linearly bonded and bridge-bonded CO–Pt bands at 2093 and 1855cm⁻¹. The CO–Pt band intensities for the CO-exposed Pd_x/Pt(111) surfaces decreased with increasing Pd thickness. For Pd0.3_nm/Pt(111) deposited at 343K, the 1933cm⁻¹ band caused by bridge-bonded CO–Pd enhanced the spectral intensity. The linear-bonded CO–Pt band (2090cm⁻¹) almost disappeared and the bridge-bonded CO–Pd band dominated the spectra for Pd0.6_nm/Pt(111). With increasing substrate temperature during the Pd depositions, the relative band intensities of the CO–Pt/CO–Pd increased. For the Pd0.3_nm/Pt(111) deposited at 673K, the linear-bonded CO–Pt and bridge-bonded CO–Pd bands are located respectively at 2071 and 1928cm⁻¹. The temperature-programmed desorption (TPD) spectrum for the 673K-deposited Pd0.3_nm/Pt(111) showed that a desorption signal for the adsorbed CO on the Pt sites decreased in intensity and shifted ca. 20K to a lower temperature than those for the clean Pt(111). We discuss the CO adsorption behavior on well-defined Pd-deposited Pt(111) bimetallic surfaces.

Keywords: Pt(1; 1; 1); Palladium; Infrared reflection absorption spectroscopy; Thermal desorption spectroscopy; Carbon monoxide; Reflection high-energy electron diffraction

Study of electronic states for V thin films deposited on 6H-SiC substrates by soft X-ray emission spectroscopy by M. Hirai; H. Okazaki; R. Yoshida; M. Tajima; K. Saeki; Y. Muraoka; T. Yokoya (pp. 948-949).

Silicon carbide (SiC) is a candidate material for electronic devices to operate upon crucial environment. Electronic states of silicides and/or carbide/graphite formed in metal/SiC contact system is fundamentally important from the view point of device performance.We study interface electronic structure of vanadium (V) thin-film deposited on 6H-SiC(0001) Si-face by using a soft X-ray emission spectroscopy (SXES). For specimens of V(38nm)/6H-SiC (substrate) contact systems annealed at 850°C, the Si L_2,3 emission spectra indicate different shapes and peak energies from the substrate. The product of materials such as silicides and/or ternary materials is suggested. Similarly, the C Kα emission spectra show the shape and peak energy characteristic of vanadium carbide including substrate 6H-SiC signal.

Keywords: PACS; 68.35.−p; 73.20.−rSXES; 6H-SiC; Silicide; Vanadium

Estimation of surface charges on dielectric materials for high power rf windows by Shinichiro Michizono; Yoshio Saito; Suharyanto; Yasushi Yamano; Shinichi Kobayashi (pp. 950-953).

The surface discharges observed at rf windows and vacuum circuit breakers (VCBs) are one of the difficulties faced when developing high-power rf windows or compact VCBs. The surface discharge is considered to take place due to the release of the surface charges. Despite the importance of the surface charging/discharging, these phenomena have not been well evaluated. In this paper, the surface charges are estimated using the multipulse method, where electron beam irradiates a sample up to the saturation condition of surface charges. The amount of surface charges on alumina and TiN coated alumina are compared and the charging mechanism is discussed.

Keywords: PACS; 79.20.HxSecondary electron; Charging; Insulator; Alumina

Luminescence properties of Ge implanted SiO₂:Ge and GeO₂:Ge films by Nobutoshi Arai; Hiroshi Tsuji; Masashi Hattori; Masayuki Ohsaki; Hiroshi Kotaki; Toyotsugu Ishibashi; Yasuhito Gotoh; Junzo Ishikawa (pp. 954-957).

We have investigated cathodeluminescence (CL) of Ge implanted SiO₂:Ge and GeO₂:Ge films. The GeO₂ films were grown by oxidation of Ge substrate at 550°C for 3h in O₂ gas flow. The GeO₂ films on Ge substrate and SiO₂ films on Si substrate were implanted with Ge-negative ions. The implanted Ge atom concentrations in the films were ranging from 0.1 to 6.0at%. To produce Ge nanoparticles the SiO₂:Ge films were thermally annealed at various temperatures of 600–900°C for 1h in N₂ gas flow. An XPS analysis has shown that the implanted Ge atoms were partly oxidized. CL was observed at wavelengths around 400nm from the GeO₂ films before and after Ge⁻-implantation as well as from SiO₂:Ge films. After Ge⁻-implantation of about 0.5at% the CL intensity has increased by about four times. However, the CL intensity from the GeO₂:Ge films was several orders of magnitude smaller than the intensity from the 800°C-annealed SiO₂:Ge films with 0.5at% of Ge atomic concentration. These results suggested that the luminescence was generated due to oxidation of Ge nanoparticles in the SiO₂:Ge films.

Keywords: PACS; 61.72.Tt; 41.75.Cn; 61.72.Ww; 81.07.−b; 81.40.Gh; 78.60.HfIon implantation; Heat treatment; Germanium; Cathodeluminescence

Estimation of secondary electron effect in the J-PARC rapid cycling synchrotron after first study by Kazami Yamamoto; Junichiro Kamiya; Norio Ogiwara; Michikazu Kinsho; Naoki Hayashi; Ryuji Saeki; Kenichirou Satou; Takeshi Toyama (pp. 958-961).

The J-PARC 3GeV rapid-cycling synchrotron (RCS) is required to provide 1MW pulsed protons to the spallation neutron target and the 50GeV main ring. Since the RCS finally accelerates very high intensity beam such as 8.3×10¹³ppp, the secondary electron cloud may affect the accelerator performance. We measured the secondary electron emission from the TiN coating surface and the ferrite sample. By using these measurement results, we estimated the effect of the electron cloud made by the emitted secondary electron at present beam parameters.

Keywords: PACS; 07.30TJ-PARC; RCS; Proton accelerator; Secondary electron emission; TiN; Ferrite

Observation of internal-conversion electrons induced by inelastic nuclear resonant scattering by Taizo Kawauchi; Katsuyuki Fukutani; Tatsuo Okano; Shunji Kishimoto; Xiaowei Zhang; Yoshitaka Yoda (pp. 962-964).

Measurements of the internal-conversion electron emission due to the inelastic nuclear resonant excitation are reported.Fe57 thin films of 20 and 1.3nm thickness were deposited on Si(111), and the internal-conversion electrons were measured as a function of the photon energy. From the inelastic part of the spectra, the phonon density of states was obtained. Whereas the phonon density of states of 20-nm thick film resembles that of bulkα-Fe, the 1.3-nm thick film revealed an obvious softening of the acoustic mode.

Keywords: PACS; 63.22.; −; m; 76.80.+yConversion electron; Nuclear inelastic resonance

Exit angle dependence of charge-state distribution of backscattered He ions by Kaoru Sasakawa; Kaoru Nakajima; Motofumi Suzuki; Kenji Kimura (pp. 965-967).

Exit angle and energy dependences of the charge-state distribution of backscattered He ions were investigated when 500keV He⁺ ions were incident on SiO₂. The energy dependence of the He⁺ fraction was estimated by comparing the measured He⁺ spectra with the simulated spectra of He ions in all charge states at the exit angles of 5–25° with respect to the SiO₂ surface. We found that the He⁺ fraction is almost independent of the exit angle at energies higher than 250keV and the observed energy dependence of the He⁺ fraction is in good agreement with that for the carbon-foil-transmission experiment. In the low energy region (<250keV), however, the He⁺ fraction decreases as the exit angle decreases.

Keywords: PACS; 25.55.Kr; 82.80.YcCharge-state distribution; High-resolution Rutherford backscattering spectrometry; Charge exchange; Practical surface

Comparative study of ethanol sensor based on gold nanoparticles: ZnO nanostructure and gold: ZnO nanostructure by E. Wongrat; P. Pimpang; S. Choopun (pp. 968-971).

Gold colloid:ZnO nanostructures were prepared from Zn powder by using thermal oxidation technique on alumina substrates, then it was impregnated by gold colloid for comparative study. The gold colloid is the solution prepared by chemical reduction technique; it appeared red color for gold nanoparticle solution and yellow color for gold solution. The heating temperature and sintering time of thermal oxidation were 700°C and 24h, respectively under oxygen atmosphere. The structural characteristics of gold colloid:ZnO nanostructures and pure ZnO nanostructures were studied using filed emission scanning electron microscope (FE-SEM). From FE-SEM images, the diameter and length of gold colloid:ZnO nanostructures and ZnO nanostructures were in the ranges of 100–500nm and 2.0–7.0μm, respectively. The ethanol sensing characteristics of gold colloid:ZnO nanostructures and ZnO nanostructures were observed from the resistance alteration under ethanol vapor atmosphere at concentrations of 50, 100, 200, 500, and 1000ppm with the operating temperature of 260–360°C. It was found that the sensitivity of sensor depends on the operating temperature and ethanol vapor concentrations. The sensitivity of gold colloid:ZnO nanostructures were improved with comparative pure ZnO nanostructures, while the optimum operating temperature was 300°C. The mechanism analysis of sensor revealed that the oxygen species on the surface was O²⁻.

Keywords: PACS; 81.05.Dz; 81.65.Mq; 61.46.Df; 82.70.DdEthanol sensor; ZnO nanostructures; Gold nanoparticles; Gold colloid

Ion-induced self-organized ripple patterns on graphite and diamond surfaces by K. Takahiro; K. Ozaki; K. Kawatsura; S. Nagata; S. Yamamoto; K. Narumi; H. Naramoto (pp. 972-975).

In order to investigate the allotropic effect on ripple pattern formation, highly oriented pyrolytic graphite (HOPG) and single crystalline diamond were irradiated with 10–200keV Xe⁺ at an incident angle of 60° with respective to the surface normal. The irradiation fluence was 2×10¹⁷cm⁻² for all irradiations. Ripple patterns were observed on both HOPG and diamond surfaces. However, large differences in ripple wavelengths, amplitudes and surface roughnesses between HOPG and diamond were recognized. The reason for these differences is discussed.

Keywords: PACS; 79.60.Jv; 81.07.Bc; 73.22.-fSputter erosion; Ripple; Graphite; Diamond; Atomic force microscope; Ion beam

Influence of nanometer scale film structure of ZDDP tribofilm on Its mechanical properties: A computational chemistry study by Tasuku Onodera; Takanori Kuriaki; Yusuke Morita; Ai Suzuki; Michihisa Koyama; Hideyuki Tsuboi; Nozomu Hatakeyama; Akira Endou; Hiromitsu Takaba; Carlos A. Del Carpio; Momoji Kubo; Clotilde Minfray; Jean-Michel Martin; Akira Miyamoto (pp. 976-979).

We investigated the influence of a nanometer scale film structure of a tribofilm generated from zinc dialkyldithiophosphate (ZDDP) anti-wear additive on its mechanical properties using a combined molecular dynamics (MD) and finite element (FE) method. The frictional behavior of an interface between a native iron oxide layer on steel surface and zinc metaphosphate – regarded as a model material of ZDDP tribofilm – was firstly studied using the MD method. The results showed that the iron atoms in the oxide layer diffused into the phosphate layer during the friction process. The zinc atoms in the phosphate layer also diffused into the oxide layer. Significant interdiffusion of iron and zinc atoms was observed with increasing simulation time. Thus, metallic phosphate with a gradient composition of iron and zinc atoms was formed on the phosphate/oxide interface. We then constructed an axisymmetric nanoindentation simulation model from the MD-derived structures at a certain simulation time and carried out a FE calculation. As a result, we found that the rubbed ZDDP tribofilm, including the phosphate with the gradient composition of metallic atoms, showed larger contact stiffness and hardness. The combined MD/FE simulation indicates that the tribofilm becomes stiffer and harder due to the interdiffusion of iron and zinc atoms on the tribofilm/oxide interface. We have found that the gradient composition formation in ZDDP tribofilm during friction process influences on its mechanical properties.

Keywords: PACS; 81.40.Pq; 82.45.Mp; 46.55.+d; 31.15.xvComputational chemistry; ZDDP; Gradient composition; Mechanical properties

In situ monitoring of ZnO formation by photoemission spectroscopy by Suttinart Noothongkaew; Ratchadaporn Supruangnet; Worawat Meevasana; Hideki Nakajima; Sukit Limpijumnong; Prayoon Songsiriritthigul (pp. 980-983).

Exposure of a clean Zn metal to oxygen in ultra high vacuum provides a mean to gradually form ZnO. With in situ synchrotron photoelectron measurement, the progressive change in the spectra with the oxygen exposure time is observed. The analysis of the spectra allows the determination of ZnO formation. It was found that the oxidation process takes place until reaching the critical thickness, at which the oxidation rate reduces greatly to nearly zero. The critical thickness was determined to be about 2 monolayers.

Keywords: PACS; 82.40.−g; 82.65.+r; 68.47.Gh; 79.60−iZnO; Oxidation of Zn; Photoemission spectroscopy; Synchrotron radiation

Measurement of diffusion process of iron atoms under high pressure of hydrogen by time-domain analysis of nuclear resonant scattering of X-rays by Hidetaka Kasai; Taizo Kawauchi; Yuh Fukai; Xiao-Wei Zhang; Shunji Kishimoto; Takumi Kikegawa; Eiji Ohtani; Tatsuo Okano (pp. 984-986).

We applied the time-domain analysis of nuclear resonant scattering (NRS) of X-rays for the study of the hydrogen-induced enhancement of atomic diffusion. The time-domain analysis of NRS is a powerful technique for studying diffusion processes on an atomic scale. The NRS measurement combined with high-pressure technique enables the direct measurement of self-diffusion processes under high hydrogen pressures. In this preliminary experiment, self-diffusion in 4μm thick⁵⁷Fe foils at 0.8GPa was investigated. The samples of the⁵⁷Fe were encapsulated with MgO or NaCl. Faster decays caused by diffusion of Fe atoms were observed in the time spectra of NRS at high temperatures. This enhancement of diffusion is believed to be the hydrogen-induced effect. In the present experiment, hydrogen should have been supplied to the samples by reaction with water originally adsorbed on NaCl/MgO powder particles. It was concluded that the diffusion of⁵⁷Fe atoms under high pressure can be studied by nuclear resonant scattering of X-rays using a compact cubic-anvil press. The NRS method can also be extended to the study of atomic diffusion in the subsurface region by doping⁵⁷Fe layer(s) at known depths.

Keywords: Diffusion; Iron; Hydrogen; Nuclear resonant scattering; High pressure

Analysis of the number of hydrogen bond groups of a multiwalled carbon nanotube probe tip for chemical force microscopy by Hiroaki Azehara; Hiroshi Tokumoto (pp. 987-990).

In this paper, we describe a statistical method of quantification of the number of functional groups at the contact area of a probe tip for atomic force microscopy from the result of repetitive pull-off force measurements. We have investigated laboratory-made carbon nanotube (CNT) probe tips to apply them for chemical force microscopy because limited number of functional groups at the tip-end is expected. Using a CNT tip, we conducted repetitive pull-off force measurements against a self-assembled monolayer terminated with carboxyl group and analyzed them in terms of the number of hydrogen bond groups at the CNT tip. The elementary hydrogen bond rupture force quantum in n-decane medium was estimated to be 84.2±0.5pN in the present system. Thus it was revealed that only a couple of hydrogen bond groups of the CNT tip were participating in hydrogen bonding with the sample on an average in this experimental system.

Keywords: PACS; 68.37.PsForce spectroscopy; Chemical force microscopy; Carbon nanotube probe tips; Intermolecular interactions; Bond rupture forces

Sputtering of neutral clusters from silver–gold alloys by B.V. King; J.F. Moore; I.V. Veryovkin; A.V. Zinovev; M.J. Pellin (pp. 991-994).

Polycrystalline Ag, Ag₂₀Au₈₀, Ag₄₀Au₆₀, Ag₈₀Au₂₀ and Au samples were bombarded with 15keV Ar⁺ at 60° incidence and the resulting secondary neutral yield distribution was studied by non-resonant laser postionisation mass spectrometry. Neutral clusters containing up to 21 atoms were observed for the targets. The yield of neutral clusters, Ag_mAu n−_m, containing n atoms, Y_n, was found to follow a power in n, i.e. Y_n∝ n−^δ, where the exponent δ varied from 3.2 to 4.0. For a fixed n, the cluster yields showed a variation with number of gold atoms similar to that expected for a binomial distribution. In addition, the cluster compositions from the sputtered alloys were indicative of sputtering from a gold rich surface.

Keywords: PACS; 61.80.Jh; 61.82.Bg; 68.49.SfSputtering; Clusters; SNMS; Photoionisation

An orientation analysis method for protein immobilized on quantum dot particles by Satoka Aoyagi; Masae Inoue (pp. 995-997).

The evaluation of orientation of biomolecules immobilized on nanodevices is crucial for the development of high performance devices. Such analysis requires ultra high sensitivity so as to be able to detect less than one molecular layer on a device. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) has sufficient sensitivity to evaluate the uppermost surface structure of a single molecular layer. The objective of this study is to develop an orientation analysis method for proteins immobilized on nanomaterials such as quantum dot particles, and to evaluate the orientation of streptavidin immobilized on quantum dot particles by means of TOF-SIMS. In order to detect fragment ions specific to the protein surface, a monoatomic primary ion source (Ga⁺) and a cluster ion source (Au₃⁺) were employed. Streptavidin-immobilized quantum dot particles were immobilized on aminosilanized ITO glass plates at amino groups by covalent bonding. The reference samples streptavidin directly immobilized on ITO plates were also prepared. All samples were dried with a freeze dryer before TOF-SIMS measurement. The positive secondary ion spectra of each sample were obtained using TOF-SIMS with Ga⁺ and Au₃⁺, respectively, and then they were compared so as to characterize each sample and detect the surface structure of the streptavidin immobilized with the biotin-immobilized quantum dots. The chemical structures of the upper surface of the streptavidin molecules immobilized on the quantum dot particles were evaluated with TOF-SIMS spectra analysis. The indicated surface side of the streptavidin molecules immobilized on the quantum dots includes the biotin binding site.

Keywords: TOF-SIMS; Protein orientation; Quantum dot; Cluster ion source

Zinc oxide nanostructures for applications as ethanol sensors and dye-sensitized solar cells by Supab Choopun; Auttasit Tubtimtae; Theerapong Santhaveesuk; Sanpet Nilphai; Ekasiddh Wongrat; Niyom Hongsith (pp. 998-1002).

ZnO nanostructures were prepared by thermal oxidation technique for applying as ethanol sensors and dye-sensitized solar cells. To improve sensitivity of the sensor based on ZnO nanostructures, gold doping was performed in ZnO nanostructures. Gold-doped with 0%, 5%, and 10% by weight were investigated. The improvement of sensor sensitivity toward ethanol due to gold doping was observed at entire operating temperature and ethanol concentration. The sensitivity up to 145 was obtained for 10% Au-doped ZnO sensor. This can be explained by an increase of the quantity of oxygen ion due to catalytic effect of gold. Also, it was found that oxygen ion species at the surface of the Au-doped ZnO sensor remained O²⁻ as pure ZnO sensor. For dye-sensitized solar cell application, the dye-sensitized solar cell structure based on ZnO as a photoelectrode was FTO/ZnO/Eosin-Y/electrolyte/Pt counter electrode. ZnO with different morphologies of nanobelt, nano-tetrapod, and powder were investigated. It was found that DSSCs with ZnO powder showed higher photocurrent, photovoltage and overall energy conversion efficiencies than that of ZnO nanobelt and ZnO nano-tetrapod. The best results of DSSCs were the short circuit current ( J_sc) of 1.25mA/cm², the open circuit voltage ( V_oc) of 0.45V, the fill factor (FF) of 0.65 and the overall energy conversion efficiency ( η) of 0.68%.

Keywords: PACS; 81.05.Dz; 81.10.Bk; 81.65.Mq; 73.61.GA; 82.47.JkZinc oxide; ZnO; Nanostructure; Sensor; Dye-sensitized solar cell; Solar cell

Field emission measured from nanostructured germanium and silicon thin films by D.A. Carder; A. Markwitz (pp. 1003-1005).

We have prepared nanostructured thin films of germanium and silicon. The films were grown by an ion beam sputtering technique followed by a rapid annealing step using an electron beam annealer. The annealing temperature is a comparatively low 500°C, resulting in well defined nano-islands on the film surface. Electron field emission has been measured from the surfaces under high vacuum. The threshold electric field value for significant current flow was measured as 2.5Vμm⁻¹ for a silicon thin film which is comparable to other silicon technologies. A value of 0.5Vμm⁻¹ for a germanium thin film represents an order of magnitude improvement for related germanium nanostructured systems.

Keywords: PACS; 85.45.Db; 81.05.Cy; 81.16.Dn; 81.15.Cd; 81.15.JjField emission; Nanostructures; Ion beam sputtering; Electron beam annealing; Silicon; Germanium

Field emission properties of nano-structured phosphorus-doped diamond by Takatoshi Yamada; Christoph E. Nebel; Shin-ichi Shikata (pp. 1006-1009).

Nano-structured phosphorus-doped diamonds were fabricated for field emitters and their field emission properties were characterized. Two kinds of nano-structures were prepared; tip array structures and whiskers on tip structures. The tips, which have 100nm radius and 10μm height, are used in tip array structures; whiskers have tip radii of 5nm and height of 500nm. Following nano-structure formation, a reduction of threshold fields is observed compared to non-patterned flat surfaces. This is ascribed to field concentration at the tips. However, at higher electric fields, a saturation of the emission current is observed due to non-negligible bulk resistances in tips and whiskers.

Keywords: Diamond; Field emission; Nano-fabrication; Electron affinity; Field enhancement

A study on the optical and electrical properties of direct-patternable ZnO films incorporated various contents of Pt nanoparticles by Yong-June Choi; Seok-Joo Wang; Hyuncheol Kim; Kyoung-Hoe Koo; Hyung-Ho Park (pp. 1010-1013).

Platinum nanoparticles were synthesized by the methanol reduction method, and their size was controlled to 3nm on average using PVP [poly( N-vinyl-2-pyrrolidon)] as a protecting unit. Various contents of Pt nanoparticles were incorporated into ZnO solutions which were synthesized by a sol–gel process. ZnO films with Pt nanoparticles of various content were annealed at 500°C and 600°C for 1h. The crystallinity increased with the annealing temperature and also slightly with the content of Pt nanoparticles. The sheet resistance of ZnO films decreased with the incorporation of Pt nanoparticles, however the decreasing behavior was not maintained with increasing content of Pt nanoparticles. A shift of valence band maximum energy of ZnO film with Pt nanoparticles to higher energy was also observed due to electron transfer from Pt nanoparticles to ZnO film. The optical transmittance was 88±2% in the visible region for all the ZnO films. Well-defined 60μm wide direct-patterned ZnO films containing Pt nanoparticles of 0.5 atomic percent could be formed without using dry etching process.

Keywords: PACS; 73.61.GaZnO film; Pt nanoparticles; Photochemical solution deposition; Direct patterning

Characterization of Cr/6H-SiC(0001) nano-contacts by current-sensing AFM by Miłosz Grodzicki; Szymon Smolarek; Piotr Mazur; Stefan Zuber; Antoni Ciszewski (pp. 1014-1018).

The electrical properties and interface chemistry of Cr/6H-SiC(0001) contacts have been studied by current-sensing atomic force microscopy (CS-AFM) and X-ray photoelectron spectroscopy (XPS). Cr layers were vapor deposited under ultrahigh vacuum onto both ex situ etched in H₂ and in situ Ar⁺ ion-bombarded samples. The Cr/SiC contacts are electrically non-uniform. Both the measured I– V characteristics and the modeling calculations enabled to estimate changes of the Schottky barrier height caused by Ar⁺ bombardment. Formation of ohmic nano-contacts on Ar⁺-bombarded surfaces was observed.

Keywords: PACS; 72.80.Jc; 79.60.Dp; 68.37.PsSilicon carbide; AFM; Chromium; Electric contacts

Novel materials for electronic device fabrication using ink-jet printing technology by Yasushi Kumashiro; Hideo Nakako; Maki Inada; Kazunori Yamamoto; Akira Izumi; Masamichi Ishihara (pp. 1019-1022).

Novel materials and a metallization technique for the printed electronics were studied. Insulator inks and conductive inks were investigated. For the conductive ink, the nano-sized copper particles were used as metallic sources. These particles were prepared from a copper complex by a laser irradiation process in the liquid phase. Nano-sized copper particles were consisted of a thin copper oxide layer and a metal copper core wrapped by the layer. The conductive ink showed good ink-jettability. In order to metallize the printed trace of the conductive ink on a substrate, the atomic hydrogen treatment was carried out. Atomic hydrogen was generated on a heated tungsten wire and carried on the substrate. The temperature of the substrate was up to 60°C during the treatment. After the treatment, the conductivity of a copper trace was 3μΩcm. It was considered that printed wiring boards can be easily fabricated by employing the above materials.

Keywords: Atomic hydrogen; Laser ablation; Deoxidization; Ink-jet; Printed wiring boards

Surface and electrical properties of organic–inorganic hybrid structure as gate insulator to organic thin film transistor by Yong Seob Park; Sang-Jin Cho; Jin-Hyo Boo; Byungyou Hong (pp. 1023-1027).

Carbon-based OTFT devices were fabricated using a plasma process for the gate electrode and gate insulators. A nanocrystalline carbon (nc-C) film was used as the gate electrode, and three different layers, cyclohexene, diamond-like carbon (DLC), and cyclohexene/DLC (hybrid insulator), were used as the gate insulator. The surface and electrical properties of the three different gate insulators on the nc-C gate electrode were investigated using the SPM method, and the leakage current density and dielectric constant of the metal–insulator–metal (MIM) structures with three different insulator layers were evaluated. The hybrid insulator layer had a very smooth surface, approximately 0.2nm, a uniform surface without defects, and good adhesion between the layers. Overall, it is believed that the hybrid insulator lead to a decrease in the electrical leakage current and an improvement in the device performance.

Keywords: Organic thin film transistor; Nanocrystalline carbon; Hybrid insulator; RF-PECVD

Control of nanogap junction resistance by imposed pulse voltage by Yuichiro Masuda; Tsuyoshi Takahashi; Shigeo Furuta; Masatoshi Ono; Tetsuo Shimizu; Yasuhisa Naitoh (pp. 1028-1030).

The resistance switching effect of a simple gold nanogap junction was investigated. This device exhibits highly reproducible switching and nonvolatile characteristics. The resistance switching was developed for dependence of the resistance on the applied voltage level. Four separate ranges of resistance were repeatedly controlled by programmed sequential application of voltage pulses, including the operation of data verification.

Keywords: PACS; 81.07.−b; 81.16.TaNonvolatile memory; Photolithograph; Nanogap electrodes; Shadow evaporation; Resistance switch

Observation of new critical point in In_xAl1−_xAs alloy using spectroscopic ellipsometry by J.J. Yoon; T.H. Ghong; J.S. Byun; Y.J. Kang; Y.D. Kim; H.J. Kim; Y.C. Chang; J.D. Song (pp. 1031-1034).

Using a spectroscopic ellipsometry, pseudodielectric functions 〈 ɛ〉 of In_xAl1−_xAs ternary alloy films ( x=0.43, 0.62, 0.75, and 1.00) from 0.74 to 6.48eV were determined. Fast in-situ chemical etching to effectively remove surface overlayers using charge-coupled device detector and to avoid the reoxidation of the surface of films prior to the ellipsometric spectrum measurement was performed. At the high energy region, an additional critical point structure which is interpreted as the E′₁ transition from the band structure calculation of the linear augmented Slater-type orbital method was reported.

Keywords: PACS; 78.20.Ci; 78.66.Fd; 71.20.NrEllipsometry; InAlAs; Dielectric function; Band calculation; LASTO

Design of a mirror aberration corrector and a beam separator for LEEM by K. Tsuno; T. Yasue; T. Koshikawa (pp. 1035-1041).

A SPLEEM (spin polarized low energy electron microscope) has been designed with a numerical simulation of electrostatic and magnetic field distributions and electron ray trajectories. Highly (more than 90%) spin polarized electron source has been used. A Wien type spin manipulator and a magnetic lens type spin rotator are used to align spin direction. A magnetic field free objective lens is designed to observe magnetic domain structure of magnetic materials. High or low magnification mode can be selected by using a combined electrostatic and magnetic objective lens for a high spatial resolution and a wide imaging area observation. An electrostatic mirror aberration corrector is installed after the image forming objective lens. A double deflection 45° beam separator is used to bend the direction of electrons from the source to the objective lens and from the objective lens to the mirror aberration corrector.

Keywords: PACS; 41.85.Gy, 41.85.LcLEEM, SPLEEM, Mirror corrector, Beam separator, Cathode lens

Superior capacitive characteristics of RuO₂ nanorods grown on carbon nanotubes by Yu-Sheng Lin; Kuei-Yi Lee; Kuei-Yu Chen; Ying-Sheng Huang (pp. 1042-1045).

Carbon nanotubes (CNTs) were used as the electric double layer capacitor (EDLC) material and were synthesized by using thermal chemical vapor deposition (TCVD). To enhance the EDLC capacity, the ruthenium dioxide (RuO₂) nanorods were grown on CNTs by using metal organic chemical vapor deposition (MOCVD). The synthesized CNTs were the principal part and template, and the RuO₂ nanorods were grown outwardly from CNTs. The increase of effective specific area between electrode and electrolyte played an important role in enhancing the capacitance. Different concentrations of KOH were used as electrolyte to measure the capacitance to find the variation of capacitance. Moreover, the RuO₂/CNT composites demonstrated a stable cycle life. The results showed that the RuO₂/CNT composites were a promising supercapacitor device material.

Keywords: Carbon nanotubes; Ruthenium dioxide; Electric double layer capacitor; Electrolyte concentration

Electronic excitation processes in rare gas clusters studied by electron energy loss spectroscopy by Hayato Kubotera; Satoshi Sakai; Tatsuya Sekitsuka; Takayuki Tachibana; Takato Hirayama (pp. 1046-1049).

We present the electron energy loss spectra for Ar clusters as a function of incident electron energy and of cluster size. In spectra measured with 100eV incident electron energy the bulk excitation peak becomes visible for a mean cluster size above 170 atoms per cluster. For 250eV incident electron energy the bulk excitation peak is clearly observable even for a mean cluster size of 120 atoms per cluster. These experimental results are qualitatively reproduced by a simple calculation that accounts for the mean free path of electrons in Ar clusters; i.e., the penetration depth of incident electrons into the cluster.

Keywords: Rare gas; Cluster; Energy loss spectroscopy

Preparation of WO₃ nanoparticles and application to NO₂ sensor by Dan Meng; Toshinari Yamazaki; Yanbai Shen; Zhifu Liu; Toshio Kikuta (pp. 1050-1053).

WO₃ nanoparticles were prepared by evaporating tungsten filament under a low pressure of oxygen gas, namely, by a gas evaporation method. The crystal structure, morphology, and NO₂ gas sensing properties of WO₃ nanoparticles deposited under various oxygen pressures and annealed at different temperatures were investigated. The particles obtained were identified as monoclinic WO₃. The particle size increased with increasing oxygen pressure and with increasing annealing temperature. The sensitivity increased with decreasing particle size, irrespective of the oxygen pressure during deposition and annealing temperature. The highest sensitivity of 4700 to NO₂ at 1ppm observed in this study was measured at a relatively low operating temperature of 50°C; this sensitivity was observed for a sensor made of particles as small as 36nm.

Keywords: WO; ₃; Gas evaporation; Nanoparticle; Gas sensor; NO; ₂

Theoretical investigation on the structural stability of GaP nanowires with{111} facets by Tomoki Yamashita; Toru Akiyama; Kohji Nakamura; Tomonori Ito (pp. 1054-1057).

The structural stability of GaP nanowires (NWs) with{111} facets including twin planes is systematically investigated using our empirical potentials which incorporate the electrostatic interaction between surface cations and anions. The cohesive energy of GaP NWs for diameter of∼30nm demonstrates that the wurtzite structure is the most stable over entire diameter range. This is because the electrostatic interaction between surface cations and anions is dominant around twin planes, resulting in the small energy deficit compared to that on polar{111} facets. By comparing the cohesive energy of GaP NWs consisting of{111}/{11¯00} facets with that of{11¯0}/{112¯0} facets, the NWs consisting of{11¯0}/{112¯0} facets are found to be favorable than those consisting of{111}/{11¯00} facets over entire diameter range. These results imply that growth processes such as vapor–liquid–solid mechanism could affect on the formation of NWs consisting of{111}/{11¯00} facets.

Keywords: PACS; 81.07.Bc; 81.10.; −; h; 61.46.+wNanowires; GaP; Structural stability; {; 1; 1; 1; }; Facets; {; 1; 1; ¯; 0; }; Facets

Verwey transition in spin polarization of field-emitted electrons from 〈110〉-oriented single crystal magnetite whisker by Shigekazu Nagai; Koichi Hata; Morihiro Okada; Hidenori Mimura (pp. 1058-1060).

We measured temperature dependence of a spin polarization of field-emitted electrons from a single-crystalline magnetite (Fe₃O₄) whisker with 〈110〉 orientation. The spin polarization of emitted electrons began to increase above 130K corresponding to the temperature of Verwey point ( T_v). The increase is considered as reflection of the change of the spin state near the Fermi level due to the Verwey transition. Our experimental results support a localization of t_2g orbital electrons below the Verwey point and a model of charge ordering for magnetite.

Keywords: Spintronics; Field emission; Magnetite; Fe; ₃; O; ₄; Verwey transition; Spin polarization

Application of X-ray photoelectron spectroscopy to characterization of Au nanoparticles formed by ion implantation into SiO₂ by K. Takahiro; S. Oizumi; K. Morimoto; K. Kawatsura; T. Isshiki; K. Nishio; S. Nagata; S. Yamamoto; K. Narumi; H. Naramoto (pp. 1061-1064).

In X-ray photoelectron spectroscopy (XPS) of Au nanoparticles, the width of 5 d valence band changes with Au particle size. This enables us to estimate the size of Au nanoparticles by using XPS. In this work, the 5 d-band width has been measured for Au nanoparticles formed by ion implantation into SiO₂. The 5 d-band width is found to be correlated strongly with the Au concentration. As the Au concentration increases, the 5 d-band width becomes larger, indicating that the Au nanoparticles with the larger size tend to be formed in the vicinity of the projected range of Au ions. This correlation agrees very well with the results from transmission electron microscopy.

Keywords: PACS; 79.60.Jv; 81.07.Bc; 73.22.−fNanoparticle; X-ray photoelectron spectroscopy; Au; SiO; ₂; Valence band; Ion implantation

Growth of carbon nanotubes on stainless steel substrates by DC-PECVD by Dao Quang Duy; Hyun Suk Kim; Dang Mo Yoon; Kang Jae Lee; Jung Woong Ha; Yong Gyoo Hwang; Choong Hun Lee; Bach Thanh Cong (pp. 1065-1068).

We report on the fabrication of carbon nanotubes (CNTs) on Ni-coated stainless steel (SUS) substrates by using dc plasma enhanced chemical vapor deposition. The synthesized CNTs have the diameter of about 30nm and the length of about 1.2μm. To verify the effects of SUS substrates on the growth of CNTs, CNTs had also been grown on Ni-coated Si substrates. CNTs grown on the SUS substrates were more uniform compared with those grown on the Si substrates. Field emission properties of the CNT films were measured in the diode configuration, and the turn-on electric field of 3.87V/μm and field enhancement factor β of about 1737 were obtained from the synthesized CNTs at the gap of 500μm between the SUS substrate and the anode. These results have not only clarified the effects of the substrate on the growth of CNTs, but also shown the potential of CNTs in field emission applications, especially CNT-based cold-cathode X-ray tubes.

Keywords: PACS; 72.80Carbon nanotube; DC-PECVD; Pretreatment; SUS; Field emission

Growth and characterization of Fe nanostructures on GaN by Yuya Honda; Satoko Hayakawa; Shigehiko Hasegawa; Hajime Asahi (pp. 1069-1072).

We have investigated the growth of Fe nanostructures on GaN(0001) substrates at room temperature using reflection high-energy electron diffraction (RHEED), scanning tunneling microscopy (STM), and superconducting quantum interference device magnetometer. Initially, a ring RHEED pattern appears, indicating the growth of polycrystalline α-Fe. At around 0.5nm deposition, the surface displays a transmission pattern from α-Fe films with the epitaxial relationship of Fe(110)//GaN(0001) and Fe[1−11]//GaN[11−20] (Kurdjumov–Sachs (KS) orientational relationship). Further deposition to 1nm results in the appearance of a new spot pattern together with the pattern from domains with the KS orientation relationship. The newly observed pattern shows that Fe layers are formed with the epitaxial relationship of Fe(110)//GaN(0001) and Fe[001]//GaN[11−20] (Nishiyama–Wasserman (NW) orientational relationship). From STM images for Fe layers with the KS and NW orientational relationships, it can be seen that Fe layers with the KS relationship consist of round-shaped Fe nanodots with below 7nm in average diameter. These nanodots coalesce to form nanodots elongating along the Fe[100] direction, and they have the KS orientational relationship. Elongated Fe nanodots with the NW relationship show ferromagnetism while round-shaped Fe nanodots with the KS relationship show super-paramagnetic behavior. We will discuss their magnetic properties in connection with the change in crystalline configurations of nanodots.

Keywords: PACS; 68.37.Ef; 75.75.+aSTM; Nanostructure; Magnetic property; Fe; GaN

A study on the structural and mechanical properties of ordered mesoporous Al₂O₃ film by Tae-Jung Ha; Hyung-Ho Park; Seok-Jin Yoon; Jin-Sang Kim (pp. 1073-1077).

Ordered mesoporous aluminum oxide films with a porosity range of 40–48% were synthesized by an evaporation-induced self-assembly (EISA) process using surfactant templating. To investigate the role of the hydrolysis reaction in the formation of a mesoporous structure, the changes of pore structure properties according to a variation of aging time and water molar ratio were monitored. From the tendencies of pore structure properties, the optimized condition for a high porosity and a highly ordered pore structure in ordered mesoporous alumina film was determined. This alumina film maintained the mesoporous structure even though it annealed at high temperatures, up to 1200°C. Therefore, the ordered mesoporous alumina films synthesized in this study could be applicable as a material used at high temperature.

Keywords: PACS; 78.55.Mb porous materialsOrdered mesoporous Al; ₂; O; ₃; film; Aging time; Water; Pre-hydrolysis; High temperature annealing

Surface morphology of GaN nanorods grown by catalyst-free hydride vapor phase epitaxy by Yuri Sohn; Chinkyo Kim (pp. 1078-1081).

GaN nanorods were grown on c-plane sapphire substrates by using catalyst-free hydride vapor phase epitaxy (HVPE). The effects of substrate temperature, Ga boat temperature, and Ga pretreatment on the surface morphology of GaN nanorods were investigated. From the dependence of a radial and axial growth rate on the substrate temperature, the kinetically limited process was found to be a rate determining step in the growth of GaN nanorods in HVPE. In addition, the activation energy of the growth along the both axial and radial directions were estimated. The dependence of a Ga boat temperature and the Ga pretreatment effect revealed that the density of nanorods were dependent on the flux of Ga species on the substrate.

Keywords: PACS; 81.15.Kk; 68.55.−a; 68.37.HkGaN; Nanorods; Hydride vapor phase epitaxy

Change in work function during phase transition of Sc–O/W(100) system at high temperatures by Y. Nakanishi; T. Nagatomi; Y. Takai (pp. 1082-1087).

The change in work function during the phase transition of a Sc–O/W(100) system at high temperatures of 1500–1700K was investigated in order to elucidate the mechanism of the decrease in the work function of a (1×1)-Sc–O/W(100) surface. For the measurement of the work function using a secondary electron method at high temperatures, a sample holder was uniquely designed in order to suppress contributions of a large number of thermionic electrons emitted from a low-work-function surface. The obtained work function revealed that the change in work function strongly correlates with the coverage of Sc–O complexes, the stoichiometry of which is Sc₁O₁. The higher the coverage of ScO is, the lower the work function is, suggesting that the work function of the (1×1)-Sc–O/W(100) surface is reduced by the formation of ScO electric dipoles. Furthermore, the decrease in work function was modeled in combination with a previously reported kinetic model describing surface phenomena, i.e., the oxidation, oxygen desorption, diffusion and surface segregation of Sc–O complexes, during the phase transition of the Sc–O/W(100) surface at high temperatures. It was confirmed that the proposed model can explain the experimentally obtained change in work function very well. The value of the dipole moment of a ScO electric dipole was determined to be 2.7×10⁻³⁰Cm.

Keywords: Work function; High temperature; Sc–O/W(1; 0; 0) Schottky emitter; Phase transition; Scandium; Tungsten; Oxygen; Electric dipole

Binding energy shift in photoemission spectroscopy study of Ni clusters deposited on rutile TiO₂ surfaces by J.S. Pan; J.G. Tao; C.H.A. Huan; Z. Zhang; J.W. Chai; S.J. Wang (pp. 1088-1091).

Cluster-size-dependent binding energy (BE) shifts of Ni 2 p_3/2 spectra in Ni clusters with respect to bulk Ni metal have been studied as a function of Ni coverage on clean rutile TiO₂(001) surfaces at room temperature. Auger parameter (AP) analysis of photoelectron spectra has been employed and revealed an obvious initial state contribution at the coverage of 0.5 monolayers (ML). The initial state effect was demonstrated to be strongly affected by the substrate and was assigned to a combination of eigenvalue shift in surface core-level shift (SCLS) and charge transfer between the metal clusters and substrates. The TiO₂(001) surface stoichiometry was found to introduce different charge transfer behaviors. Our results experimentally present that the Ni clusters are charged positively on stoichiomtric TiO₂ surface and less positively or even negatively on various reduced surfaces.

Keywords: Photoelectron spectroscopy; Titanium oxide; Nickel; Cluster size effect

Anisotropy of magnetization-induced surface optical second harmonic generation from Co doped rutile TiO₂ by R. Watanabe; M. Tamura; Y. Yahata; G. Mizutani; T. Suzuki; Y. Segawa; Y. Matsumoto; Y. Yamamoto; H. Koinuma (pp. 1092-1095).

We have investigated the surface magnetization anisotropy of 5at% Co doped rutile TiO₂ (110) using magnetization-induced optical second harmonic generation (MSHG) in the longitudinal Kerr configuration with an incident beam angle of 4°. The MSH intensity pattern from the Co:TiO₂ without surface Co clusters showed two anisotropic lobes at the second harmonic photon energy of2ℏω=3.13eV. Since MSH intensity is proportional to surface magnetization, the result indicates an anisotropy of the surface magnetization of Co:rutile TiO₂ (110). This confirms the possibility that 5at% Co:rutile TiO₂ (110) is a ferromagnetic dilute magnetic semiconductor at its surface, as proposed in our previous paper.

Keywords: Magnetization-induced optical second harmonic generation (MSHG); Anisotropic surface magnetization; Co doped rutile TiO; ₂; (1; 1; 0)

Surface cleaning of metal wire by atmospheric pressure plasma by T. Nakamura; C. Buttapeng; S. Furuya; N. Harada (pp. 1096-1100).

In this study, the possible application of atmospheric pressure dielectric barrier discharge plasma for the annealing of metallic wire is examined and presented. The main purpose of the current study is to examine the surface cleaning effect for a cylindrical object by atmospheric pressure plasma. The experimental setup consists of a gas tank, plasma reactor, and power supply with control panel. The gas assists in the generation of plasma. Copper wire was used as an experimental cylindrical object. This copper wire was irradiated with the plasma, and the cleaning effect was confirmed. The result showed that it is possible to remove the tarnish which exists on the copper wire surface. The experiment reveals that atmospheric pressure plasma is usable for the surface cleaning of metal wire. However, it is necessary to examine the method for preventing oxidization of the copper wire.

Keywords: Atmospheric pressure discharge plasma; Plasma application; Surface cleaning; Annealing

Preparation of Titanium Oxide-containing Organic Film by Dipping Ti(OR)₄ and Cold Plasma oxidizing on PET by Ko-Shao Chen; Pei-Yu Liu; Tsui-Shan Hung; Shu-Chuan Liao; Su-Chen Chen; Hong-Ru Lin; Wei-Yu Chen; Chi-Kuang Feng (pp. 1101-1105).

Low temperature process to prepare titanium oxide film on the surface of PET was investigated in this study. The substrates were pre-treated by oxygen plasma activated procedure, and then spin coating of Ti(OR)₄ precursor solution was carried out to prepare Ti-containing organic films. Finally, O₂ plasma was employed to decompose organic compounds and oxidize Ti to form oxides. Oxygen plasma post treatment can oxidize the organic compounds to form titanium oxide carbon subsequently. From the IR and ESCA analysis could be observed that –CH bond decreases and Ti–O, C–O bonds increase after O₂ plasma treatment. Their surface hydrophilicity was enhanced by UV-irradiation, the degree of water contact angle decreased from 60° to 10°.

Keywords: Plasma; Surface modification; Ti

Cluster size dependence of SiO₂ thin film formation by O₂ gas cluster ion beams by T. Mashita; N. Toyoda; I. Yamada (pp. 1106-1109).

Cluster size effects of SiO₂ thin film formation with size-selected O₂ gas cluster ion beams (GCIBs) irradiation on Si surface were studied. The cluster size varied between 500 and 20,000molecules/cluster. With acceleration voltage of 5kV, the SiO₂ thickness was close to the native oxide thickness by irradiation of (O₂)_20,000 (0.25eV/molecule), or (O₂)_10,000 (0.5eV/molecule). However, it increased suddenly above 1eV/molecule (5000molecules/cluster), and increased monotonically up to 10eV/molecule (500molecules/cluster). The SiO₂ thickness with 1 and 10eV/molecule O₂-GCIB were 2.1 and 5.0nm, respectively. When the acceleration voltage was 30kV, the SiO₂ thickness has a peak around 10eV/molecule (3000molecules/cluster), and it decreased gradually with increasing the energy/molecule. At high energy/molecule, physical sputtering effect became more dominant process than oxide formation. These results suggest that SiO₂ thin film formation can be controlled by energy per molecule.

Keywords: PACS; 29.27.Fh; 36.40.Jn; 79.20.RfGas cluster ion beam; Cluster size; Thin film

Modification and smoothing of patterned surface by gas cluster ion beam irradiation by T. Hirota; N. Toyoda; A. Yamamoto; I. Yamada (pp. 1110-1113).

Surface modification and smoothing of patterned surfaces with gas cluster ion beams were studied. In this work, line and space patterns having various intervals and depths were created on amorphous carbon films by focused Ga⁺ ion beams, and subsequently, Ar GCIB irradiations on the pattern were performed. When the acceleration voltage of Ar cluster ions was 20kV, the grooves, whose interval was below 200nm, were planarized. However, it required much higher ion dose for wider interval of patterns. It is estimated that the distance of lateral motions induced by one cluster ion impact defines the spatial wavelength dependence of smoothing.

Keywords: PACS; 07.77+p; 79.20.Rf; 81.65.CfGCIB; Surface smoothing; Patterned surface

Adsorption, reaction and desorption of hydrogen on modified Pd(111) surfaces by Adolf Winkler (pp. 1114-1119).

The interaction of hydrogen (deuterium) with different modified Pd(111) surfaces has been investigated. The focus was put on the energy and angel dependence of the desorbing molecules from oxygen covered, potassium covered and vanadium oxide covered surfaces. Conventional adsorption/desorption as well as permeation/desorption experiments were performed. For the oxygen covered surface optimum reaction rates for water production and the energy distribution of the reaction products were determined, both for the reaction of oxygen with molecular hydrogen as well as with atomic hydrogen. Potassium on the surface enhances the activation barrier for hydrogen adsorption resulting in a hyper-thermal desorption flux and a forward focused angular distribution of desorption. Permeation/desorption of deuterium from ultra-thin vanadium oxide films yield mainly thermalized desorbing molecules or slightly hyper-thermal, depending on the oxidation state of the surface oxide.

Keywords: PACS; 68.43.Mn; 68.43.Nr; 68.47.De; 68.47.GhAdsorption; Desorption; Permeation; Hydrogen; Palladium; Kinetics; Dynamics

The2×2 oxidized layer on ZrB₂(0001) by Takashi Aizawa; Shunichi Hishita; Shigeki Otani (pp. 1120-1123).

Initial oxidation of a ZrB₂(0001) surface at high temperature yields a new2×2 ordered surface structure, as characterized using reflection high-energy electron diffraction (RHEED), Auger electron spectroscopy (AES), high-resolution electron energy loss spectroscopy (HREELS), and X-ray photoelectron spectroscopy (XPS). During high-temperature treatment in O₂, the surface becomes boron-deficient. In the surface oxide layer, Zr is not fully oxidized, but in a Zr³⁺ state. The HREELS shows strong loss peaks, showing insulating characteristics of the surface.

Keywords: PACS; 68.35.Np; 68.43.Fg; 79.60.DpTransition-metal diboride; Oxidation; Surface structure

Crystallization of D₂O thin films on Ru(001) surfaces by T. Yamauchi; K. Mine; Y. Nakashima; A. Izumi; A. Namiki (pp. 1124-1127).

The phase conversion of amorphous solid water (ASW) to crystalline ice (CI) has been investigated in the very thin (∼10 monolayers) film regime on a Ru(001) surface. We analyze the converted CI fraction with the Avrami model, and recognize that one-dimensional CI growth occurs, which can be contrasted to the three-dimensional CI growth generally established in the thick (≥50 monolayers) film regime. We evaluate activation energy for the ASW crystallization to be about 1.0eV. We suggest that the ASW crystallization is not influenced by the substrate even near the substrate–ice interface.

Keywords: PACS; 33.20.Ea; 87.15.ntRuthenium; Crystallization; Amorphous solid water; Infrared spectrum

Transformation of cluster structure at initial stage by T.Y. Fu; Y.H. Wang; T.T. Tsong (pp. 1128-1131).

The initial stages of cluster nucleation for Pd or Ir adatoms on a W (110) surface and in the vicinity of surface steps are directly imaged by a field ion microscope (FIM). Three types of structures are observed. One is a one-dimensional linear chain, which is parallel to the nearest neighbor-stacking directions of the substrate. Another is a two-dimensional compact island, which is a pseudomorphic structure like the substrate. The other is a three-dimensional cluster, which shows a structural transition from bcc (110) to fcc (111). Factors affecting the structural transformation include coverage of atoms or atom chains, temperature of heat treatments and boundary of the substrate terrace.

Keywords: Field ion microscopy; Nucleation; Surface thermodynamics; Structural transformation

Adsorption of cobalt phthalocyanine on a Si(100) surface with Bi-line structures as evaluated by scanning tunneling microscopy by T. Ikari; S. Tanaka; S. Nakamura; M. Naitoh; S. Nishigaki; F. Shoji (pp. 1132-1135).

We report the reaction dynamics of cobalt phthalocyanine (CoPc) molecules with Bi-line structures (BLSs) on a Si(100) surface, investigated using scanning tunneling microscopy (STM). When CoPc molecules were deposited on a Si(100) surface with BLSs at room temperature, single-spot protrusions were observed in the STM image instead of four-spot images corresponding to CoPcs flat molecular structure. Moreover, domains with a c(4×4) periodicity appeared on the terraces of the Si(100) surface. This indicates that CoPc molecules may have decomposed on the surface by catalytic reaction with Bi atoms.

Keywords: PACS; 68.37.Ef; 68.43.HnSTM; Bismuth; Si(1; 0; 0) surface; Surface structure; Phthalocyanine

Indium-induced superstructures formed on Si(110) surfaces by Toshihiro Ichikawa; Takeshi Waragaya (pp. 1136-1139).

Si(110) surfaces covered with small amounts of In deposit and then annealed at high temperature were investigated by RHEED, and two kinds of superstructures withA=3a andB=−a+4b, andA=3a−2b andB=−2a+4b as primitive translational vectors are reported to form on the surfaces.

Keywords: PACS; 61.14.Hg; 68.37.Ef; 68.43.Fg; 68.47.FgSi(1; 1; 0); RHEED; Superstructure; Indium

Adsorption structure of phenylphosphonic acid on an alumina surface by Shinjiro Yagyu; Michiko Yoshitake; Nataliya Tsud; Toyohiro Chikyow (pp. 1140-1143).

The adsorption structure of phenylphosphonic acid (PPOA) on an alumina surface was investigated as a function of exposure and temperature using infrared reflected absorption spectroscopy (IRAS) and a Kelvin probe. The alumina surface was held at room temperature during deposition. At monolayer adsorption, PO and Phenyl-P bands are observed, which indicate the creation of POAl bonds. The aromatic ring plane is positioned perpendicular to the surface, i.e. deprotonated PPOA stands vertically on the surface. At multilayer adsorption, PO and POH bands appear in the spectra. The multilayer PPOA film starts to desorb at 400K. From 400 to 700K, the IRAS spectra are similar to the monolayer spectrum, indicating that the multilayer structure reverses to the monolayer-like PPOA adlayer by heating. The acid molecules start to desorb at 700K.

Keywords: PACS; 68.43.Fg Adsorbate structure (binding sites; geometry)Work function; Alumina; Phenylphosphonic acid; Adsorption

In situ observation of a Au (111) electrode surface using the X-ray reciprocal-lattice space imaging method by Osami Sakata; Masashi Nakamura (pp. 1144-1147).

A rapid X-ray diffraction method was proposed for in situ observation of a surface-intermediate structure on a liquid–solid interface. It used a combination of higher-energy monochromatic synchrotron X-rays in grazing incidence and an X-ray two-dimensional detector. Overall patterns were in situ taken, with one-time exposure, of the reciprocal-lattice space of a Au (111) electrode surface which was fixed at an angular position. We deduced change in crystal domain shapes of surface intermediates as well as its smaller lattice distortion by observing images of reconstructed surface rods during a surface-structural phase transition from the reconstructed surface to the bulk terminated surface. An anisotropic shape of surface-crystal domains was also observed.

Keywords: PACS; 61.10.Kw; 68.08.; −; p; 68.47.DeReciprocal-lattice space imaging; Buried interface; In situ X-ray diffraction; Surface structural change during surface phase transition; Surface structure; Gold

Size-selected Au clusters deposited on SiO₂/Si: Stability of clusters under ambient pressure and elevated temperatures by Dong Chan Lim; Rainer Dietsche; Gerd Ganteför; Young Dok Kim (pp. 1148-1151).

This study examined the oxidation and reduction behavior of mass-selected Au clusters consisting of 2–13 atoms deposited on silica. An atomic oxygen environment was used for the oxidation of Au. X-ray photoelectron spectroscopy (XPS) was used to identify Au(III) and Au(O). Au₅, Au₇ and Au₁₃ clusters deposited on the as-prepared SiO₂/Si substrates were highly inert towards oxidation, whereas the other clusters could be oxidized, i.e. the chemical property drastically changed with the number of atoms in a cluster. The size-selectivity in chemical reactivity remained unchanged upon air-exposure. The chemical properties of the deposited Au clusters were unchanged after annealing at 250°C. Annealing at higher temperatures caused structural changes to the surface, as determined by the oxidation behavior. XPS of the deposited Au clusters upon annealing indicated charge transfer from Au to silica.

Keywords: Au; SiO; ₂; Mass-selected clusters; Oxidation

Fabrication and scanning tunneling microscopy studies of the Si(111)-(√31×√31)–In surface by Zheng Wei; Heechul Lim; Geunseop Lee (pp. 1152-1155).

We report on the fabrication of single phase of the Si(111)-(√31×√31)–In reconstruction surface, observed by scanning tunneling microscopy (STM) at room temperature. By depositing specific amounts of indium atoms while heating the Si(111)-(7×7) substrate at a critical temperature, the single phase of Si(111)-(√31×√31)–In surfaces could be routinely obtained over the whole surface with large domains. This procedure is certified by our high-resolution STM images in the range of 5–700nm. Besides, the high resolution STM images of the Si(111)-(√31×√31)–In surface were also presented.

Keywords: PACS; 68.37.Ef; 68.43.Fg; 68.47.FgScanning tunneling microscopy; Si(1; 1; 1)-(√31; ×; √31)–In; Fabrication

Electronic structure of dysprosium silicide films grown on a Si(111) surface by Ayako Imai; Haruya Kakuta; Kenji Mawatari; Ayumi Harasawa; Nobuo Ueno; Taichi Okuda; Kazuyuki Sakamoto (pp. 1156-1159).

The thickness-dependent electronic structures of Dy silicide films grown on a Si(111) surface have been investigated by angle-resolved photoelectron spectroscopy. Two (1×1) periodic bands, both of them cross the Fermi level, have been observed in the silicide films formed by Dy coverages of 1.0 monolayer and below, and more than five (3×3) periodic bands have been observed in thicker films. Taking the (23×23) periodic structure of Dy atoms in the submonolayer silicide film into account, the periodicity of the two metallic bands indicate that they mainly originate from the orbitals of Si atoms, which form a (1×1) structure. Of the (3×3) periodic bands observed in thick films, four of them are well explained by the folding of the (1×1) bands into a (3×3) periodicity. Regarding the other band, the three (3×3) periodic bands would originate from the electronic states related to the inner Si layers that form a (3×3) structure, and the one observed in the 3.0ML film only might originate from the electron located at the interface between bulk Si and the Dy silicide film.

Keywords: PACS; 73.20.At; 79.60.; −; i; 61.05.JhElectronic structure; Rare-earth silicide; Angle-resolved photoelectron spectroscopy; Low-energy electron diffraction

Systematic theoretical investigation for adsorption behavior of Al and N atoms on 4H–SiC(112¯0) surfaces by Takumi Ito; Toru Akiyama; Kohji Nakamura; Tomonori Ito (pp. 1160-1163).

We systematically investigate adsorption behavior of Al and N atoms on 4H–SiC (112¯0) surfaces based on first-principles calculations. The calculations for stable adsorption site demonstrate that the Al atom is adsorbed at the lattice site of 4H structure whereas the N atom is incorporated at the interstitial site. The calculated surface phase diagrams for Al and N atoms as functions of beam equivalent pressure and temperature clarify that Al atoms can be adsorbed at all of the adsorption sites below 1800K and N atoms, in contrast, are desorbed excepting the most stable site above 1150K. These temperatures imply that under experimental conditions (1223K) Al atoms can be easily adsorbed and N atoms are adsorbed only on the most stable adsorption site. Furthermore, the calculated barrier heights of adsorbed Al and N atoms are 1.0 and 1.8eV, respectively, implying that the surface migration of Al atoms is prominent compared to that of N atoms. These results obtained thus manifest that adsorption behavior of Al and N atoms is quite different and the growth processes change depending on V/III ratio under molecular beam epitaxy growth.

Keywords: Nonpolar surface; AlN; SiC; Ab initio; calculation; Adsorption; Desorption

An ab initio-based approach to adsorption–desorption behavior of Si adatoms on GaAs(111) A–(2×2) surfaces by Hiroaki Tatematsu; Toru Akiyama; Kohji Nakamura; Tomonori Ito (pp. 1164-1167).

The adsorption–desorption behavior of Si adatoms on GaAs(111) A–(2×2) surfaces is investigated using our ab initio-based approach, in which adsorption and desorption behavior of Si adatoms is described by comparing the calculated desorption energy obtained by total-energy electronic-structure calculations with the chemical potential estimated by quantum statistical mechanics. We find that the Si adsorption at the Ga-vacancy site on the (2×2) surfaces with As adatoms occurs less than 1140–1590K while the adsorption without As adatom does less than 630–900K. The change in adsorption temperature of Si adatoms by As adatoms is due to self-surfactant effects of As adatoms: the promotion of the Si adsorption triggered by As adatoms is found to be interpreted in terms of the band-energy stabilization. Furthermore, the stable temperature range for Si adsorbed surfaces with As adatoms agrees with the experimental results. The obtained results provide a firm theoretical framework to clarify n-type doping processes during GaAs epitaxial growth.

Keywords: PACS; 61.72.Vv; 68.47.Fg; 81.05.EaGaAs(1; 1; 1); A; Si doping; As adatom; Self-surfactant effect; Electron counting; Surface phase diagram

Si islands with 1×1 termination formed by desorption of Tl from Si(111) surface by P. Kocán; H. Tochihara (pp. 1168-1170).

We report on the scanning tunneling microscopy observation of small Si islands with a 1×1 termination on the Si(111) surface. The islands were prepared by thermal desorption of Tl from the Tl-terminated silicon sample by means of annealing to 400–600°C. Structure of the islands is interpreted as the dimer-stacking-fault (DS) model. We propose that the otherwise unfavorable 1×1 termination is stabilized by subsurface dimers of DS.

Keywords: Scanning tunneling microscopy; Silicon; Thallium; Si(1; 1; 1)

Study on contamination of projection optics surface for extreme ultraviolet lithography by Keigo Koida; Masahito Niibe (pp. 1171-1175).

Ru-capped Mo/Si multilayer mirrors were irradiated by EUV in a vacuum atmosphere with ethanol or decane gas, and their reflectivity changes by contamination were investigated by changing the amount of introduced gas. The reflectivity hardly decreased by EUV irradiation in the ethanol-introduced atmosphere. On the other hand, the reflectivity decreased by about 5% in the decane-introduced atmosphere at a decane pressure of P_Decane=1.3×10⁻⁴Pa, an EUV power of about 200mW/mm², and an EUV dose of 150J/mm². EUV irradiation to the Ru-capped multilayer mirrors was also performed in the presence of water vapor and decane. The surface oxidation by EUV irradiation with a water vapor pressure ofPH2O=1.3×10−5Pa was controlled by the introduction of decane at a pressure of P_Decane=7.0×10⁻⁷ to 1.3×10⁻⁶Pa.

Keywords: EUVL; Contamination; Multilayer mirror; Ru; Carbon deposition; Lifetime acceleration test

Observation of coexistence of 1D and 2D nanostructures in cobalt dipyrromethene trimer complexes adsorbed on a graphite surface by S.B. Son; S.J. Lee; J.R. Hahn; L. Ma; J.-Y. Shin; D. Dolphin (pp. 1176-1179).

We report the direct observation of 1D and 2D nanostructures of cobalt dipyrromethene trimer complexes adsorbed on a highly oriented pyrolytic graphite surface using scanning tunneling microscopy (STM). STM images showed two types of ordered structures coexisting on the surface: long 1D molecular chains isolated on the terraces, and 2D hexagonal patterns confined by a 1D chain and/or a graphite step edge. These 1D and 2D structures are attributed to ‘edge-on’ and ‘face-on’ complex alignments on the surface, respectively. In both configurations, substrate-mediated molecule–molecule interactions may play a significant role in stabilizing the nanostructures.

Keywords: PACS; 68.37.Ef, 81.16.Fg, 64.75.Yz, 81.07.NbScanning tunneling microscopy; Dipyrromethene; Graphite; Supramolecules; Porphyrin

Zn1−_xMg_xO/ZnO heterostructures studied by Kelvin probe force microscopy conjunction with probe characterizer by Te-Wei Chiu; Hiroshi Itoh; Hitoshi Tampo; Shigeru Niki (pp. 1180-1183).

The surface potential of Zn1−_xMg_xO/ZnO heterostructure grown by radical source molecular beam epitaxy was measured by Kelvin force microscopy (KFM). A clear correlation was observed between the topographic image and the surface potential of Zn_0.56Mg_0.44O/ZnO heterostructure. The potential area around the surface pits was about 60mV lower than that of the surrounding region, which suggests the effects of the pits on the electrical properties of the potential layer. In order to guarantee the accuracy of measurement, the probe shape was analyzed by probe characterizer and using Au thin films as a potential standard.

Keywords: Kelvin force microscopy; Probe characterizer; ZnMgO; ZnO; Surface potential

MeV-ion axial surface-channeling from an electron irradiated KCl(001) surface by Yuuko Fukazawa; Yuugo Matsumoto; Kei Mitsuhara; Yasufumi Susuki (pp. 1184-1190).

Surface-channeling of protons incident with 5mrad on an electron-irradiated surface is investigated using a 0.55MeV beam of protons. The target surface is KCl(001), which is damaged by electron-stimulated desorption with 5keV electron irradiation. The direction of the incident beam is adjusted along the 〈100〉 and 〈110〉 channeling conditions and the channeling-dips of the scattering yields are observed. The irradiation dose-dependence of the minimum yields and widths of the dips is measured. Two dips are compared, i.e., for the 〈100〉 and 〈110〉 channelings. By increasing the irradiation dose up to 2×10¹⁶cm⁻², the dip around the 〈100〉 axis becomes opened, but that of the 〈110〉 axis becomes shallow. The irradiated surfaces are observed to have many overlapped terraces of sub-micron with monolayer steps. The surface morphology deformed by the irradiation effects to truncate trajectories of the 〈100〉 channeling protons. This roughness of the surface is more effective for the trajectories of the 〈110〉 channeling protons. The protons incident on the rough surface along the 〈110〉 axis are not reflected from the atomic row but reflected by a potential of the surface with steps. Results by a simple computer simulation of the trajectories of protons at stepped surfaces also indicate the scattering processes.

Keywords: Surface-channeling; Ionic crystal; Electron-stimulated desorption; Atomic force microscope

Modification by H-termination in growth process of titanium silicide on Si(001)-2×1 observed with scanning tunneling microscopy by T. Aoki; K. Shudo; K. Sato; S. Ohno; H. Nishioka; T. Iida; M. Toramaru; M. Tanaka (pp. 1191-1195).

Formation processes of titanium silicide on hydrogen-terminated H/Si(001)-2×1 surface are studied at the atomic scale with a scanning tunneling microscopy (STM). Square-shaped nanoislands were observed on the Ti/H/Si(001) surface after annealed at 873–1073K. These are the epitaxial nanoislands moderately grown due to the local orientation relationship between C49–TiSi₂ and Si(001), because passivation by surface hydrogen on Si(001) suppresses active and complex bond formation of Ti–Si.

Keywords: Silicide; Ti; Surface; STM; Hydrogen

Electron-stimulated defect formation in single-walled carbon nanotubes studied by hydrogen thermal desorption spectroscopy by Satoshi Arima; Sangkil Lee; Yutaka Mera; Shohei Ogura; Katsuyuki Fukutani; Yoshinori Sato; Kazuyuki Tohji; Koji Maeda (pp. 1196-1199).

Defects in single-walled carbon nanotubes introduced by low-energy electron irradiation at 8K were sensitively detected by cryogenic thermal desorption of hydrogen molecules H₂ in the temperature range of 10–40K. The thermal desorption spectrum was found to change significantly with sample annealing at temperatures as low as 40–70K. Experimental results suggest that the H₂ physisorption sites responsible for the ‘defect’ peak at 28K are interstitial channel space between nanotubes closely packed in bundles which becomes more easily accessible on damage. It is also suggested that the disordering provides groove sites for H₂ physisorption with smaller binding energy causing the damage-induced spectral component around 16K, slightly lower than the desorption peak at 20K that is observed in undamaged samples. The spectral change at 40–70K could be interpreted by migration of adatoms at the low temperatures.

Keywords: Carbon nanotube; Defect; Electron irradiation; Thermal desorption; Hydrogen; Physisorption; Electronic excitation

Inelastic mean free path, surface excitation parameter, and differential surface excitation parameter in Au for 300–3000eV electrons by T. Nagatomi; K. Goto (pp. 1200-1204).

An analytical approach for simultaneously determining an inelastic mean free path (IMFP), a surface excitation parameter (SEP) and a differential SEP (DSEP) with absolute units was applied for the analysis of absolutely measured reflection electron energy loss spectra for Au. The IMFP, SEP and DSEP in Au for 300–3000eV electrons are successfully obtained. The obtained DSEPs show a reasonable agreement with those theoretically calculated. The present SEPs were compared with those calculated by several empirical equations, revealing that the present SEPs are close to those calculated using the Oswald's equation. The IMFPs for Au determined by the present analysis were compared with those calculated by the TPP-2M predictive equation, revealing that the present IMFPs are in fairly good agreement with those calculated by the TPP-2M equation. The results confirmed that the present approach is effective for experimentally determining the SEP, DSEP, and IMFP for electrons in solids.

Keywords: PACS; 82.80.Pv; 79.20.−m; 79.20.Uv; 73.20.MfReflection electron energy loss spectroscopy; Inelastic mean free path; Surface excitation parameter; Bulk excitation; Surface excitation

Thermal step bunching on the restricted solid-on-solid model with point contact inter-step attractions by Noriko Akutsu (pp. 1205-1209).

We present the restricted solid-on-solid (RSOS) model with the inter-ledge interaction of the point contact type (p-RSOS model). We have made detailed calculation of the Andreev free energyf˜(ηx,ηy), which is similar to the equilibrium crystal shape (ECS)z=z(x,y), and the surface gradientp→=(px,py)=(∂z/∂x,∂z/∂y) as the function of the Andreev fieldη→. From the calculatedf˜(ηx,ηy) andp→(η→), we have obtained the vicinal surface free energyf(p→). The inter-ledge attraction between adjacent steps affects the surface free energies in the equilibrium, and causes the first-order transition on the profile of ECS at low temperature. The inter-ledge attraction also destabilizes the regular train of steps. We also have obtained the thermal step bunching.

Keywords: PACS; 68.35.Md; 05.70.Np; 05.50.+q; 68.35.−pSurface free energy; DMRG calculations; Equilibrium crystal shape; ECS; The first-order transition; Self-organization

Atomic level analysis of biomolecules by the scanning atom probe by Osamu Nishikawa; Masahiro Taniguchi; Atsushi Ikai (pp. 1210-1213).

Utilizing the unique features of the scanning atom probe (SAP) the binding states of the biomolecules, leucine and methionine, are investigated at atomic level. The molecules are mass analyzed by detecting a single atom and/or clustering atoms field evaporated from a specimen surface. Since the field evaporation is a static process, the evaporated clustering atoms are closely related with the binding between atoms forming the molecules. For example, many thiophene radicals are detected when polythiophene is mass analyzed by the SAP. In the present study the specimens are prepared by immersing a micro cotton ball of single walled carbon nanotubes (SWCNT) in the leucine or methionine solution. The mass spectra obtained by analyzing the cotton balls exhibit singly and doubly ionized carbon ions of SWCNT and the characteristic fragments of the molecules, CH₃, CHCH₃, C₄H₇, CHNH₂ and COOH for leucine and CH₃, SCH₃, C₂H₄, C₄H₇, CHNH₂ and COOH for methionine.

Keywords: Scanning atom probe; Single walled carbon nanotubes; Field evaporation; Fragment ions; Leucine; Methionine

Evaluations of carbon nanotube field emitters for electron microscopy by Hitoshi Nakahara; Yoshikazu Kusano; Takumi Kono; Yahachi Saito (pp. 1214-1217).

Brightness of carbon nanotube (CNT) emitters was already reported elsewhere. However, brightness of electron emitter is affected by a virtual source size of the emitter, which strongly depends on electron optical configuration around the emitter. In this work,I–V characteristics and brightness of a CNT emitter are measured under a practical field emission electron gun (e-gun) configuration to investigate availability of CNT for electron microscopy. As a result, it is obtained that an emission area of MWNT is smaller than its tip surface area, and the emission area corresponds to a five-membered-ring with 2nd nearest six-membered-rings on the MWNT cap surface. Reduced brightness of MWNT is measured as at least2.6×109A/m²srV. It is concluded that even a thick MWNT has enough brightness under a practical e-gun electrode configuration and suitable for electron microscopy.

Keywords: PACS; 85.35.Kt; 29.25.Bx; 85.45.DbCarbon nanotube (CNT); Point electron source; Field emission; Brightness

Systematic theoretical investigations for contribution of lattice constraint to novel atomic arrangements in alloy semiconductor thin films by Tomonori Ito; Naoki Takasu; Toru Akiyama; Kohji Nakamura (pp. 1218-1221).

The atomic arrangements in zinc blende structured GaN_xAs1−_x thin films coherently grown on V-grooved substrates are theoretically investigated using empirical interatomic potentials and Monte Carlo simulation. The resultant atomic arrangements in GaN_xAs1−_x strongly depend on concentration x and substrate lattice parameter a_sub. Surface segregation of As or N is mainly found in GaN_xAs1−_x with large lattice mismatch to the substrate. On the other hand, the novel atomic arrangements such as layered segregation or ordered structure are found in GaN_xAs1−_x at the specific region such as ( x, a_sub)=(0.5, 5.3), (0.3, 5.3), and (0.3, 5.1). This specific region corresponds to that with negative excess energy and with sufficient N and As atoms remaining in thin film layers even after their surface segregation. The formation of the novel atomic arrangements is discussed in terms of bond lengths in the surface layers. These results suggest that various novel atomic arrangements in alloy semiconductor thin films appear depending on x and a_sub which control degree of lattice constraint.

Keywords: PACS; 61.66.Dk; 68.55.Jk; 31.15.CtGaN; _x; As; 1−; _x; thin films; V-grooved substrate; Lattice constraint; Layered segregation; Surface segregation; Empirical interatomic potential

Low temperature deposited Zr–B film applicable to extremely thin barrier for copper interconnect by Mayumi B. Takeyama; Atsushi Noya; Yasuo Nakadai; Shozo Kambara; Masanobu Hatanaka; Yuichiro Hayasaka; Eiji Aoyagi; Hideaki Machida; Kazuya Masu (pp. 1222-1226).

We have prepared thin Zr–B films at low temperatures as a new material applicable to an extremely thin barrier against Cu diffusion in Si-ULSI metallization. The obtained Zr–B films mainly consist of the ZrB₂ phase with a nanocrystalline texture on SiO₂ and a fiber texture on Cu. The resistivity of the Zr–B films depends on the substrate of SiO₂ or Cu. The constituent ratio of B/Zr is almost 2, though the contaminants of oxygen, nitrogen, and carbon are incorporated in the film. The nanocrystalline structure of the Zr–B film on SiO₂ is stable due to annealing at temperatures up to 500°C for 30min. We applied the 3-nm thick Zr–B film to a diffusion barrier between Cu and SiO₂, and the stable barrier properties were confirmed. We can demonstrate that the thin Zr–B film is a promising candidate for thin film application to a metallization material in Si-ULSIs.

Keywords: Cu interconnect; Diffusion barrier; ZrB; ₂; Nanocrystalline

Surface morphology and luminescence characterization of β-FeSi₂ thin films prepared by pulsed laser deposition by M. Zakir Hossain; Tomohiro Mimura; Noboru Miura; Shin-ichiro Uekusa (pp. 1227-1231).

β-FeSi₂ thin films were prepared on Si (111) substrates by pulsed laser deposition (PLD) with a sintering FeSi₂ target and an electrolytic Fe target. The thin films without micron-size droplets were prepared using the electrolytic Fe target; however, the surface without droplets was remarkably rougher using the Fe target than using the FeSi₂ target. After deposition at 600°C and then annealing at 900°C for 20h, XRD indicated that the thin film prepared using the Fe target had a poly-axis-orientation, but that prepared using the FeSi₂ target had a one-axis-orientation. The PL spectra of the thin films prepared using the FeSi₂ and Fe targets at a growth temperature of 600°C and subsequently annealed at 900°C for 20h had A-, B- and C-bands. Moreover, it was found that the main peak at 0.808eV (A-band) in the PL spectrum of the thin films prepared using the FeSi₂ target was the intrinsic luminescence of β-FeSi₂ from the dependence of PL peak energy on temperature and excitation power density.

Keywords: PACS; 78.66.Li; 61.30.Pq; 81.16.Mk; 78.55.−mβ-FeSi; ₂; Droplet; Pulsed laser deposition; Photoluminescence

AlF₃ film deposited by IAD with end-Hall ion source using SF₆ as working gas by Huang-Lu Chen; Jin-Cherng Hsu; Paul W. Wang; Yung-Hsin Lin; Kung-Tung Wu; Chi-Ren Liu (pp. 1232-1235).

A novel and effective process to fabricate high quality fluoride thin films was presented. Aluminum fluoride films deposited by a conventional thermal evaporation with an ion-assisted deposition (IAD) using SF₆ as a working gas at around room temperature were investigated. In this study, the optimal voltage and current, 50V and 0.25A, were found according to the optical properties of the films: high refractive index (1.489 at 193nm), low optical absorption and extinction coefficient (<10⁻⁴ at 193nm) in the UV range. The physical properties of the film are high packing density and amorphous without columnar structure. It was proved that using SF₆ working gas in IAD process is a good choice and significantly improves the quality of AlF₃ films.

Keywords: PACS; 68.55.J−; 78.66.−w; 68.55.−a; 81.15.Aa; and 68.55.jmIon-assisted deposition; IAD; AlF; ₃; Fluoride; Sulfur hexafluoride; End-Hall ion source

Surface plasmon resonance detection using amorphous carbon/Au multilayer structure by Hiroki Akasaka; Naoki Gawazawa; Shin-ichi Kishimoto; Shigeo Ohshio; Hidetoshi Saitoh (pp. 1236-1239).

Surface plasmon resonance (SPR) can be used to detect the change in reflective index on a metal surface. In this report, we propose detection of the SPR can easily be applied to estimate the thickness of the amorphous carbon ( a-C:H) films. To detect changes in film thickness using SPR, devices with an a-C:H/Au structure were fabricated. The a-C:H films were deposited by electron cyclotron resonance plasma chemical vapor deposition (ECR-CVD) and sputtering, and the obtained film densities were 1.4 and 1.6g/cm³, respectively. By the deposition of an 11-nm thick a-C:H film on a Au layer by sputtering, the SPR angle changed from 44.90° to 47.05°. For a-C:H deposited by ECR-CVD, the SPR angle was shifted from 44.24° for Au without the a-C:H layer to 58.44° after deposition of 45nm thick a-C:H film. In both systems of the SPR angle increased with increasing the film thickness. The rate at which the SPR angle shifted depended on the a-C:H film density. These results show that the thickness of an a-C:H film can be determined by the SPR angle shift on an a-C:H layer using a-C:H/Au device with an a-C:H film of the same density.

Keywords: Amorphous carbon; Surface plasmon resonance; Multilayer structure

Copper filling of deep sub-μm through-holes by high-vacuum planar magnetron sputtering using argon gas with added oxygen by Yoshio Uhara; Tsubasa Urano; Masatoshi Itoh; Hideo Hayashi; Yousuke Manba; Akifumi Taniseki; Houin Jyan; Eiichi Nishikawa; Sigeru Saito (pp. 1240-1243).

Changes in filling characteristics when adding oxygen to sputtering gas (1at.%N₂–Ar) were investigated using high-vacuum planar magnetron sputtering equipment having little residual gas effects. It was found that copper filling accelerates for oxygen partial pressure in sputtering gas ofPO2=5×10−5to1×10−4Pa and a substrate temperature of 300–320°C. Under these conditions, 70% copper filling in fine holes of diameter ϕ=100nm (AR=4.5) was obtained.

Keywords: PACS; 85.40.LsCopper filling; Added oxygen; Planar magnetron sputtering; Fine holes; Reflow method

Iron disilicide formation by Au–Si eutectic reaction on Si substrate by Kensuke Akiyama; Satoru Kaneko; Kazuya Yokomizo; Masaru Itakura (pp. 1244-1248).

We have investigated the growth of iron disilicide on Au-coated Si(001) substrates and its photoluminescence behaviour. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy observations revealed that the Si surface above 380°C was melted as a result of the Au–Si eutectic reaction and that coarse island disilicide grains with sizes of several micrometres were formed on the Si surface. The full width at half maximum of 0.056° on the rocking curve of α-FeSi₂ 004 was observed on the sample deposited at 800°C, and indicated the high crystal quality in perfection of orientation. The photoluminescence spectrum of β-FeSi₂ grains, which were deposited at 750°C, was observed. The melted Si surface contributed to the improved crystallinity of α-FeSi₂ and β-FeSi₂.

Keywords: PACS; 81.05.Je; 81.10.Bk; 81.40.−zIron disilicide; Crystal growth; Microstructure

Spin-spiral and domain wall structures in monolayer Fe/W(110) by Kohji Nakamura; Toru Akiyama; Tomonori Ito (pp. 1249-1251).

The stability of spin-spiral and domain wall structures in an Fe monolayer on a W(110) substrate is theoretically investigated. By analyzing the exchange parameters obtained from first principles total energy calculations, we find that a competition between the nearest-neighbor ferromagnetic and long-distant antiferromagnetic exchange interactions leads to a stabilization of the spin-spiral structures. When the strong magnetocrystalline anisotropy (MCA) arising from the Fe/W(110) interface is introduced, however, the formation of the spin-spiral structures is suppressed and the ground state appears to be the ferromagnetic state—as observed in experiments. In addition, the strong MCA is found to play a key role in determining the domain wall structures.

Keywords: PACS; 75.70.Ak; 75.60.ChSpin-spiral structures; Domain wall structures; Monolayer Fe/W(1; 1; 0); First principles calculations

Epitaxial growth of Bi thin films on Ge(111) by Shinichiro Hatta; Yoshiyuki Ohtsubo; Sanae Miyamoto; Hiroshi Okuyama; Tetsuya Aruga (pp. 1252-1256).

We investigated Bi thin film growth on Ge(111) by using low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). In the submonolayer regime, adsorbed Bi atoms form patches of the(2×1) structure. However, the structure does not grow to a long-range order. Following the formation of a(1×1) monolayer (ML) film, two-dimensional (110)-orientated Bi islands grow. The film orientation changes from (110) to (111) at 6–10ML. The (110)-oriented Bi film shows a six-domain LEED pattern with missing spots, associated with a glide-line symmetry. The hexagonal (111) film at 14ML has a lattice constant 2% smaller than bulk Bi(111).

Keywords: Low-energy electron diffraction; Scanning tunneling microscopy; Thin film growth; Bismuth; Ge(1; 1; 1)

Bi surfactant effects of Co/Cu multilayered films prepared by sputter deposition by Masao Kamiko; Atsuhito Nakamura; Kazuaki Aotani; Ryoichi Yamamoto (pp. 1257-1260).

The influence of a Bi surfactant layer on the structural and magnetic properties of Co/Cu multilayers grown onto Cu(110) buffer layer by RF magnetron sputtering has been studied. The results of X-ray diffraction revealed the initial deposition of a 2.0Å-thick Bi layer onto the Cu buffer layer prior to the deposition of the Co/Cu multilayer yielded high-quality fcc-(110) oriented epitaxial films. The X-ray photoelectron spectra revealed that Bi was segregated at around the top of the surface. Therefore, Bi was concluded to be an effective surfactant to enhance the epitaxial growth of Co/Cu(110) multilayer. The maximum giant magnetoresistance and antiferromagnetic interlayer coupling ratios of the Co/Cu multilayers were increased by using the Bi surfactant layer.

Keywords: PACS; 68.55.jk; 75.47.De; 81.15.CdSurface segregation; Surfactant; Epitaxy; Metallic multilayers; Sputtering; Giant magnetoresistance

Impact of ZnTe buffer on the electrical properties of n-type GaSb:Te films by Siyoung Kim; Woong Lee; Mina Jung; Jiho Chang; Aung Khaing Nyi; Hongchan Lee; Joonsuk Song; Dongcheol Oh; Seunghwan Park; Takafumi Yao (pp. 1261-1264).

We have investigated on the molecular beam epitaxy (MBE) of Te-doped GaSb films on ZnTe buffer. Te-doped GaSb (GaSb:Te) films with and without ZnTe buffer were grown on (001) GaAs substrates. GaSb:Te/ZnTe/GaAs film revealed higher mobility (=631cm²/Vs) in comparison to GaSb:Te/GaAs film (=249cm²/Vs). To explain the higher mobility of GaSb:Te on ZnTe buffer, dislocation density and temperature dependence of Hall measurement results were analyzed. Temperature dependence of Hall measurement shows strong influence of the dislocation scattering, which indicates that dislocation reduction by the ZnTe buffer enhances the carrier mobility of GaSb films.

Keywords: PACS; 61.72. Tt; 73.20. Mf; 81.15. HiMolecular beam epitaxy; GaSb; Doping; Hall measurement

An ion momentum as a novel parameter for the preparation of the magnetostrictive thin film by Koji Makita; Mitsuaki Takeuchi; Masashi Sato; Hirohisa Uchida; Yoshihito Matsumura (pp. 1265-1267).

The Sm–Fe system known as Giant magnetostrictive (GM) thin films was prepared by d.c. magnetron sputtering process. The present study has shown the importance of the energetic incidence ions onto the depositing film surface for the magnetostrictive properties. The effect of ion bombardment on the magnetostrictive characteristics of GM films was quantitatively discussed. The new parameter, ion momentum, was proposed for the design of GM films.

Keywords: Giant magnetostriction; Thin film; Ion bombardment; Internal stress; Magnetostrictive susceptibility; Ion momentum; Sputtering process

Sections

Personal tools

Applied Surface Science (v.256, #4)

Sections

Personal tools

Local resources

Applied Surface Science (v.256, #4)