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Applied Surface Science (v.244, #1-4)

Author Index (pp. i-x).

Subject Index (pp. xi-xlix).

No Title by J. Temmyo; M. Tabe; Y. Nakanishi; Y. Fukuda (pp. 1-1).

Hydrogen and helium interactions in Si: phenomena obscure and not-so-obscure by S. Ashok (pp. 2-7).

The deliberate use of H- and He-related phenomena in crystalline Si (c-Si) has at times been hampered by concerns of the mobility of these light elements and hence potential device instability. However H is inevitably present in many Si processing steps, though not necessarily in the finished device. Accordingly one could differentiate between a transient or catalytic interaction of H with c-Si, and one where H resides permanently during device operation. We have uncovered phenomena on both domains, and these involve trapping and de-trapping of H by defective regions, thermal activation of latent defects in hydrogenated c-Si, and low-temperature activation of ion implanted dopant atoms. He differs from H principally by its electrical inactivity, but plays a significant role in altering the microstructure. The strong interaction of He with vacancy clusters results in nanocavities that act as excellent gettering sites and also enable localized minority carrier lifetime control. H and He thus offer possibilities for defect and impurity engineering in Si.

Keywords: PACS; 61.72.Ji; 61.72.Tt; 81.65.Rv; 71.55.Cn; 81.65.CfHydrogen in Si; Helium implantation; Defect engineering; Hydrogen-defect interactions; Dopant activation; Nanocavities

A new crystallization technique of Si films on glass substrate using thermal plasma jet by H. Kaku; S. Higashi; H. Taniguchi; H. Murakami; S. Miyazaki (pp. 8-11).

We have proposed a new crystallization technique of Si films on glass substrates using thermal plasma jet, and studied the crystallization of hydrogenated amorphous Si (a-Si:H) films as functions of the input power to the plasma source and the scanning speed of the substrate. Within the proper conditions of the input power and the scanning speed for the crystallization of Si films, higher input power and slower scanning speed lead to higher crystallinity. This technique enables as to crystallize Si films uniformly in the thickness even for the films as thick as ∼1μm.

Keywords: PACS; 52.77; 61.43; 81.05Thermal plasma jet; Crystallization; Polycrystalline Si; Thin-film transistor

Formation of microcrystalline germanium (μc-Ge:H) films from inductively coupled plasma CVD by Y. Okamoto; K. Makihara; S. Higashi; S. Miyazaki (pp. 12-15).

Inductively coupled RF plasma of H₂-diluted GeH₄ gas was applied to the growth of hydrogenated microcrystalline germanium (μc-Ge:H) films on quartz in a reactor with an external single-turn antenna placed on quartz plate window parallel to the substrate. The deposition rate, the crystallinity and the thickness of an amorphous incubation layer formed in the early stages of the film growth were evaluated as functions of GeH₄ concentration, gas flow rate, substrate temperature and the distance between the antenna and the grounded substrate susceptor. We demonstrated the growth of highly crystalized Ge films at a rate as high as 0.9nm/s at 250°C using a 8.3% GeH₄ diluted with H₂.

Keywords: PACS; 81.15.GhICP; μc-Ge; High-rate deposition; Crystallinity

Crystallization process of high-k gate dielectrics studied by surface X-ray diffraction by N. Terasawa; K. Akimoto; Y. Mizuno; A. Ichimiya; K. Sumitani; T. Takahashi; X.W. Zhang; H. Sugiyama; H. Kawata; T. Nabatame; A. Toriumi (pp. 16-20).

We have studied the crystallization process of HfO₂ and HfAlO_x films using grazing incidence X-ray diffraction (GIXRD) with synchrotron radiation. The HfO₂ and HfAlO_x films were grown by atomic layer deposition (ALD) on a chemical SiO₂ interfacial layer. X-ray diffraction (XRD) patterns of the HfO₂ film as-deposited contain not only the monoclinic phase but also the orthorhombic or tetragonal phase. With increasing annealing temperature, the orthorhombic or tetragonal phase decreases and disappears. The HfAlO_x film crystallized after annealing at 900�C. The crystallographic phase was the cubic phase of CaF₂ type.

Keywords: High-k; HfO; ₂; HfAlO; _x; ALD; Crystal structure

Influence of thickness of Hf buffer layer on the interfacial structures of sputtered HfO₂ on SiO₂/Si by Ruiqin Tan; Yasushi Azuma; Isao Kojima (pp. 21-25).

The influence of thickness of Hf–metal buffer layer on the interfacial diffusion and reaction was investigated using in situ X-ray photoelectron spectroscopy, scanning Auger microscope and grazing incident X-ray reflectivity. Hf–metal firstly reacted with native Si oxide forming Hf silicates, and all Si–O was further reduced to be Si⁰ after 1nm Hf–metal deposition. The Hf–metal and Hf-suboxide in Hf(1nm)/SiO₂/Si structure were further oxidized to be Hf⁴⁺ during HfO₂ sputtering deposition and post-deposition annealing. Si diffused out and reacted with HfO₂ during annealing. The Hf(1nm) buffer layer exhibited a better performance than the Hf(0.3nm) buffer layer in suppressing the diffusion of Si and the reaction between diffused Si and HfO₂.

Keywords: PACS; 77.55.+f; 81.15.Cd; 79.60.Jv; 82.80.Pv; 81.40.EHfO; ₂; Sputtering deposition; XPS; Annealing

Enhancement of donor ionization in phosphorus-doped n-diamond by Yasuo Koide (pp. 26-29).

In order to explore a possibility for controlling an electron concentration in phosphorus-doped n-diamond, electron and ionized-donor concentrations in n-diamond/cBN and n-diamond/AlN heterojunctions are analyzed by self-consistently solving Poisson and Schrödinger equations. Although the electron concentration is an order of 10¹¹cm⁻³ at room temperature for single n-diamond with a donor concentration of 5×10¹⁸cm⁻³ and a compensation ratio of 0.01, a modulation-doping technique predicts to provide full ionization of phosphorus donor in the n-diamond/cBN heterostructure and generation of an electron concentration larger than 10¹⁸cm⁻³ at room temperature.

Keywords: Diamond; cBN; AlN; n-Type; Phosphorus donor; Deep dopant; Superlattice doping; Ionization energy

Tight-binding quantum chemical molecular dynamics simulation of boron activation process in crystalline silicon by Tsuyoshi Masuda; Katsumi Sasata; Mohamed Elanany; Michihisa Koyama; Momoji Kubo; Akira Miyamoto (pp. 30-33).

The precise control of dopant atom is one of the most important challenges to fabricate ultra-shallow and highly doped junctions. In the present study, the activation process of B atom in Si crystal was investigated at low temperature of 500�C by using our tight-binding quantum chemical molecular dynamics method, which is over 5000 times faster than the conventional first-principles molecular dynamics method. The simulation results indicate that the B atom diffuses through the interstitial sites in the Si crystal even at low temperature of 500�C. Moreover, we found that the boron atom tends to migrate into the lattice vacancy and however the diffusion of the B atom is very hard after the boron atom is trapped in the single lattice vacancy. On the other hand, when there are two adjacent lattice vacancies in the Si crystal, the B atom migrates frequently between two adjacent vacancies back and forth. This result predicts that two adjacent lattice vacancies impede the B activation in the Si crystal. Finally, we confirmed that our tight-binding quantum chemical molecular dynamics program is very effective to elucidate the boron activation process in the Si crystal, considering the electronic states and electron transfer dynamics.

Keywords: PACS; 71.15.Pd; 85.40.-e; 85.40.RyBoron activation; Crystalline silicon; Tight-binding quantum chemical molecular dynamics; Lattice vacancy

Tight-binding quantum chemical molecular dynamics simulation of mechano-chemical reactions during chemical–mechanical polishing process of SiO₂ surface by CeO₂ particle by Arivazhagan Rajendran; Yasufumi Takahashi; Michihisa Koyama; Momoji Kubo; Akira Miyamoto (pp. 34-38).

Our tight-binding quantum chemical molecular dynamics method was applied to the investigations on the mechano-chemical reaction dynamics during the chemical–mechanical polishing (CMP) process of SiO₂ surface by CeO₂ particle. The mechanical forces introduced by the CeO₂ particle were found to accelerate the chemical reactions at the CeO₂–SiO₂ interface. The time profile of the bond population and atomic charges reveals the mechanism of the mechano-chemical reaction dynamics during the CMP process. The electronic states change from Ce⁴⁺ to Ce³⁺ was observed during the CMP process and this reduction reaction is related to the specific characteristics of the Ce element, which has two oxidation states, Ce³⁺ and Ce⁴⁺. Finally, we concluded that our tight-binding quantum chemical molecular dynamics method is an effective tool to clarify the mechano-chemical reaction dynamics during the CMP process, because these investigations cannot be realized by the conventional first-principles calculation and classical molecular dynamics method.

Keywords: PACS; 71.15.Pd; 73.61.Cw; 81.65.PsChemical–mechanical polishing; Tight-binding quantum chemical molecular dynamics; Mechano-chemical reaction

Influence of substrate dc bias on crystallinity of silicon films grown at a high rate from inductively-coupled plasma CVD by N. Kosku; H. Murakami; S. Higashi; S. Miyazaki (pp. 39-42).

We have investigated the effect of substrate bias on the microcrystalline film growth from inductively-coupled plasma (ICP) of H₂-diluted SiH₄ at 250°C to get an insight on the role of ion and electron incidence for the crystallization. By applying dc bias voltage to the substrate in the range of −20∼20V during the film growth, the crystallinity is improved significantly with no significant change in the deposition rate, but in contrast the application of biases as high as ±50V degrades the crystallinity. These results indicate that the incidence of ions or electrons with a moderate energy to the growing film surface promotes the nucleation and the growth of crystallites. Also, the optimum bias condition for the crystallization is changed with the antenna–substrate distance, which suggests the contribution of hydrogen radical flux to the crystalline film growth.

Keywords: PACS; 78.30.−j; 81.05.CyInductively-coupled plasma; Microcrystalline silicon; High rate deposition; Substrate bias

Thermal redistribution of hydrogen and boron in SiO₂ in SiN-capped p-type MOSFET structures by Yoshiya Kawashima; Satoka Aoyagi; Masahiro Kudo (pp. 43-46).

The thermal behavior of boron and hydrogen in a SiN-capped p-type MOSFET was investigated in order to explain SiN-enhanced boron diffusion in SiO₂. Measured hydrogen profiles indicated that hydrogen in the SiN migrated into the gate oxide during annealing under nitrogen. When this structure was annealed under nitrogen, the boron diffusivity in its SiO₂ increased to levels more than two orders of magnitude greater than that reported in SiO₂ annealed under hydrogen without a SiN cap. Nevertheless, the activation energy for boron diffusion in SiO₂ in a SiN-capped sample was the same as that for boron diffusion in SiO₂ annealed under hydrogen. This indicates that SiN-enhanced boron diffusion can be explained by the model proposed for hydrogen-induced boron diffusion: hydrogen termination of defects reduces the activation energy for interstitial-mediated diffusion of boron in SiO₂. Anomalous boron diffusion in SiO₂ in SiN-capped samples is thought to result from the SiN film facilitating the incorporation of a large amount of hydrogen in the SiO₂.

Keywords: PACS; 66.30.Jt; 61.72.SsBoron penetration; Diffusivity; Secondary ion mass spectrometry

Electrical and mechanical properties of surfactant-templated mesoporous silica thin films using Brij-76 surfactant by Sang-Bae Jung; Choo-Kyung Han; Hyung-Ho Park (pp. 47-50).

Ordered mesoporous silica films using Brij-76 surfactant were prepared from self-assembly of organic–inorganic species and their electrical/mechanical properties were investigated for low- k application. X-ray diffraction pattern revealed highly textured pore structure. Adequate dielectric properties could be realized by controlling the chemical species of silica wall. Porosity of mesoporous silica film was 39±2% and elastic modulus and hardness of the film were 14.4 and 1.25GPa, respectively. The dielectric constant and leakage current density were measured as 2.55 and less than 2×10⁻⁶A/cm² up to 1.6MV/cm, respectively.

Keywords: PACS; 85.40.LsLow-; k; Ordered; Mesoporous silica films; Brij-76; Surfactant

Evidence of refractive index change in glass substrates induced by high-density reactive ion plating deposition of SiO₂ films by Jan Mistrik; Ivan Ohlidal; Roman Antos; Mitsuru Aoyama; Tomuo Yamaguchi (pp. 51-54).

High-density reactive ion plating was used for SiO₂ coating of Schott B270 glass. Optical properties of the sample were intensively studied by spectroscopic ellipsometry, reflectance and transmittance. Several optical models accounting for different structural defects, i.e., (1) gradient profile of refractive index in SiO₂ layer, (2) transition layer between SiO₂ and glass, and (3) induced slow variation of glass refractive index close to SiO₂/glass interface were considered. The last one with increased value of substrate refractive index gave the best correspondence with the experimental data.

Keywords: PACS; 78.20.Ci; 81.40.TvEllipsometry; Reflectometry; Ion plating; SiO; ₂; /glass interface; Change of refractive index; Plasma-assisted deposition; Schott B270

Strain relaxation near high-k/Si interface by post-deposition annealing by T. Emoto; K. Akimoto; Y. Yoshida; A. Ichimiya; T. Nabatame; A. Toriumi (pp. 55-60).

We studied the effect of post-deposition annealing on a HfO₂/Si interface of by extremely asymmetric X-ray diffraction.Comparing the rocking curves before annealing the sample with those of the annealed sample, it is found that an interfacial layer with a density of 3g/cm³ grows at the interface between the HfO₂ layer and the substrate during post-deposition annealing. The wavelength dependency of the integrated intensities of the rocking curve for the as-deposited sample fluctuated with the observation position. This fluctuation was suppressed by annealing. From these results we concluded that the strain introduced into the substrate becomes homogeneous by annealing. Moreover, a quantitative estimation of the strain by curve fitting reveals the existence of compressive strain under the HfO₂ layer.

Keywords: High-k; HfO; ₂; Strain; Interfacial layer; Post-deposition anneal

Diffusion of Li in the silicon oxide films and evaluation of Li-induced surface potential by Masahiko Maeda; Teruyoshi Watanabe; Yasuhiro Imai; Yasuhiko Ishikawa; Michiharu Tabe (pp. 61-64).

The lithium doped and non-doped SiO₂ films were prepared by dip-coating method. Lithium atoms diffuse very fast in silicon oxide film and silicon substrate. As grown silicon nitride film prepared by plasma-enhanced chemical vapor deposition (PECVD) is insufficient as barrier layer for lithium diffusion. Lithium atoms can keep in the silicon oxide film by using the silicon nitride films densified by high temperature heat treatment. Surface potential of the insulating films involved alkaline metal atoms can be measured by Kelvin probe force microscope (KFM). Although the data have considerable scatterings, the surface potential of the lithium doped films was showed to be relatively positive. It is also found that the hydrogen atoms incorporated in the silicon nitride films used as diffusion barrier layer have a large influence on the surface potential. The possibility of KFM is confirmed for estimation of the surface potential of the insulating films with charged atoms.

Keywords: PACS; 81.20.Fw; 81.70.JbSol–gel; Li diffusion; KFM; Surface potential

Surface elemental segregation and the Stranski–Krastanow epitaxial islanding transition by A.G. Cullis; D.J. Norris; M.A. Migliorato; M. Hopkinson (pp. 65-70).

It is shown that a new segregation-based mechanism underpins the Stranski–Krastanow (S–K) epitaxial islanding transition in both the In_xGa1−_xAs/GaAs and Si1−_xGe_x/Si systems over wide ranges of growth conditions. Quantitative segregation calculations allow critical ‘wetting’ layer thicknesses to be derived and, for the In_xGa1−_xAs/GaAs system ( x=0.25–1), such calculations show good agreement with experimental measurements. The segregation-mediated driving force is considered to be important, also, for all other epitaxial systems which comprise chemically similar but substantially misfitting materials and which exhibit the S–K transition.

Keywords: Epitaxy; Stranski–Krastanow transition; Islanding transition; Quantum dot

Surface-related reduction of photoluminescence in GaAs quantum wires and its recovery by new passivation by Nanako Shiozaki; Sanguan Anantathanasarn; Taketomo Sato; Tamotsu Hashizume; Hideki Hasegawa (pp. 71-74).

Etched GaAs quantum wires (QWRs) and selectively grown (SG) QWRs were fabricated, and dependence of their photoluminescence (PL) properties on QWR width ( W) and QWR distance to surface ( d) were investigated. PL intensity greatly reduced with reduction of W and d, due to non-radiative recombination through surface states. Surface passivation by growing a Si interface control layer (Si-ICL) on group III-terminated surfaces greatly improved PL properties.

Keywords: GaAs; AlGaAs; Quantum wire; Surface passivation; Surface states; Photoluminescence

Control of the nucleation density of Si quantum dots by remote hydrogen plasma treatment by K. Makihara; H. Deki; H. Murakami; S. Higashi; S. Miyazaki (pp. 75-78).

The influence of surface pretreatments by remote hydrogen and/or argon plasma on the silicon nucleation density on thermally grown SiO₂ in the early stages of low pressure chemical vapor deposition (LPCVD) using monosilane (SiH₄) has been studied to control the areal density of Si quantum dots (Si-QDs) on SiO₂. In the remote H₂ (or D₂) plasma treatments prior to SiH₄-LPCVD, the formation of SiOH (SiOD) surface bonds, which act as reactive sites, was confirmed from no changes in the SiO₂ surface microroughness and in the thickness. In fact, by a H₂ plasma pretreatment, the areal density of Si-QDs as high as 7×10¹⁰cm⁻² was obtained in the LPCVD condition of the dot density with as low as 6×10⁸cm⁻² on as-grown SiO₂. By changing the pressure and the substrate temperature in the H₂ plasma pretreatment, the dot density was controlled in the range of 4×10⁹ to 7×10¹⁰cm⁻². Further increase in the dot density and improvement of the dot size uniformity was also demonstrated by the pretreatment of Ar plasma followed by H₂ plasma, presumably because of improved uniformity and integrity in SiO₂ surface coverage with OH bonds just before LPCVD.

Keywords: PACS; 61. 46.+wSi quantum dots; Plasma treatment; LPCVD

Optical effects in silica glass during implantation of 60keV Cu⁻ ions by O.A. Plaksin; Y. Takeda; K. Kono; H. Amekura; N. Umeda; N. Kishimoto (pp. 79-83).

Spectra of the optical transmission and ion-induced photon emission (IIPE) of silica glass were measured during implantation of 60keV Cu⁻ ions at ion fluxes from 1 to 75μA/cm² up to a fluence of 2×10¹⁷ions/cm², aimed at monitoring the formation of Cu nanoparticles. The precipitation threshold of Cu atoms is flux-dependent. At fluxes from 1 to 10μA/cm², the formation of nanoparticles is efficient up to fluences of 2×10¹⁷ions/cm². The efficiency of IIPE of Cu⁺ solutes in silica glass (band at 2.25eV) is proportional to a total concentration of Cu solutes. In a single-phase region (solid solution of Cu atoms), the efficiency of IIPE of Cu⁺ solutes is flux-independent. In a two-phase region (solid solution and Cu nanoparticles), the dynamic balance between the nanoparticles and Cu solutes determines the flux-dependent behavior of the efficiency of IIPE.

Keywords: PACS; 61.46.+w; 78.67.−n; 81.07.Bc; 81.16.−cHeavy-ion implantation; Metal nanoparticles; Silica glass; In situ optical transmission; Ion-induced photon emission

Study on ECR dry etching and selective MBE growth of AlGaN/GaN for fabrication of quantum nanostructures on GaN (0001) substrates by Takeshi Oikawa; Fumitaro Ishikawa; Taketomo Sato; Tamotsu Hashizume; Hideki Hasegawa (pp. 84-87).

This paper attempts to form AlGaN/GaN quantum wire (QWR) network structures on patterned GaN (0001) substrates by selective molecular beam epitaxy (MBE) growth. Substrate patterns were prepared along〈112¯0〉- and〈11¯00〉-directions by electron cyclotron resonance assisted reactive-ion beam etching (ECR-RIBE) process. Selective growth was possible for both directions in the case of GaN growth, but only in the〈112¯0〉-direction in the case of AlGaN growth. A hexagonal QWR network was successfully grown on a hexagonal mesa pattern by combining the〈112¯0〉-direction and two other equivalent directions. AFM observation confirmed excellent surface morphology of the grown network. A clear cathodoluminescence (CL) peak coming from the embedded AlGaN/GaN QWR structure was clearly identified.

Keywords: PACS; 81.07.Vb; 81.16.Dn; 78.67.DeGaN; AlGaN; Quantum wire; Selective MBE growth; Dry etching

Control of photoluminescence wavelength from uniform InAs quantum dots by annealing by Yoshiyuki Kobayashi; Koichi Yamaguchi (pp. 88-91).

Post-growth annealing of uniform InAs quantum dots (QDs) grown on GaAs(001) substrates was investigated, and obtained results gave some useful information about control of QD energy level and an intermixing effect between In and Ga atoms. In particular, a wide control of photoluminescence (PL) peak energy (312meV) and an extremely narrow PL linewidth (13meV) were obtained from uniform QDs annealed at 700�C. Photoluminescence properties of annealed QDs depending on anneal conditions were explained by modification of the QD structure and, an interdiffussion effect was discussed.

Keywords: PACS; 61.72.c; 66.30.Ny; 73.20.Dx; 78.55.–m; 78.55.Et; 81.15.HiInAs; Quantum dot; Photoluminescence; Molecular beam epitaxy; GaAs; Interdiffusion; Post-growth annealing

Changes in the electronic energy structure of CdSe nanocrystals of close-packed array by in situ anneal by Hyun-Ju Choi; Jun-Kyu Yang; Sook Yoon; Hyung-Ho Park (pp. 92-95).

We synthesized colloidal CdSe nanocrystals through solution process. Nanocrystals showed quantum confinement effects well in solution form. The CdSe nanocrystals coated on Si(100) wafers were vacuum annealed and analyzed in situ using X-ray absorption and photoelectron spectroscopy to investigate the electronic energy structure of CdSe nanocrystals. As nanocrystalline solids were annealed at high temperature, the absorption edge of Cd M level and valence band maximum of CdSe decreased as the core level binding energy of Cd 3d. In addition, a red shift with the increase of annealing temperature was also confirmed by the photoluminescence observation of CdSe nanocrystals on glass substrate.

Keywords: PACS; 71.24Nanocrystals; CdSe; Electronic structure

Growth of ZnS nanocombs with ZnO sheath by thermal evaporation by M.Y. Lu; P.Y. Su; Y.L. Chueh; L.J. Chen; L.J. Chou (pp. 96-100).

Self-assembled zinc sulfide (ZnS) of wurtzite structure nanocombs with a ZnO sheath have been grown using a simple catalyst-free thermal evaporation technique in the alumina furnace. The ZnS nanocombs are as long as to several tens of micrometers. The teeth with ZnO sheath are about 200nm in length and 30nm in width. The ZnO sheath is likely formed at cool-down stage due to the residual O₂.

Keywords: PACS; 73.22.−f; 68.37.Hk; 68.37.Lp; 68.60.WmZnS; Nanocomb; ZnO sheath

Growth of In₂O₃ nanocrystal chains by a vapor transport and condensation method by C.L. Hsin; J.H. He; L.J. Chen (pp. 101-106).

Self-assembled In₂O₃ nanocrystal chains have been synthesized by a vapor transport and condensation method. The nanocrystal chains were straight and with diameters of 100–200nm. The nanocrystal and nanowire were found to be of the same orientation. The pyramid and triangular slab-like nanostructures were also found and discussed. The possible formation mechanism of these nanostructures is discussed.

Keywords: PACS; 73.22−f; 68.37.Hk; 68.37.Lp; 68.60.WmIndium oxide; Nanowires; Nanocrystal chains

Nano-scale Cu metal patterning by using an atomic force microscope by Y. Tomita; Y. Hasegawa; K. Kobayashi (pp. 107-110).

Nano-scale Cu metal patterning was achieved by the use of an atomic force microscope. When the scanning with the cantilever of atomic force microscope (AFM) covered with the solid electrolyte was carried at a negative voltage, the Cu metal was deposited on TiO₂ substrates. The Cu metal on TiO₂, a glass and Si substrates was absorbed at the positive voltage. The deposition and the absorption of Cu could be repeated and carried out at room temperature without a specific treatment. The letters “Y�? and “T�? were written with 50nm resolution by the scanning. The reaction between the tip of the cantilever and substrate is a simple electrochemical reaction.

Keywords: PACS; 07.79.LhAtomic force microscope; Ionic conductor; Metal patterning; Nano-fabrication

Characterization of amorphous carbon film-coated nanotubes as electron field emission material by M. Nagatsu; T. Yoshida; S. Kurita; K. Murakami (pp. 111-114).

Effects of amorphous carbon (a-C) thin film coating over carbon nanotubes (CNTs) on the field emission characteristics have been studied. Large-area surface-wave plasma (SWP) device was used both for growth of multi-wall CNTs on Ni-evaporated Si substrate and for deposition of a-C thin layer over CNTs. Field emission characteristics of the a-C film-coated CNTs prepared with different CVD durations were investigated. Experimental results show that the emission performance was significantly improved by coating a-C film typically with a thickness of 0.6–1μm, that is, the ignition voltage for electron emission was reduced from 240V for the sample of CNTs only to 110V for that of CNTs deposited with a-C film during 60min. The surface morphology has been also studied using the field emission type scanning electron microscopy (FE-SEM). It was deduced that the reduction of ignition voltage was due to the field enhancement originated from grain shape structures of the surface after a-C film deposition.

Keywords: PACS; 81.07.De; 79.70.+q; 52.77.DqField emission; Nanotube; Plasma CVD; Microwave plasma

Vacancy ordering in self-assembled erbium silicide nanowires on atomically clean Si(001) by W.C. Tsai; H.C. Hsu; H.F. Hsu; L.J. Chen (pp. 115-119).

ErSi2−_x nanowires (NWs) were grown on Si(001). The orientation relationships between ErSi2−_x and Si(001) were determined to be ErSi2−_x[0001]//Si[11¯0], ErSi2−_x(11¯00)//Si(001) and ErSi2−_x[112¯0]//Si[110], ErSi2−_x(11¯00)//Si(001). Due to the anisotropy of lattice matches on Si(001), ErSi2−_x has a preferred direction of growth. Since Si is expected to be the dominant diffusing species during intermixing, the observation of NWs surrounded by recessed silicon steps is attributed to the release of Si atoms causing retreat of the steps. Owing to the difference in growth shape and Er deposition rate, the vacancy ordering structure along c-axis is more ordered in NWs than in thin-film system. The analysis indicates that the variation of vacancy ordering structures depends on the strain relaxation on the surface.

Keywords: PACS; 68.37.−d; 68.37.Ef; 68.37.Lp; 73.22.−fNanowires; Rare earth; Silicide; Epitaxy; Self-assembled; Defects

2D lattice formation by YAG:Nd laser on the surface of Ge single crystal by A. Medvid; Y. Fukuda; A. Michko; P. Onufrievs; Y. Anma (pp. 120-123).

Experimentally observed self-organization of a 2D lattice on the surface of Ge single crystal after irradiation by pulsed YAG:Nd laser is reported. The 2D lattice consists of nano-size elevations arranged in a pattern of C6_i point group symmetry and is characterized by translational symmetry with the period of 1μm. Calculations of time depended distribution of temperature in the bulk of the Ge sample are presented to explain the phenomenon. The calculations show that overheating of the crystal lattice occurs at laser radiation intensities exceeding 30MW/cm². According to synergetic ideas, the presence of the non-equilibrium liquid phase of Ge and huge gradient of temperature (∼3×10⁸K/m) can lead to self-organization of the 2D lattice similar to Bernar's cells.

Keywords: PACS; 42.62.−b; 71.55.Cn; 73.63.BdSelf-organization; 2D lattice; YAG:Nd laser; Ge single crystal

Carbon nanotube adsorbed on hydrogenated Si(001) surfaces by R.H. Miwa; W. Orellana; A. Fazzio (pp. 124-128).

The structural and electronic properties of a metallic single-walled carbon nanotube (CNT), adsorbed on hydrogenated Si(001) surfaces, have been investigated by first-principles calculations. We find that the electronic properties of the adsorbed CNT can be ruled by the H concentration along the CNT–H/Si(001) contact region. (i) On the fully hydrogenated Si(001), the CNT is physisorbed, preserving almost unchanged its metallic character. (ii) Removing half the H atoms along the adsorption site, we find an enhancement on the metallicity of the adsorbed CNT. (iii) When all the H atoms along the adsorption site are removed, the adsorbed CNT becomes semiconducting, exhibiting an energy gap. These results suggest that metallic CNTs adsorbed on H/Si(001) could be transformed into metal–semiconductor junctions by grading the H concentration along the CNT–surface interface.

Keywords: Carbon nanotube; Silicon surface; Ab-initio calculations

Atomic-scale theoretical investigations of compound semiconductor surfaces by G.P. Srivastava (pp. 129-136).

Atomic-scale theoretical investigations of clean and covered low-index surfaces of compound semiconductors are presented. Particular emphasis is laid on the role of the electron counting rule (ECR) in governing plausible surface reconstructions. Trends are presented for the characeristic tilt of the topmost atomic layer and the highest localised phonon mode on nonpolar III–V(110) surfaces, including III-nitride compounds. Reconstructions and electronic properties of polar surfaces are explained in terms of dimer formation on (001), and trimer and/or chain formation on (111) faces. It is pointed out that some surface reconstructions stabilise as a result of a balance between the ECR and minimization of adsorbate-induced local distortion. This is demonstrated for the long-range ordered reconstruction on the Sb:GaAs(111)B surface.

Keywords: PACS; 68.35; 71.15; 73.20Surfaces; Surface reconstructions; Surface electrons; Surface phonons; Compound semiconductors; Density functional theory; Pseudopotential method

Sb adsorption onto In nanocluster array structure formed on a Si(111)–(7×7) by M. Saito; C. Takeuchi; M. Mori; T. Tambo; C. Tatsuyama (pp. 137-140).

The application of self organized growth method (magic clustering method) for the formation of new type of nanocluster is reported. Sb has been deposited onto bare Si(111)–(7×7) reconstruction and onto In magic nanocluster array structure. And Sb interaction with substrate and atomic structural change have been studied using scanning tunneling microscopy. Furthermore, in the latter case of Sb adsorption, the cluster with new components was observed. This new type cluster is obtained by using magic clustering method and the tendency of Sb atoms substitution for In atoms.

Keywords: PACS; 61.46.+w; 07.79.CzIndium; Antimony; Silicon; Self-assembly; Scanning tunneling microscopy

Inclined N₂ desorption in N₂O decomposition on Rh(110) by T. Matsushima; K. Imamura; H. Horino; A. Hiratsuka; Y.-S. Ma; I.I. Rzeznicka; O. Nakagoe (pp. 141-144).

The angular distribution of desorbing N₂ was studied in transient N₂O decomposition on Rh(110) by both pressure jump and temperature-programmed decomposition (TPD). Even at 60K, N₂O was decomposed, emitting N₂ along either around 68° or 30° off normal towards the [001] direction. In the latter TPD, N₂ desorption yielded five peaks in the range of 70–160K. Four of them involved desorption in similarly inclined ways.

Keywords: PACS; 82.65.JvNitrous oxide; Nitrogen; Decomposition; Rhodium; Angular distribution

Reflection high-energy positron diffraction study of a Si(001) surface by K. Hayashi; Y. Fukaya; A. Kawasuso; A. Ichimiya (pp. 145-148).

We have studied the positron diffraction from the Si(001) 2�1 surfaces. In the diffraction patterns the fractional order spots are brightly visible. The vertical positions of the dimer are determined from the numerical analysis of the rocking curves based on the dynamical diffraction theory at room temperature and 130K. The heights of the two atoms of the dimer are both 1.3�0.2� at room temperature and 1.3�0.2� and 1.1�0.2� at 130K from the layer below the dimers.

Keywords: PACS; 61.14.−x; 68.35.BsReflection high-energy positron diffraction; Total reflection; Si(0; 0; 1); Rocking curve; Dynamical calculation; Diffraction pattern

Positron diffraction study of SiC(0001) surface by A. Kawasuso; M. Maekawa; M. Yoshikawa; A. Ichimiya (pp. 149-152).

Surface structures of 6H SiC(0001) after heat treatment in a UHV has been studied using reflection high-energy positron diffraction (RHEPD). After heat treatment at 900°C, a typical interference effect of positron waves due to Si adatoms appears in the total reflection region of the rocking curve. The further heat treatment at 1100°C results in surface graphitization. The rocking curve is well reproduced by theoretical calculation assuming the graphite monolayer on SiC substrate. The interlayer distance is fairly large (2.5–3.2Å), which is comparable to that in the graphite monocrystal suggesting that the weak binding of the graphite monolayer to the SiC surface by the van der Waals force.

Keywords: PACS; 61.14.Hg; 68.35.Bs; 68.47.Fg; 68.49.−hReflection high-energy positron diffraction; RHEPD; SiC(0; 0; 0; 1); Total reflection

Surface structure and electronic states of sulfur-treated InP(111)A studied by LEED, AES, STM, and IPES by M. Shimomura; Y. Sano; N. Sanada; L.L. Cao; Y. Fukuda (pp. 153-156).

The structure and electronic states of an (NH₄)₂S_x-treated InP(111)A surface has been studied by using low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), scanning tunneling microscopy (STM), and inverse photoemission spectroscopy (IPES). The sample annealed in ultra-high vacuum (UHV) condition at ∼300–400°C showed a 2×2-LEED pattern. Oval-shaped protrusions are observed in filled-state STM images. IPES intensity of the (2×2)-S surface at E_F +1–3eV and +4–6eV is decreased by the (NH₄)₂S_x treatment. Based on these results, a plausible structural model is discussed.

Keywords: PACS; 68.35.−p; 68.35.Bs; 73.20.−r; 73.20.AtAuger electron spectroscopy; Low-energy electron diffraction; Scanning tunneling microscopy; Inverse photoemission spectroscopy; Surface relaxation and reconstruction; Indium phosphide

The geometry of Bi nanolines on Si(001) by R.H. Miwa; J.M. MacLeod; G.P. Srivastava; A.B. McLean (pp. 157-160).

A study of the Bi nanoline geometry on Si(001) has been performed using a combination of ab initio theoretical technique and scanning tunnelling microscopy (STM). Our calculations demonstrate decisively that the recently proposed Haiku geometry is a lower energy configuration than any of the previously proposed line geometries. Furthermore, we have made comparisons between STM constant-current topographs of the lines and Tersoff–Haman STM simulations. Although the Haiku and the Miki geometries both reproduce the main features of the constant-current topographs, the simulated STM images of the Miki geometry have a dark stripe between the dimer rows that does not correspond well with experiment.

Keywords: PACS; 73.20.−r; 73.20.At; 73.21.HbSilicon surface; Ab initio calculations; Nanolines; Scanning tunnelling microscopy; Semiconductor hetero-epitaxy

STM observation of Bi line structures on the Si(100) surface with Ag deposition by T. Itoh; S. Kashirajima; M. Naitoh; S. Nishigaki; F. Shoji (pp. 161-165).

We report a dynamic formation process of Bi line structures (BLS) and their reaction dynamics with foreign atoms on Si(100) surfaces by scanning tunneling microscopy (STM). BLSs consisting of Bi dimers are formed on the Si(100) surface after bismuth deposition at 400–500°C. From consecutive STM images taken after Bi deposition on the surface, we found that BLSs are easily formed when the terraces at the front of the BLS growth contains surface defects. When Ag atoms were deposited on the Si(100) surface containing the BLSs, we found that Ag atoms are preferentially adsorbed on the Si terraces rather than on BLSs.

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

Observation of Si(111)-3�3-Ag surface at room temperature by reflection high-energy positron diffraction by Y. Fukaya; A. Kawasuso; K. Hayashi; A. Ichimiya (pp. 166-169).

We have observed the Si(111)-3�3-Ag surface using reflection high-energy positron diffraction (RHEPD). The RHEPD pattern clearly displays the intense (�2/3�2/3) spots, which results from the large magnitude of the scattering factor for the Ag atoms. The rocking curves of the RHPED at room temperature have been measured and analyzed by means of the dynamical diffraction theory. We found that the atomic height of the topmost Ag triangle is 0.77� and is well in accordance with those determined by the other methods.

Keywords: PACS; 68.35.Bs; 61.14.HgSurface structure; Reflection high-energy positron diffraction (RHEPD); Total reflection; Silicon; Silver

An empirical potential approach to structural stability of GaN_xAs1−_x thin films on GaAs(111) by Tomonori Ito; Takashi Suda; Toru Akiyama; Kohji Nakamura (pp. 170-173).

Structural stability of GaN_xAs1−_x thin films coherently grown on GaAs(111) is systematically investigated based on an empirical potential, which incorporates electrostatic energies due to bond charges and ionic charges. Using the empirical potential, the system energies of zinc blende (ZB) and wurtzite (W) structured GaN_xAs1−_x thin films are calculated over the entire concentration range. The calculated results predict that the structural phase transition from ZB to W occurs at x_c∼0.5, which differs from x_c∼0.7 expected by the electrostatic energy contribution dominating W–ZB polytypism in end members such as GaN and GaAs. The difference between the values of x_c is clarified in terms of difference in bond lengths distribution in ZB-GaN_xAs1−_x and W-GaN_xAs1−_x. Further calculations for interface structures between ZB- or W-GaN_xAs1−_x thin films and GaAs(111) substrate reveal that ZB-type stacking sequence is more favorable than W-type stacking sequence at the interface. Consequently, ZB-GaN_xAs1−_x thin films can be fabricated in the concentration range of x<0.5 on the GaAs(111), whereas W-GaN_xAs1−_x thin films are formed with ZB-type stacking interface in the concentration range of x≥0.5.

Keywords: PACS; 61.50.Ks; 64.70.Kb; 68.35.Ct; 68.55.NqGaN; _x; As; 1−; _x; Computer simulation; Structural phase transition; Thin films

Photoemission spectroscopy study of the oxidation of HfC(100) by K. Edamoto; Y. Shirotori; T. Sato; K. Ozawa (pp. 174-177).

The oxidation process of an HfC(100) surface has been investigated using photoemission spectroscopy utilizing synchrotron radiation. It is found that, when the HfC(100) surface is exposed to O₂ at room temperature, the C atoms of the surface region react with oxygen to form CO molecules and are desorbed from the substrate. The Hf atoms of the surface region are oxidized by stepwise reactions, and are finally oxidized to form an HfO₂-like layer at high coverages (>10L).

Keywords: PACS; 73.20.−r; 79.60.DpPhotoelectron spectroscopy; Adsorption; Oxidation; HfC

An ab initio-based approach to Ga adatom migration on GaAs( n11)A–(001) non-planar surfaces by Tomonori Ito; Koichi Asano; Toru Akiyama; Kohji Nakamura; Kenji Shiraishi; Akihito Taguchi (pp. 178-181).

The behavior of Ga adatoms on GaAs( n11)A ( n=2, 3, 4), (001)-(2×4)β2 and non-planar surfaces consisting of the (211)A and (001) are systematically investigated by ab initio-based approach and the Monte Carlo (MC) method. The ab initio total energy calculations clarify strong dependence of Ga adsorption energies on the surface index. Comparing these adsorption energies of Ga with the Ga chemical potentials in the vapor phase, Ga atoms predominantly adsorb on the (211)A and (311)A surfaces at high temperatures even beyond ∼1100K. On the other hand, Ga atoms tend to desorb from the (411)A and (001) surfaces at the high temperatures. Furthermore, the MC simulations reveal that diffusion coefficient of Ga adatoms across the (001) surface is larger than that on the (211)A surface. This is because Ga migration potential energies on the (001) surface are smaller than those on the (211)A surface. Reflecting these results, Ga adatoms on the (211)A–(001) non-planar surface migrate on the (211)A side surface beyond ∼1100K, whereas Ga adatoms mainly diffuse across the (001) surface below ∼1100K.

Keywords: PACS; 68.43.Bc; 68.43.Jk; 68.43.Mn; 68.47.FgGaAs; Computer simulation; Adsorption; Migration; Molecular beam epitaxy

An empirical potential approach to dislocation formation and structural stability in GaN_xAs1−_x by Keiichi Kawamoto; Takashi Suda; Toru Akiyama; Kohji Nakamura; Tomonori Ito (pp. 182-185).

We study the feasibility of our empirical potential to dislocation formation and its contribution to structural stability in GaN_xAs1−_x. The feasibility is exemplified by the calculations of the dislocation core energy and core radius for various dislocation core structures in wurtzite structured GaN. Moreover, we carry out theoretical analyses of the structural stability for GaN_xAs1−_x with dislocation whose core structure is described by five- and seven-coordinated channels (5/7 core) over the entire concentration range. The GaN_xAs1−_x changes its structure from zinc blende to wurtzite at the concentration for phase transition x_c=0.3 with dislocation and x_c=0.4 without dislocation. This is because the 5/7 core favors the wurtzite structured GaN_xAs1−_x with lower core energy than that in zinc blende structured GaN_xAs1−_x.

Keywords: PACS; 61.72.Bb; 81.10.Aj; 64.70.KbGaN; _x; As; 1−; _x; Dislocation; Structural stability; Electrostatic energy

Theoretical investigation of phase transition on GaAs(001)-c(4�4) surface by Hirotoshi Ishizaki; Toru Akiyama; Kohji Nakamura; Kenji Shiraishi; Akihito Taguchi; Tomonori Ito (pp. 186-189).

The surface phase transition between GaAs(001)-c(4×4) and -(2×4)β2 surfaces is systematically investigated by using our ab initio-based approach. The phase diagram calculations for the c(4×4) surfaces as functions of temperature and As pressure reveal that three kinds of c(4×4) surfaces consisting of Ga–As dimers and/or Ga–Ga dimers become stable near the phase transition temperature. The electron counting Monte Carlo simulation and ab initio calculations are also performed to investigate the structural change of the c(4×4) surface after predepositing a 0.5 monolayer of Ga on the three kinds of c(4×4) surfaces. The calculated results suggest that the c(4×4) surfaces consisting of three Ga–As dimers or one Ga–Ga dimer and two Ga–As dimers in the (4×4) surface unit cell possibly change their structures to (2×4)β2 structures with Ga–As surface dimers. The conventional (2×4)β2 surface consisting of As dimers finally appears due to destabilization of Ga–As dimers at high temperature and high pressure.

Keywords: PACS; 68.35.Bs; 68.43.Bc; 81.05.EaGaAs surfaces; Surface phase transition; Electron counting Monte Carlo simulation; Ab initio calculations

Theoretical study on hydrogen reaction processes on H/Si(001) surface by N. Takahashi; J. Nara; T. Uda; Y. Nakamura; Y. Tateyama; T. Ohno (pp. 190-194).

The reaction processes of an incident H atom with the H- or D-terminated Si(001)-(2�1) surface are theoretically investigated by using first-principles molecular dynamics simulations. Because the atomic hydrogen reaction process producing an H₂ (HD) molecule is exothermic, this reaction is considered to be observed in many cases. It is found that an H₂ (HD) molecule is produced in all of the cases treated in this study. The final kinetic energy of the resultant H₂ (HD) molecule is found to be mostly distributed to the vibrational energy, whereas the translational energy of the resultant molecule is estimated to be relatively low. In this reaction process, a resultant H₂ (HD) molecule is weakly trapped into a bound state site between two Si dimer rows on the surface followed by the desorption from the surface. This type of reaction processes corresponds to the direct abstraction of Eley-Rideal mechanism, which is in good agreement with the previous experimental results.

Keywords: PACS; 68.35.Ja; 68.43.Mn; 68.43.PqSi surface reaction; Atomic hydrogen; Hydrogen termination; First-principles calculation; Exothermicity; Energy distribution

Theoretical study on the electronic and molecular properties of ground and excited states of ethylenedioxythiophene and styrenesulphonic acid by Govindasamy Agalya; Chen Lv; Xiaojing Wang; Michihisa Koyama; Momoji Kubo; Akira Miyamoto (pp. 195-198).

Poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(4-styrenesulphonate) (PSS) has been widely used in light-emitting devices as hole transport layer and in photovoltaic devices as hole-collecting layer. In the present study, various quantum chemical calculations were carried out for the investigation of low-lying excited states of ethylenedioxythiophene (EDOT), and styrenesulphonic acid. The lowest adiabatic transition energies were calculated using configuration interaction singles method. The time-dependent density functional theory was also applied for the calculation of the vertical excitation energies. Differential self-consistent-field-based density functional theory method is well known to show good performance for the geometry of excited state and hence it was also applied to study of the first singlet excited state. In addition to the calculation of the monomer, the electronic properties of PEDOT were calculated by periodic density functional theory method and the result is in good agreement with the experimental observation.

Keywords: PACS; 31.70.Hq; 71.15.Pd; 82.35.Cd; 82.50.HpConducting polymer; Excited state; Transition energy; Configuration interaction singles; Time-dependent density functional theory; Differential self-consistent-field-based density functional theory; Periodic density functional theory

Measurements of critical micelle concentration (CMC) using optical fiber covered with porous sol–gel cladding by H. Isobe; C.D. Singh; H. Katsumata; H. Suzuki; T. Fujinami; M. Ogita (pp. 199-202).

We present a sol–gel derived coating optical fiber sensors for measurement of critical micelle concentration of surfactants. A sol–gel process for making porous silica and coat the fiber core with sensing material is described. CMC detection is based on an adsorption effect in sample solution mainly of sodium dodecylbenzenesulfonate. Three different particles size of sol–gel porous cladding were tested. Test results show that the sensitivity of the small particle size porous sol–gel cladding optical fiber is higher than that of large particle size sol–gel cladding one. It was also found that measurement of CMC point using this method is very accurate and cost effective.

Keywords: PACS; 42.81 −IOptical fiber; Surfactants; Adsorption effect; Sol–Gel

Formation of pores in Ge single crystal by laser radiation by A. Medvid’; A. Mychko; A. Krivich; P. Onufrijevs (pp. 203-208).

Formation of a porous structure on the surface of Ge single crystals by pulsed YAG:Nd laser irradiation at the intensity of ∼25MW/cm² is reported. An increase of surface recombination velocity on the irradiated surface by a factor of 100 is observed and explained by increase of the geometric area of the surface due to formation of pores. The latter is attributed to inhomogeneous pressure of a pulsed laser beam on the melting irradiated surface of the crystal.

Keywords: PACS; 42.62.−b; 71.55.Cn; 73.63.BdPores; Ge single crystal; Laser radiation; Magnetoconcentration effect; AFM

Obliquely deposited metal films for polarizers by Yasuhiko Takeda; Norihito Takeuchi; Tatsuo Fukano; Tomoyoshi Motohiro (pp. 209-212).

The performance of obliquely deposited metal films as polarizers, which can be used for normally incident light, was improved. The relation between microscopic columnar structures and dichroism of the films was investigated by depositing various kinds of metals with changing deposition angles. The influence of substrate materials was also examined. It was revealed that enlargement of the spacing between the neighboring columns is the most significant to attain a good extinction ratio and a low insertion loss. For the best performance, transmittances for p-polarization and s-polarization of 50% and 1%, respectively, at a wavelength of 681nm were attained by depositing Al on poly(methyl-methacrylate) substrates at a deposition angle of 87�.

Keywords: PACS; 78.66.Bz; 68.55.Jk; 81.15.EfOblique deposition; Dichroism; Polarizer

Modelling of columnar growth in continuum ballistic deposition by Yoshihisa Enomoto; Masaharu Taguchi (pp. 213-216).

The dynamics of morphological change of the growing film surface during a vertical ballistic deposition is numerically studied by means of a phenomenological model. The model is a phenomenological continuum model, described by a pair of coupled equations of the phase field for a growing film and the density field for ballistic deposited particles. Several computer simulations show that morphological transitions of the growing surface occur on varying phenomenological parameters of the model. Especially, it is found that stable columnar structures are obtained within some ranges of parameters.

Keywords: PACS; 81.10.Aj; 81.15.Aa; 82.20.XrColumnar structure; Ballistic deposition; Thin film; Phase field model

Preparation and characterization of Rhodamine B and Alq₃ thin films deposited by solution jet beam method by Y. Okabayashi; T. Mitarai; S. Yamazaki; R. Matsuyama; K. Kanai; Y. Ouchi; K. Seki (pp. 217-220).

We report the solution jet beam method as a novel technique to fabricate organic thin films in vacuum. The method can be applied even to ionic organic materials, which cannot be vacuum evaporated due to thermal decomposition. Thin films of RhB (Rhodamine B) and Alq₃ (tris(8-hydroxyquinoline)aluminum) were fabricated and characterized. Organic light emitting diodes (OLEDs) were also fabricated using Alq₃ films prepared by this method.

Keywords: PACS; 81.15.Ef; 81.15.RsOrganic thin film; Jet; Spray; Alq; ₃; Rhodamine B

Spectroscopic ellipsometry on sinusoidal surface-relief gratings by R. Antos; I. Ohlidal; D. Franta; P. Klapetek; J. Mistrik; T. Yamaguchi; S. Visnovsky (pp. 221-224).

Spectroscopic ellipsometry (SE) is used to study a sinusoidal-relief grating fabricated on a surface of transparent polymer. An optically thick polymer layer is situated on a glass substrate and its refraction index is optically matched to the index of the glass. The rigorous coupled-wave analysis, implemented as the airy-like internal reflection series, is applied to calculate the optical response of the relief grating. The entire optical response of the sample is determined by employing incoherent backreflections at the interface between the polymer and the glass. The parameters describing the dimensions and the real shape of the sine-like relief, as well as the quality of the optical matching between the polymer and the glass, are determined using SE together with atomic force microscopy as a complementary technique.

Keywords: PACS; 06.20.Dk; 42.25.Fx; 42.70.Ce; 42.70.Jk; 42.79.Dj; 42.82.BqOptical metrology; Spectroscopic ellipsometry; Sinusoidal grating; Wood anomaly; RCWA; Incoherent light

Spectroscopic ellipsometry on lamellar gratings by R. Antos; I. Ohlidal; J. Mistrik; K. Murakami; T. Yamaguchi; J. Pistora; M. Horie; S. Visnovsky (pp. 225-229).

Deep lamellar diffraction gratings fabricated by etching a transparent quartz plate are studied using spectroscopic ellipsometry. The rigorous coupled-wave analysis is used to calculate the optical response of the gratings. Three parameters of the rectangular profile are determined by utilizing the least-square method. Detailed investigation of the spectral dependences demonstrates the uniqueness of the solution. Observing the spectral dependences of Wood anomalies suggests that even complicated profiles can be fitted with high authenticity.

Keywords: PACS; 06.20.Dk; 42.25.Fx; 42.70.Ce; 42.79.Dj; 42.82.BqOptical metrology; Scatterometry; Spectroscopic ellipsometry; Diffraction grating; Wood anomaly; RCWA

Depth profiling of the strain distribution in the surface layer using X-ray diffraction at small glancing angle of incidence by Y. Fujii; E. Yanase; K. Arai (pp. 230-234).

In the studies of residual stresses of surface materials by using X-ray, in-depth distribution of the strain in the surface layer is necessary to be analyzed. We, therefore, characterized the refractive index of the surface layer materials with complex refractive index, which changes continuously in depth, and derived the X-ray intensity propagating during the surface layer materials. We applied this analyzing method to the experimental results of X-ray diffraction at small glancing angle incidence, and obtained the depth profile of the strain in the surface layer. The derived analyzing method can be applied to the residual stress distribution analysis of the surface layer materials of which densities change continuously in depth as multi thin films, compound plating layers.

Keywords: PACS; 61.10.EqGlancing incidence X-ray diffraction; Strain distribution in the surface; Depth profiling

Determination of interface roughness of Gd films deposited on Si surface using improved wavelet transform of X-ray reflectivity data by Oleksiy Starykov; Kenji Sakurai (pp. 235-239).

An improved wavelet transform method for the analysis of specular X-ray reflectivity data has been developed. It permits the evaluation of the thickness and roughness of particular layers in the thin film without assuming a certain film structure. The advantage of this method is that it can be applied to the analysis of a multilayer with unknown chemical and physical properties. It is useful in the characterization of structures with a complex composition, particularly oxide or diffuse layers. The present approach was successfully applied to the study of experimental data obtained on Gd thin nanoparticle films.

Keywords: X-ray reflectivity; Wavelet transform; Nanoparticles; Thin filmsPACS; 61.10.Kw; 61.12.Bt; 68.35.Ct; 68.55.Jk

Preparation of pure boron coating film and its characterization by XPS and TDS by M. Oyaidzu; A. Yoshikawa; H. Kodama; Y. Oya; A. Sagara; N. Noda; K. Okuno (pp. 240-243).

A PACVD apparatus was designed and fabricated at Shizuoka University in order to prepare high-pure boron coating films. In the present study, some parameters, especially feeding gas concentration, substrate temperature and CVD input power, have been optimized to prepare pure boron coating films. It was found that the purity of boron coating film was controlled by the decaborane concentration of feeding gas and substrate temperature during the PACVD process, and each optimized values were 0.4 and 473K, respectively. The atomic composition of boron in the boron coating film under the optimized condition has been achieved to be 0.94.

Keywords: PACS; 52.77.dq; 81.05.je; 33.60.fyBoron coating film; Pure boron; Boronization; XPS; TDS

Influence of reacting nitrogen gas consistence on the properties of TiN films prepared by rf. magnetron sputtering by Y. Pihosh; M. Goto; A. Kasahara; T. Oishi; M. Tosa (pp. 244-247).

Structural and mechanical properties of the TiN films deposited on stainless-steel substrates by rf. magnetron sputtering have been studied. The TiN films of few hundreds of nanometers in thickness were fabricated, varying both the total pressure of the N₂/Ar reactive gas mixture and N₂ partial pressure in a chamber. It was found that the morphology of the TiN films strongly depended on the N₂ concentration of the working gas. A formation of the (200) phase was detected at 50% of N₂ concentration. The tribological properties of the deposited films strongly depended on the total pressure. A low frictional coefficient of 0.14 has been measured for TiN films deposited at 50% of N₂, at a total pressure 9Pa.

Keywords: PACS; 61.14 Rg; 62.20.Qp; 68.10.Cr; 68.55.Jkrf. Magnetron sputtering; TiN; Microstructure; Ttribology; Surface energy

Microstructures and mechanical properties evaluation of hard chromized austenitic Fe–Mn–Al alloys by Jyh-Wei Lee (pp. 248-251).

Engineering components with hard coatings usually exhibit improved service behavior and increased lifetime. Hard chromizing technique is employed to deposit chromium nitride and carbides layer on the surface of an austenitic Fe–30.6Mn–6.8Al–0.9C alloy. The (Cr, Fe)₂N1−_x and (Cr, Fe)₂₃C₆ phases are found on the chromized surface, while the internal part of chromized layer is (Cr, Fe)₇C₃ phase. The thickness of the chromized layer obeys the parabolic rate law. For the specimen chromized at 1000°C for 4h, the hardness of the coating is 19.6GPa. A mixed cohesive–adhesive failure and an adhesion strength quality related to HF2 are observed on the coating. The wear resistance of the chromized layer is also improved at least three times better than the substrate.

Keywords: PACS; 81.65; 81.40Fe–Mn–Al alloys; Hard chromizing; Chromium carbide; Scratch test; Wear test

Corrosion and cell adhesion behavior of TiN-coated and ion-nitrided titanium for dental applications by Her-Hsiung Huang; Chu-Hui Hsu; Szu-Jung Pan; Ju-Liang He; Chun-Cheng Chen; Tien-Ling Lee (pp. 252-256).

This study investigated the corrosion resistance and cell adhesion behavior of titanium nitride (TiN)-coated and ion-nitrided Ti substrates for dental applications. The TiN-coated specimen surface layer contained a TiN/Ti structure, while the ion-nitrided specimen contained a Ti₂N/TiN/Ti structure. The polarization curves in artificial saliva showed that the corrosion rate and passive current for the specimens ranked as: untreated Ti>ion-nitrided Ti>TiN-coated Ti. The polarization resistance obtained from the electrochemical impedance spectroscopy ranked as: TiN-coated Ti>ion-nitrided Ti>untreated Ti. After 24h osteoblast-like U-2 OS cell incubation on the specimens, the attached cell number occurred in the order: TiN-coated Ti>ion-nitrided Ti>untreated Ti. The TiN-coating and ion-nitriding treatments can improve the corrosion resistance and cell adhesion behavior of Ti.

Keywords: PACS; 81.15.-z; 81.65.-b; 81.65.KnCorrosion; Cell adhesion; TiN; Nitriding; Coating; Titanium

Local electronic and chemical structure at GaN, AlGaN and SiC heterointerfaces by Leonard J. Brillson; Shawn T. Bradley; Sergey H. Tumakha; Stephen H. Goss; Xiaoling L. Sun; Robert S. Okojie; J. Hwang; William J. Schaff (pp. 257-263).

Defects and intermediate chemical phases at nanoscale heterointerfaces of GaN, AlGaN, and SiC can dominate their macroscopic electronic properties. We have used low energy electron-excited nanoscale luminescence spectroscopy in combination with secondary ion mass spectrometry and internal photoemission spectroscopy to correlate interface physical and electronic properties for a variety of Schottky barrier and heterointerfaces involving these semiconductors. These results demonstrate the key role of initial surface processing and subsequent chemical interaction on the heterointerface electronic states, barriers, and carrier concentrations.

Keywords: PACS; 73.20.−r; 73.20.Dx; 73.30.+y; 78.60.HkSchottky barriers; Interface states; Cathodoluminescence; GaN; AlGaN; SiC

Characterisation of amorphous GaN films by J.B. Metson; B.J. Ruck; F. Budde; H.J. Trodahl; A. Bittar; K.E. Prince (pp. 264-268).

Amorphous GaN thin films have been deposited using an ion-assisted deposition technique. These films are typically 100–400nm in thickness and show promising optoelectronic properties. X-ray absorption near edge spectroscopy reveals that a significant amount of molecular nitrogen is trapped near the substrate–film interface, where the films show the least microcrystalline structure. Secondary ion mass spectrometry (SIMS) depth profiles through this interface reveal a complex structure where nitrogen concentration peaks at the interface and oxygen contamination of the film peaks a short distance into the films. Crystallinity increases with film thickness and with decreasing oxygen levels. Control of oxygen levels in the films reveals that indeed the amorphous nature of the films is tied to this oxygen content.

Keywords: PACS; 81:05.Je; 81:05.GcAmorphous GaN; Thin films; SIMS; Oxygen impurity

Effect of treatments of sapphire substrate on growth of GaN film by Masatomo Sumiya; Shunro Fuke (pp. 269-272).

We have studied the surface of sapphire substrate as the first hetero-interface for the growth of wrutzite GaN film. The surface of sapphire substrate was thermally roughened by annealing in H₂ or N₂ ambient at temperatures more than 1000°C. This surface plays a decisive role of nuclei site of low-temperature (LT) buffer layer for obtaining GaN film with smooth surface having Ga-face (+c) polarity. By changing the nitridation temperatures of the sapphire substrate, the polarity of GaN film can be controlled from +c to N-face (−c) polarity corresponding to smooth and hexagonal-facetted surface morphology of GaN film, respectively. This indicates that the role of LT-buffer layer might be to prevent the surface of sapphire from unintentional nitridation, which is likely to result in −c GaN film by lowering the substrate temperature.

Pt Schottky diode gas sensors formed on GaN and AlGaN/GaN heterostructure by Kazushi Matsuo; Noboru Negoro; Junji Kotani; Tamotsu Hashizume; Hideki Hasegawa (pp. 273-276).

Exposure of Pt/GaN and Pt/AlGaN/GaN Schottky diodes to H₂ gas at moderately high temperatures around 100°C resulted in marked increase of forward and reverse currents. Increase was much larger in the Pt/AlGaN/GaN diode than in the Pt/GaN diode. Rapid turn-on responses and somewhat slower turn-off responses were observed with reproducible response magnitudes. A rigorous computer simulation of I– V curves indicated that current changes are due to changes in the Schottky barrier height caused either by H-induced formation of interfacial dipole or by hydrogen passivation of interface states.

Keywords: GaN; AlGaN; Pt; Schottky; Gas sensor

Photoemission study on interfacial reaction of Ti/n-type GaN by T. Naono; J. Okabayashi; S. Toyoda; H. Fujioka; M. Oshima; H. Hamamatsu (pp. 277-280).

In order to understand the mechanism of ohmic-contact formation by the annealing of Ti electrodes on n-type GaN, we have investigated the changes in the energy-band structure of Ti/n-type GaN depending on annealing temperature using photoemission spectroscopy. Valence-band spectrum for an as-deposited sample was explained by the simple summation of Ti and GaN spectra. Spectral line shapes significantly changed by annealing at 500 and 700°C, suggesting the formation of a TiN layer. The peak shifts of Ga 3d and N 1s core levels are interpreted as the energy-band bending and interfacial reaction with the formation of the TiN layer. It is revealed that the ohmic-contact formation by the annealing is attributed to the formation of GaN with nitrogen vacancies, which is consistent with the current–voltage characteristics.

Keywords: PACS; 73.40.Ns; 73.30.+y; 79.60.Jv; 61.72.J; 79.60.−iTi/n-type GaN; Photoemission spectroscopy; Ohmic contact; Interfacial reaction

In situ X-ray diffraction study of crystallization process of GeSbTe thin films during heat treatment by Naohiko Kato; Ichiro Konomi; Yoshiki Seno; Tomoyoshi Motohiro (pp. 281-284).

The crystallization processes of the Ge₂Sb₂Te₅ thin film used for PD and DVD-RAM were studied in its realistic optical disk film configurations for the first time by X-ray diffraction using an intense X-ray beam of a synchrotron orbital radiation facility (SPring-8) and in situ quick detection with a Position-Sensitive-Proportional-Counter. The dependence of the amorphous-to-fcc phase-change temperature T₁ on the rate of temperature elevation R_et gave an activation energy E_a: 0.93eV much less than previously reported 2.2eV obtained from a model sample 25–45 times thicker than in the real optical disks. The similar measurement on the Ge₄Sb₁Te₅ film whose large reflectance change attains the readability by CD-ROM drives gave E_a: 1.13eV with larger T₁ than Ge₂Sb₂Te₅ thin films at any R_et implying a lower sensitivity in erasing as well as a better data stability of the phase-change disk.

Keywords: PACS; 81.30.Hd; 68.55.−aPhase-change; Crystallization; Amorphous; Synchrotron radiation; X-ray diffraction; GeSbTe thin film

High-resolution TEM characterization of MOVPE-grown (111)-BP layer on hexagonal 6H (0001)-SiC by T. Udagawa; M. Odawara; G. Shimaoka (pp. 285-288).

A BP layer was grown on the (0001)-surface of 6H-type hexagonal SiC substrate by atmospheric-pressure metalorganic VPE, and crystallographic feature of the resultant BP/SiC hetero-structure was evaluated by transmission electron microscopy (TEM) and transmission electron diffraction (TED). Analysis of the TED patterns from the hetero-structure gave the following epitaxial relationship: (0001), -SiC // (111), <110>-BP. Extra diffraction spots in the TED pattern indicated the presence of {111}-twins in the (111)-BP layer. High-resolution TEM observation also revealed the presence of random texture which involved irregular configuration of atomic planes in the (111)-BP layer at the hetero-interface with the (0001)-SiC. The MOCVD-grown (111)-BP layer was deduced to develop on the (0001)-SiC, accompanying the formation of the (111)-twins and of the random texture at the interface with the (0001)-SiC.

Keywords: PACS; 61.16.Bg; 61.72.Nn; 68.55.−aCharacterization; Metalorganic chemical vapor deposition; III–V Semiconductors

Morphological investigation of double positioning growth of (111)-boron phosphide (BP) on the (0001)-GaN by M. Odawara; T. Udagawa; G. Shimaoka (pp. 289-292).

A BP layer was grown on a (0001)-GaN by atmospheric-pressure metalorganic VPE procedure. The BP layer grew epitaxially on the GaN with relationship: (0001), 〈 a-axes〉-GaN//(111),〈110〉-BP. On the surface of (111)-BP layer, crystallites disposed with double positioning configuration were found. The presence of crystallite disposed with the double positioning indicated that the BP layer grew up on the GaN with the manner of “degenerated epitaxy�?. In the (111)-BP layer grown through “degenerated epitaxy�? manner, crystalline imperfections, such as {111}-twins were involved.

Keywords: PACS; 61.16.Bg; 61.72.Nn; 68.55.-aCharacterization; Metalorganic chemical vapor deposition; III–V semiconductors

Incorporation of SiO₂ for the band alignment control of Gd₂O₃/ n-GaAs(001) structure by Jun-Kyu Yang; Hyung-Ho Park (pp. 293-296).

Band alignment of Gd₂O₃ gate oxide films on n-GaAs(001) was controlled by the incorporation of SiO₂. The photoelectron binding energy shifts in Gd₂SiO₅ film could be interpreted with relative electronegativity of second nearest neighbor element. The surface and interface morphology of Gd₂SiO₅/ n-GaAs structure was smooth due to the absence of crystalline phase. Energy band gaps were estimated as ∼5.8 and 6.6eV for Gd₂O₃ and Gd₂SiO₅, respectively, by combining photoemission with absorption spectra. A decrease of leakage current density and a saturated accumulation capacitance indicate an enhanced band offset and small roughness in Gd₂SiO₅/ n-GaAs system.

Keywords: PACS; 73.40.Q (metal–insulator–semiconductor structures)GaAs; MOS; Gd; ₂; O; ₃; Silicate; Band offset

Influence of Si₃N₄ and ZnS films on transmittance of InAsSb/InAsPSb heterostructures by Y.Z. Gao; X.Y. Gong; W.Z. Fang; H.Y. Deng; G.J. Hu; M. Aoyama; T. Yamaguchi; N. Dai (pp. 297-300).

The transmittance of InAsSb/InAsPSb heterostructures is remarkably improved by depositing a Si₃N₄ top layer. This demonstrates its good anti-reflective property. A study of the influence of various factors on the transmittance of the heterostructures is performed. A comparison was made between the transmittances of the heterostructures under different conditions. The different effects of Si₃N₄ and ZnS top layers on the transmittance of the InAsSb/InAsPSb heterostructures are discussed.

Keywords: PACS; 68. 47. FgInAsSb/InAsPSb; FTIR; Si; ₃; N; ₄; ZnS; Deposition; Transmittance

Oxidization process of CVD diamond (100):H 2�1 surfaces by Jun Nakamura; Toshimichi Ito (pp. 301-304).

We have investigated atomic structures of B-doped microwave-plasma chemical vapor-deposited diamond (100) surfaces using an ultra-high-vacuum scanning tunneling microscope (STM). Most of STM images taken from the diamond surfaces at the very initial oxidization stage reflected the original surface atomic regularity of the diamond (100):H 2�1/1�2 structures while some of these images demonstrated a distinctive feature clearly differing from those of the original hydrogen-terminated surfaces. A further oxidization of the diamond surfaces resulted in the appearance of another specific feature in larger surface areas. Possible oxygen sites and oxidization process of hydrogen-terminated diamond (100) surfaces are discussed in relation to preferential oxidizations of CC dimer bonds, based upon our STM observations.

Keywords: PACS; 68.37.EfCVD diamond; Surface structure; STM; Oxygen-terminated surface; Hydrogen-terminated surface; (1; 0; 0)

Growth and characterization of P-doped CVD diamond (111) thin films homoepitaxially grown using trimethylphosphine by Hideki Wada; Tokuyuki Teraji; Toshimichi Ito (pp. 305-309).

We have homoepitaxially grown phosphorus-doped chemical-vapor-deposited (CVD) diamond (111) films using trimethylphosphine (TMP) as a more convenient dopant gas and have measured their electrical properties. On one hand, sheet Hall coefficients, R_H, obtained at various temperatures, T, above room temperature (RT) by AC Hall method were all negative and had the maximum in the | R_H|–1/ T plots, suggesting that two types of electrons with substantially different mobilities existed in the P-doped specimens. On the other hand, a hopping conduction with an activation energy of 0.013eV was observed below RT. A two-carrier model was proposed to consistently explain all of these data obtained. From a curve fitting procedure, we deduced the RT electron mobility of 100cm²/Vs in the conduction band, the activation energy of 0.59eV from the donor to the conduction band and the compensation ratio of 1.6%. The smaller carrier mobility was estimated to be ≈1cm²/Vs. It is found that TMP yields a much higher doping efficiency for n-type diamond synthesis, as compared with PH₃.

Keywords: PACS; 73.61.Cw; 78.66.Db; 81.15.GhDiamond; n-Type; Phosphorus; Trimethylphosphine; (1; 1; 1); Two-carrier model

Electrical properties of diamond p– i– p structures at high electric fields by M. Yamamoto; T. Watanabe; M. Hamada; T. Teraji; T. Ito (pp. 310-313).

Using photo-lithography and plasma etching processes, we have fabricated high-field-applicable diamond p–i–p structures. Current –voltage ( I–V) characteristics of devices thus fabricated, revealed rapid increases in current due to substantial impact excitations, whereas space-charge-limited currents such as I�? V² were observed at sufficiently high electric fields. There were substantial differences in I–V and electroluminescence (EL) properties observed above 1×10⁶V/cm between N-contained high-temperature/high-pressure-synthesized diamond and undoped chemical-vapor-deposited (CVD) diamond, indicating that these characteristics strongly depend on the Fermi level of the diamond i layer employed. Cathodoluminescence data were also compared with the EL data.

Keywords: PACS; 73.61.–r; 81.15.Gh; 81.65.CfDiamond; High electric field; p; –; i; –; p; structure; Fowler–Nordheim relation

Formation of wide and narrow optical-band-gap amorphous-CN_x:H films using i-C₄H₁₀/N₂ supermagnetron plasma by Haruhisa Kinoshita; Ryo Ikuta; Katsutoshi Sakurai (pp. 314-317).

Amorphous-CN_x:H films were formed using supermagnetron plasma CVD. In this experiment, the rf powers supplied to the upper electrode (UPRF) and lower electrode (LORF) were controlled to 10 and 5–800W, respectively. The optical band gap of the a-CN_x:H film was found to decrease largely from 2.6 to 0.22eV with the increase of LORF from 5 to 800W. The hardness increased from 5.9 to 27.5GPa with the increase of LORF from 5 to 200W, and then it decreased gradually to 10.7GPa with the further increase of LORF to 800W. FT-IR absorption spectrum showed strong CH stretching mode vibration at low LORF, i.e., films formed at low LORF included many hydrogens bonded to carbons. The photoluminescence (PL) was measured, and it was found that the wide optical-band-gap a-CN_x:H film formed at UPRF/LORF of 10/10W showed broad white PL.

Keywords: PACS; 61.41.+e; 61.43.Dq; 78.55.Kz; 81.15.GhAmorphous-CN; _x; :H; Plasma processing; Chemical vapor deposition; Supermagnetron plasma

Optical and structural properties of CVD-grown single crystal SiO₂ using optically detected XAS by T. Nakamura; N. Takahashi; N.R.J. Poolton; A.E.R. Malins (pp. 318-321).

Using a new method of low-temperature CVD preparation, very high quality single-crystal quartz can be grown at rates of up to 3μmh⁻¹. By employing synchrotron radiation methods, the optical and structural properties of these crystals can be interlinked and they are compared with those of high quality hydrothermally grown material. The luminescence excitation spectra, which are very sensitive to the quality of the material, are assessed for both band edge (excitonic) and core level Si L-edge excitations. For the most part, the optical and structural properties of the two types of sample are indistinguishable, verifying the high quality of the material grown by the new method. The only source of difference arises from a weak red luminescence band, thought to originate from NBOHC defects: in CVD material, the L-edges derived from this band reveal some degree of local lattice disorder.

Keywords: PACS; 81.15.Gh; 78.55.−m; 71.35.Cc; 61.10.HtQuartz; CVD; Luminescence; OD-XAS

Structural defects in SiO₂/SiC interface probed by a slow positron beam by M. Maekawa; A. Kawasuso; Z.Q. Chen; M. Yoshikawa; R. Suzuki; T. Ohdaira (pp. 322-325).

We studied structure of SiO₂/SiC interfaces grown by thermal oxidization using low energy positron beams. From the positron lifetime measurements, typical two lifetime components related to amorphous network and large open spaces are observed in SiO₂, while only bulk lifetime in SiC. The lifetime of positrons near the interface is similar to that of SiO₂ amorphous network and no lifetime components related to large open spaces are detected. From the Doppler broadening measurements, the momentum distribution, probably related to oxygen valence electrons, is enhanced near the interface. The above results imply that the interface region has less open spaces than SiO₂ involving many oxygen dangling bonds.

Keywords: PACS; 68.35.C; 78.70.BSiO; ₂; /SiC interface; Interface defects; Positron annihilation spectroscopy; Dry oxidation; Pyrogenic oxidation

Growth and morphological properties of β-FeSi₂ layers by S. Tanaka; A. Yamamoto; S. Makiuchi; T. Matsuyama; M. Rebien; W. Henrion; H. Tatsuoka; M. Tanaka; Z.-Q. Liu; H. Kuwabara (pp. 326-329).

β-FeSi₂ layers were grown on Si(111) substrates by reactive deposition epitaxy under the presence of an Sb flux, and the morphological properties of the layers were investigated. The microscopic observations showed that the layer roughness, R_a, was 30–100nm for the layers with a thickness of 44–540nm. It has been also demonstrated that the surface roughness can be well estimated by the spectroscopic ellipsometry (SE) measurements using an effective medium approximation (EMA).

Keywords: PACS; 68.55.Jk (structure and morphology, thickness); 68.35.Ct (interface structure and roughness); 68.35.Fx (diffusion, interface formation)Deposition process; Diffusion; Silicides; Structural properties; Transmission electron microscopy (TEM)

Growth and structural properties of Mg₂Si and Ca₂Si bulk crystals by Noriyuki Takagi; Yusei Sato; Tsuyoshi Matsuyama; Hirokazu Tatsuoka; Miyoko Tanaka; Chu Fengmin; Hiroshi Kuwabara (pp. 330-333).

Mg₂Si and Ca₂Si bulk crystals were grown, and their structural and morphological properties have been investigated. The Mg₂Si crystals without any cracks or voids were grown by an interdiffusion process between the deposited Mg atoms and Si bulk crystals in a vacuum. Single phase Ca₂Si bulk crystals were also grown by the interdiffusion process using Ca and Mg₂Si crystals. The structural properties and the growth evolution of the silicides are discussed in comparison with those of the silicide layers.

Keywords: PACS; 68.55.Jk (structure and morphology, thickness); 61.16.Bg (transmission, reflection and scanning electron microscopy (including EBIC)); 81.15.Ef (vacuum deposition); 68.35.Fx (diffusion, interface formation)Deposition process; Diffusion; Silicides; Structural properties; Transmission electron microscopy (TEM)

Chemical properties of an oxide nanoskin on a polymeric surface by Atsushi Hozumi; Naoto Shirahata (pp. 334-337).

Vapor phase chemisorption of 1,3,5,7-tetramethylcyclotetrasiloxane onto polyimide (PI) substrates and subsequent photooxidation using 172nm vacuum ultraviolet (VUV) light successfully produced a silicon dioxide (SiO₂) layer of molecular-scale thickness, that is, an “oxide nanoskin�? (ONS). This ONS was estimated to be around 1nm thick by high-resolution transmission electron microscopy. Due to the ONS coating, the surface acidity of the PI substrate increased markedly and its isoelectric point shifted from around pH 3.5 to 2.0, which was almost equal to that of a native oxide-covered Si (SiO₂/Si) substrate. PI surfaces both with and without the ONS were further modified using a vapor of fluoroalkylsilane (FAS). Based on contact angle analysis, the surface energy of the FAS/ONS/PI substrate was mostly consistent with that of a SiO₂/Si substrate covered with a self-assembled monolayer (SAM) composed of FAS molecules. Our ONS was found to be effective in fabricating a FAS-SAM on a polymer substrate.

Keywords: PACS; 81.15; 68.35.M; 68.18Oxide nanoskin; Vacuum ultraviolet; Silicon oxide; Polyimide

Optical characterization of sol–gel deposited PZT thin films by spectroscopic ellipsometry and reflectometry in near-UV and visible regions by Daniel Franta; Ivan Ohl�dal; Jan Mistr�k; Tomuo Yamaguchi; Gu Jin Hu; Ning Dai (pp. 338-342).

In this paper the results concerning the optical characterization of the PZT film are presented. The multi-sample modification of the optical method based on combining variable angle spectroscopic ellipsometry and near-normal spectroscopic reflectometry is used to obtain the spectral dependences of the optical constants of this film within the spectral region 190–1000 nm. Within the near-UV region the sharp features of the spectral dependences of the optical constants are found. These features are explained by the existence of the narrow bands of the 4d and 3d valence electrons of the transition metals Zr and Ti. Within the optical characterization of the PZT film the defects consisting of boundary roughness and refractive index profile are respected.

Keywords: PACS; 77.84.Dy; 78.20.Bh; 78.20.CiPZT films; Optical constants; Ellipsometry; Reflectometry

Zn₃N₂ compensated ZnTe films and ZnTe–ZnSe superlattices grown by hot wall epitaxy by S. Sakakibara; Y. Inoue; H. Mimura; K. Ishino; A. Ishida; H. Fujiyasu (pp. 343-346).

Nitrogen-doped (N-doped) p-type ZnTe films and ZnTe–ZnSe superlattices (SLs) were prepared on GaAs (100) substrates by hot wall epitaxy (HWE) using NH₃ gas and Zn₃N₂ as a codoping source. We have investigated the compensation effect of Zn₃N₂ and optimized the growth conditions. Then the nitrogen-doped ZnTe films and ZnTe–ZnSe superlattices of high crystal quality with a high hole concentration were obtained.

Keywords: PACS; 81.05.Ea; 81.15.KkZnTe; ZnSe; Superlattice; GaAs substrate; Hot wall epitaxy

Control of Zn composition (0< x<1) in Cd1−_xZn_xTe epitaxial layers on GaAs substrates grown by MOVPE by K. Yasuda; M. Niraula; H. Kusama; Y. Yamamoto; M. Tominaga; K. Takagi; Y. Aagata (pp. 347-350).

Cd1−_xZn_xTe epitaxial layers over the entire composition range ( x from 0 to 1) were grown on (100) GaAs substrates by atmospheric pressure metalorganic vapor phase epitaxy. A growth temperature of 560°C, and the group VI/II precursor flow rate ratio of 2 or larger enabled us to control the Zn composition strictly on the grown epilayers. Epitaxial layers with high crystal quality were obtained in a wide range of Zn composition. The double crystal rocking curves (DCRC) full-width at half maximum (FWHM) values were between 260 and 670 arcsec at the end points of alloy range. The low-temperature PL measurements showed distinct bound-exciton emissions and weak deep-level emissions.

Keywords: PACS; 73.61.Ga; 81.05.Dz; 81.15.KkCdZnTe; MOVPE; Optoelectronic devices

Improvement in the light emission characteristics of CdS:Cu/CdS diodes by H. Murai; T. Abe; J. Matsuda; H. Sato; S. Chiba; Y. Kashiwaba (pp. 351-354).

p-CdS:Cu/n-CdS thin-film diodes showed light emission of bright green by deposition of a CdS layer at a high substrate temperature and by the use of an ITO/SnO₂-coated glass substrate. XPS analysis showed that indium diffused into the CdS:Cu layer from the ITO layer at the ITO/CdS:Cu interface but that indium did not diffuse into the CdS:Cu layer at the ITO/SnO₂/CdS:Cu interface. Indium compensates the acceptor of Cu as a donor in CdS. The tin oxide layer prevented diffusion of In into CdS. Again, the deposition of CdS at a high substrate temperature may promote activation of Cu as an acceptor, and the Cu may form shallow acceptor levels. Therefore, it is thought that the bright green emission from the ITO/SnO₂-based diodes is due to shallow Cu acceptor levels.

Keywords: PACS; 73.40.Lq; 73.61.Ga; 81.05.Dz; 81.15.Ef; 85.30.Kk; 85.60.JbCdS thin film; Cu-doping; p-Type; CdS homojunction; Light emitting diode; ITO/SnO; ₂; substrate

Transport and magnetic properties of Ce-doped LaMnO₃ thin films by Takeshi Yanagida; Teruo Kanki; Bertrand Vilquin; Hidekazu Tanaka; Tomoji Kawai (pp. 355-358).

Ce-doped LaMnO₃ epitaxial thin films were fabricated by a pulsed laser deposition method in consideration of thermodynamics. Oxygen- or argon-atmosphere post-annealed films showed a metal–insulator transition and ferromagnetic property, and the transition temperature T_c was found to be significantly influenced by the post-annealing conditions at the T_c ranging from 200 to 300K. Moreover, the majority carriers within Ce-doped LaMnO₃ films were identified to be holes from Hall effect measurements.

Keywords: PACS; 71.30.+h; 75.70.Ak; 75.30.KzManganites; Thin films; Magnetic and transport properties; Metal–insulator transition

HRTEM observation of interface states between ZnO epitaxial film and Si(111) substrate by Y. Nakanishi; A. Miyake; H. Tatsuoka; H. Kominami; H. Kuwabara; Y. Hatanaka (pp. 359-364).

ZnO epitaxial thin films could be formed by oxidation of ZnS epitaxial thin films deposited on Si substrates by electron-beam evaporation. The orientation relation of the ZnO film was (0002), [11−20]ZnO//(111), [1−10]Si. The ZnS films were oxidized from its surface toward the surface of the Si substrate gradually. The ZnS film with a thickness of about 100nm was completely changed to ZnO by annealing at 720°C for 10min in O₂ atmosphere. By excess annealing, longer than 30min, an intermediate layer was formed at the interface between the ZnO layer and Si(111) substrate. Exciton emission with a peak at 3.27eV from ZnO became dominant and visible emission due to oxygen vacancy in ZnO disappeared by the annealing of the film at 800°C for 5h in O₂ flow.

Keywords: PACS; 68.55.−a; 78.55.Et; 78.55.−mZnO; ZnS; Si; Thin film; Epitaxial growth; Annealing; Interface state; Exciton; Photoluminescence

Deposition and structural properties of piezoelectric ZnO epitaxial film on p-InP (100) substrate for FBAR by Jae Joon Lee; Yong Bae Kim; Young Soo Yoon (pp. 365-368).

R.F. magnetron sputtering grown ZnO films on p-InP (100) substrates without any metallic bottom electrode were studied to investigate a possibility of this structure for FBAR application, although the substrate has a relatively high resistance. AFM images showed that the root mean square of the average surface roughness of the ZnO film was 5.88�, and X-ray diffraction and transmission electron microscopy (TEM) measurements showed that the ZnO film grown on the InP were textured (or epitaxy) films with strong (0001) preferential orientation. Auger electron spectroscopy and bright-field TEM measurements showed that the ZnO epitaxial films grown on InP at 200�C had no any significant interdiffusion problems. These results indicate that the ZnO epitaxial films grown on p-InP (100) at low temperature hold promise for FBAR devices based on compound semiconductors substrates, such as InP and InSb, without metallic bottom electrode.

Keywords: Piezoelectric; Semiconductors substrates; ZnO film

Sb excimer-laser doping in ZnO films prepared by oxidation of sulfide on Si by K. Ohara; T. Seino; A. Nakamura; T. Aoki; H. Kominami; Y. Nakanishi; Y. Hatanaka (pp. 369-372).

ZnO thin films were formed by oxidation of ZnS films on Si substrates. Sb doping of ZnO films was tried by laser irradiation of ZnO deposited with Sb. Although p-type ZnO:Sb film was not obtained, it was observed that the laser irradiation increased the near-ultraviolet (NUV) emission intensity, whereas the visible emission of oxygen vacancies decreased. Moreover, the resistance of the laser-irradiated ZnO:Sb films was higher than that of films without irradiation. These results show that Sb compensates the oxygen vacancy; as a result, the electrons are neutralized by holes generated by the dopant (Sb).

Keywords: PACS; 68.55.–a; 51.50.+v; 78.55.–m; 77.84.BwZnO; Conduction control; Thin film; Epitaxial growth; Laser doping

Homoepitaxial growth of ZnO films on ZnO (112�0) substrates by Y. Kashiwaba; H. Kato; T. Kikuchi; I. Niikura; K. Matsushita; Y. Kashiwaba (pp. 373-376).

Homoepitaxial growth of ZnO (112¯0) films was achieved on single crystal ZnO (112¯0) substrates by metal-organic chemical vapor deposition. The full width at half-maximum of grazing incidence diffraction measurement of film with thickness of 0.95μm was smaller than that of a single crystal ZnO substrate. The surface roughness was increased from 1.7 to 37.8nm with increase in thickness from 0.16 to 0.95μm. In the room temperature photoluminescence spectrum of a homoepitaxial film with thickness of 0.95μm, the intensity of green emission due to intrinsic defects was weak and the band-edge emission due to free exciton emission was dominantly observed at 3.284eV.

Keywords: PACS; 81.05.Dz; 81.18.Kk; 61.10.Nz; 68.37.Ps; 78.55.EtZnO; Homoepitaxial growth; X-ray diffraction; MOCVD; Photoluminescence

Characterization of homoepitaxial and heteroepitaxial ZnO films grown by pulsed laser deposition by Z.Q. Chen; S. Yamamoto; A. Kawasuso; Y. Xu; T. Sekiguchi (pp. 377-380).

Homo- and heteroepitaxial ZnO films were grown on ZnO (0001) and Al₂O₃ (112�0) substrates by using pulsed laser deposition. The X-ray diffraction and Raman measurements for these films show good correspondence with the bulk ZnO substrate, which confirms successful growth of c-axis oriented ZnO layer. Strong UV emission was also observed in these films, indicating good optical quality. However, the surface roughness differs very much for the homo- and heteroepitaxial film, that is, much less for the homoepitaxial layer. Positron annihilation measurements reveal a higher vacancy concentration in the homoepitaxial layer.

Keywords: PACS; 81.15.F; 68.37.–d; 68.55.–aZnO; Pulsed laser deposition; Film

Growth and characterization of Zn1−_xCd_xO films using remote plasma MOCVD by Junji Ishihara; Atsushi Nakamura; Satoshi Shigemori; Toru Aoki; Jiro Temmyo (pp. 381-384).

Zn1−_xCd_xO films were successfully grown by remote plasma enhanced metalorganic chemical vapor deposition (RPE-MOCVD) with diethyl zinc, dimethyl cadmium, and oxygen plasma. The Cd composition x in the Zn1−_xCd_xO films was tuned by changing a flow rate of group-II sources. With increasing the Cd composition x, the crystal structure was changed from wurzite (WZ) to rock-salt (RS). The optical band-gap of the Zn1−_xCd_xO films with the wurzite structure up to x≤0.7 varied from 3.3eV down to 1.9eV.

Keywords: PACS; 78.55.Et; 81.15.GhRemote plasma enhanced metalorganic chemical vapor deposition; Zn; 1−; _x; Cd; _x; O; Diethyl zinc; Dimethyl cadmium

Growth of Mg_xZn1−_xO films using remote plasma MOCVD by Atsushi Nakamura; Junji Ishihara; Satoshi Shigemori; Toru Aoki; Jiro Temmyo (pp. 385-388).

Mg_xZn1−_xO films were successfully grown on a-plane sapphire (112¯0) substrates by remote plasma enhanced metalorganic chemical vapor deposition (RPE-MOCVD). Diethyl zinc (DEZn), bis-ethylcyclopentadienyl magnesium (EtCp₂Mg) and oxygen plasma were used as source materials. By increasing Mg content in the films, the crystal structure was shifted through a mixed state from wurtzite to rock-salt with no significant segregation. Both optical absorption edges and emission peaks of Mg_xZn1−_xO films shifted to the higher energy by increasing the Mg content at room temperature, showing an alloy broadening. The Stokes’ shift of wurtzite Mg_xZn1−_xO alloy films was quantitatively evaluated, resulting in a linear dependence on the absorption edge energy.

Keywords: PACS; 81.05.Dz; 81.15.GhRemote plasma enhanced MOCVD; Mg; _x; Zn; 1; −; _x; O; Diethyl zinc (DEZn); bis-Ethylcyclopentadienyl magnesium (EtCp; ₂; Mg); Stokes shift

Nano-photocatalytic decomposition of a stearic acid film deposited on the TiO₂ by an atomic force microscope by Kenkichiro Kobayashi; Yasumasa Tomita; Kazutaka Matsuhisa; Yuji Doi (pp. 389-393).

Stearic acid films have been deposited on single crystalline TiO₂ (110) substrates by vacuum evaporation. No changes are seen in AFM topographic images of the stearic acid films after the scan at a bias voltage of −10 to 10V in the dark. Similarly, ultraviolet irradiation at a bias voltage <0.0V brings about no changes of the AFM topographic images. In contrast, a rectangular hole with the size of 200nm×200nm is formed in the stearic acid film after the scan at 10V under ultraviolet irradiation. No current flows on the stearic acid film, whereas an appreciable current flows at −2.0V at the rectangular hole. The formation of the rectangular hole results from the field-assisted photocatalytic decomposition of the stearic acid film by AFM.

Keywords: Lithography; Photocatalysis; TiO; ₂; Atomic force microscope

Impact ionization phenomenon in single-crystalline rutile TiO₂ by H. Hashimoto; T. Teraji; T. Ito (pp. 394-398).

Titanium oxide (TiO₂) is known as a material suitable for photocatalysis, where photo-excited high-energy holes in TiO₂ play an important role. We applied high electric fields for TiO₂ to generate high-energy holes using an impact ionization phenomenon. In current–voltage ( I– V) measurements, currents rose suddenly at a threshold voltage, indicating that an impact ionization phenomenon occurred in TiO₂. The threshold voltage was controllable from 10 to 170V by varying the metal electrode thickness. This means that an electric field enhancement effect was significant at the edge of the thin film electrode. At higher voltages, there was observed a relation I�? V², indicating that space-charge-limited currents dominated the currents flowing in the specimen.

Keywords: PACS; 72.20.Jv; 72.20.HtTiO; ₂; Impact ionization; Space-charge-limited current; Photocatalysis

Titanium dioxide surface stoichiometry and ordering studied by resonant photoemission spectroscopy by S. Bourgeois; B. Domenichini; Z. Li; P.J. M�ller (pp. 399-402).

The electronic structure of titanium dioxide surfaces having undergone different preparations leading to different stoichiometries and crystallinities has been studied using resonant photoemission spectroscopy. Valence band photoemission spectra through the Ti 3p–3d/4s absorption edge between 45 and 55eV were measured and allowed a characterization of defects present at the surface as well as of the quality of the surface organization. Indeed, from the comparison of the resonance results obtained for each kind of surface with the LEED patterns on the one hand and the corresponding Ti 2p core level lines on the other hand, it was evidenced that the high binding energy part of the valence band seems rather related to the ordering of the surface than to the amount of defects.

Keywords: PACS; 68.35; 73.20TiO; ₂; surface; Photoemission; Synchrotron radiation

Reactivity between molybdenum and TiO₂(110) surfaces: evidence of a sub-monolayer mode and a multilayer mode by B. Domenichini; P. Kr�ger; A. Brevet; S. Bourgeois; Z. Li; P.J. M�ller (pp. 403-407).

Small amounts of molybdenum (from 0.03 to 1.3eqML) were deposited on non-stoichiometric TiO₂(110) surface. The deposits were investigated by means of LEED and X-ray/UV photoemission using synchrotron radiation. For the smallest coverage (<0.2eqML), deposition leads to oxidation of molybdenum into species close to Mo⁴⁺. In such a case, states appearing in TiO₂ band gap are mainly due to reduced titanium. For higher coverages, metallic behaviour of molybdenum is observed. This phenomenon was explained, thanks to first principle calculations, as a decrease of the Mo–O interactions for the benefit of the Mo–Mo interactions as the surface molybdenum atom density increases.

Keywords: PACS; 68.35.Ct; 68.47.Gh; 68.37.LpMolybdenum; TiO; ₂; surface; Photoemission; Synchrotron radiation; VASP

Photocatalytic chemisorption of water on titanium dioxide thin films obtained by radio frequency magnetron deposition by L. Sirghi; Y. Hatanaka; T. Aoki (pp. 408-411).

The photocatalytic chemisorption of water on titanium dioxide (TiO₂) thin films was studied by photocurrent decay experiments on the films exposed to water vapour. The TiO₂ films were deposited on quartz substrates by sputtering of a high purity TiO₂ target in a radio frequency magnetron discharge in argon–oxygen gas. In vacuum (10⁻²Torr), the films with good photocatalytic activity had large induced photocurrent intensity and long electrical charge carrier lifetime, when compared to the films with low photocatalytic activity. The photocurrent decay in good photocatalytic films exposed to water–argon gas mixture at atmospheric pressure depended strongly on the gas humidity, larger decay rates being observed at larger humidity values. Because of the oxygen chemisorption, the photocurrent decay rates were larger in air than in the same humidity water–argon gas.

Keywords: PACS; 92.20.Kv; 82.65.+r; 68.43.−h; 72.20.JvWater photocatalytic chemisorption; Titanium dioxide; Photocurrent decay

Structural and compositional characterization of N₂–H₂ plasma surface-treated TiO₂ thin films by L. Miao; S. Tanemura; H. Watanabe; S. Toh; K. Kaneko (pp. 412-417).

The structural and compositional properties of three samples such as as-deposited single-phase anatase-TiO₂ polycrystalline thin films on slide glass substrates (No. 1), the sample surface-treated by N₂–H₂ mixed-gases plasma (No. 2), and the sample being additionally anneal-treated in N₂ gases (No. 3), are characterized by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The primitive lattice cells of three thin films are verified as distorted in comparison with that of bulk from the TEM results. This distortion of primitive lattice cell causes the increase of optical band gap for the films when we compared it with that of bulk, while the decrease of optical band gap should be attributed to the substitution of N into TiO₂. Higher concentration of nitrogen in sample No. 3 is confirmed by line-EDS profiles under scanning TEM (STEM) when compared with sample No. 2 and this confirms that plasma surface treatment is an effective way for N-doping in TiO₂.

Keywords: PACS; 81.65M; 68.55 ;52.25.V ;61.16.B ;71.20; 68.55.NTitanium dioxide; Thin films; Plasma-treated; TEM; Optical band gap; Chemical composition

Effect of Mn coating materials of the nano-powders on phase transition of the nano-grained BaTiO₃ ceramics by M.-B. Park; N.-H. Cho (pp. 418-421).

Nano-grained BaTiO₃ ceramics prepared from 40nm size BaTiO₃ nano-powders exhibited the cubic as well as the tetragonal phase, while the nano-grained BaTiO₃ ceramics prepared from the BaTiO₃ nano-powders coated with Mn had only the tetragonal phase. The variation of phase transition of the BaTiO₃ ceramics appeared to be significantly affected by the grain boundary features; the effect of the grain boundary features resulted in the phase transition from the cubic to the tetragonal phase in the nano-grained BaTiO₃ ceramics, even though the grain size was about 40nm. The chemical origin of the effect of grain boundary on the phase transition of the nano-grained BaTiO₃ ceramics was strongly suggested.

Keywords: BaTiO; ₃; Nano-grained ceramics; Grain boundary; Phase transition

Control of chemical and electrical features near the grain boundary of the semiconducting BaTiO₃ oxides by M.-B. Park; N.-H. Cho (pp. 422-425).

The chemical and electrical characteristics of the grain boundary of the polycrystalline semiconducting BaTiO₃ ceramics, which were synthesized by hot-press sintering Mn-coated semiconducting BaTiO₃ powders, were investigated in terms of process parameters such as the amount of coating materials. Diffusion kinetic parameters of diffusing ions at particular heat-treatment conditions were obtained by fitting experimental data with computer-simulated results as well as electrical features near the grain boundary of the ceramics. Electrical features of semiconducting oxides were calculated from chemical distribution near the grain boundary; these values are similar to those obtained from impedance analysis. It indicated that this synthesis method can be used for fine control of chemical and electrical features near the grain boundary of semiconducting oxides.

Keywords: BaTiO; ₃; Grain boundary; Diffusion kinetic parameters; Potential barrier height

Optical properties of NiO thin films prepared by pulsed laser deposition technique by Daniel Franta; Beatrice Negulescu; Luc Thomas; Pierre Richard Dahoo; Marcel Guyot; Ivan Ohl�dal; Jan Mistr�k; Tomuo Yamaguchi (pp. 426-430).

In this paper, the optical characterization of the NiO thin films prepared by pulsed laser deposition technique onto the quartz substrate were performed using multi-sample modification of the combined optical method based on measuring and interpreting the experimental data obtained by variable angle spectroscopic ellipsometry and spectrophotometry in reflected and transmitted light. A new dispersion model of the optical constants of the NiO films was also used. This dispersion model was based on parameterizing the joint density of states together with the Gaussian broadening. The defects consiting in boundary roughness and refractive index profile were taken into account in optical characterization of the NiO films too. The spectral dependences of the optical constants together with the parameters characterizing the defects of these films were determined.

Keywords: PACS; 78.20.Bh; 78.20.CiNiO films; Optical constants; Ellipsometry; Reflectometry

Optical properties of rough LaNiO₃ thin films studied by spectroscopic ellipsometry and reflectometry by Jan Mistrik; Tomuo Yamaguchi; Daniel Franta; Ivan Ohlidal; Gu Jin Hu; Ning Dai (pp. 431-434).

Optical characterization of sol–gel deposited lanthanum nickel oxide, LaNiO₃ (LNO) film on Pt-coated Si substrate was performed by spectroscopic ellipsometry and reflectometry. The sum of five Lorentz oscillators was used for LNO dispersion parameterization in spectral range from 190 to 1000nm. Two theoretical approaches: Raileigh–Rice theory (RRT) and effective medium approximation (EMA) were considered to account for the effect of LNO upper boundary roughness. Root mean square (rms) values of the heights of irregularities obtained by atomic force microscopy (AFM) and RRT were 2.09 and 5.62nm, respectively. Effective layer thickness in EMA approach was found to be 4.62nm. Higher values of roughness determined from optical methods with respect to the AFM may be assigned to the effect of convolution of AFM tip and boundary irregularities.

Keywords: PACS; 78.20.CiEllipsometry; Reflectometry; Optical constants; LNO; LaNiO; ₃

Ultraviolet enhanced Si-photodetector using p -NiO films by Jeong-M. Choi; Seongil Im (pp. 435-438).

We report on the properties of a heterojunction photodiode composed of p-type NiO and n-type Si. This photodetector was fabricated by evaporating NiO powders on Si (100) substrate. Our deposited p-NiO film was found to have a hole concentration of ∼10¹⁹cm⁻³ according to Hall measurements. Current–voltage ( I– V) characteristics of our photodiode were measured in the dark and under ultra-violet (UV)–vis light illuminations (290nm, 325nm, 460nm, 540nm, and 633nm) at room temperature (RT). The photo-responsivity of our photodiode appeared almost saturated even at 0 V, showing good photo-voltaic properties. The responsivity was as high as ∼0.36A/W at 0V and ∼0.40A/W at 30V for visible light (633nm) while it was 0.15A/W at 0V and 0.17A/W at 30V for UV (290nm).

Keywords: PACS; 73.61.Le.; 78.66.−w.; 85.60.Dw.Photodiode; I; –; V; characteristics; UV–vis light; Photo-responsivity

Inverted top-emitting organic light-emitting diodes using transparent conductive NiO electrode by Se-W. Park; Jeong-M. Choi; Eugene Kim; Seongil Im (pp. 439-443).

We report on a top-emitting organic light-emitting device (TE-OLED) using a thermally evaporated and semi-transparent NiO film as a top-electrode. Our TE-OLED was fabricated, basically taking the reverse sequence for the fabrication of a conventional bottom-emitting organic light-emitting device (BE-OLED). Since the resultant sheet resistance of our NiO was high (8kΩ/□) and its transmittance was only 50%, the resulting luminance (∼150cd/m²) and injection current (∼50mA/cm²) of our TE-OLED were much inferior to those of the BE-OLED device. However, its top-emitting was clearly observable and is thus concluded that our TE-OLED using thermally evaporated NiO, is quite promising if the NiO is controlled to have lower sheet resistance than the present value.

Keywords: PACS; 72.80.Le; 85.30.De; 85.60.JbTop-emitting organic light-emitting device (TE-OLED); Semi-transparent NiO; Thermally evaporated; Bottom-emitting organic light-emitting device (BE-OLED)

Electrical characteristics of V₂O₅ thin films formed on p-Si by sputter-deposition and rapid thermal annealing by M.H. Yoon; Seongil Im (pp. 444-448).

We report on the formation of V₂O₅ semiconductor thin films using rapid thermal annealing (RTA) on sputter-deposited amorphous VO_x. DC magnetron sputtering was used to obtain an initial amorphous VO_x film on p-Si substrate, followed by O₂- and N₂-RTA at two different temperatures of 400 and 500�C for 3min. According to X-ray diffraction results, O₂-RTA is more effective to achieve the semiconducting phase, V₂O₅ than N₂-RTA, which caused some electrically conducting phases such as V₄O₉ or V₆O₁₃ at 400�C. Electrical characterization on Au/vanadium oxide/p-Si structure exhibited ohmic-like behavior when the thin film mainly contains those metallic phases while the structures were strongly rectifying once the film consists of the semiconducting phase, V₂O₅.

Keywords: PACS; 68.55.Jk; 68.37.Ps; 84.37.+q; 85.30.KkRapid thermal annealing; V; ₂; O; ₅; Semiconducting properties; Oxygen stoichiometry

Thickness dependence of optical properties of VO₂ thin films epitaxially grown on sapphire (0001) by Gang Xu; Ping Jin; Masato Tazawa; Kazuki Yoshimura (pp. 449-452).

Vanadium dioxide (VO₂) films were epitaxially grown on α-Al₂O₃ (0001) by rf reactive magnetron sputtering. The effects of film thickness ranging from 3 to 150nm on optical properties were investigated. It revealed that the semiconductor–-metal phase transition temperature considerably decreases as film thickness decreases, in particular for the film with thickness less than 10nm. On the other hand, we found that the difference in visible transmittance between the two phases of VO₂ also varies with film thickness. For the films with thickness less than 50nm, the semiconductor phase exhibits lower visible transmittance than its metallic phase, while for those with thickness larger than 50nm the situation is reversed.

Keywords: PACS; 78.20.−e; 42.70.−aVanadium dioxide; Thin film; Energy-efficient window; Optical design

Nanocrystalline WO₃ films prepared by two-step annealing by Ahalapitiya H. Jayatissa; Anantharamprasad Dadi; Toru Aoki (pp. 453-457).

This paper describes the formation of nanocrystalline tungsten oxide thin films by two-step thermal annealing of vacuum evaporated tungsten oxide films. The films were annealed at different temperatures to form semiconducting WO₃ films suitable for gas sensor and other electronic device applications. It was found that the film annealed at 300�C have a uniform nanocrystalline structure compared with high temperature annealed films. When these nanocrystalline films were re-annealed in higher temperature region (>500�C), no any variation of surface morphology and crystalline structure was observed. These experimental results indicated that stable nanocrystalline WO₃ films could be prepared by two-step annealing.

Keywords: PACS; 78.55.−m; 78.40.−q; 78.30.−j; 74.25.Gz; 79.60.−i; 61.82.Rx; 61.10.−iNanocrystalline; Tungsten oxide; Thin films; Annealing; Raman spectroscopy

Effect of La and Zn addition on Y₂O₃:Eu phosphors by S. Sakuma; H. Kominami; Y. Neo; T. Aoki; Y. Nakanishi; H. Mimura (pp. 458-460).

(Y1−_xLa_x)₂O₃:Eu,Zn phosphors have been prepared by a citric acid gel method to develop a red-emitting phosphor with high luminance and good chromaticity under a low excitation voltage. The dependence of structural and luminescent properties on the composition ratio of La/Y and on the Zn addition was investigated. The La addition of x=0.1 improves structural, cathode luminescence (CL) luminance, CL efficiency and chromaticity for the (Y1−_xLa_x)₂O₃:Eu phosphors. Though the Zn doping has a tendency of further improvement in structure, CL luminance, CL efficiency and chromaticity, the Y₂O₃:Eu,Zn phosphor without La addition shows the best characteristic.

Keywords: PACS; 78.60Hk; 85.45FdCitric acid gel method; Red phosphor; Cathode luminescence; (Y; 1−; _x; La; _x; ); ₂; O; ₃; :Eu,Zn; Chromaticity

Study of active surface centers in electroluminescent ZnS:Cu,Cl phosphors by M.M. Sychov; S.V. Mjakin; Y. Nakanishi; V.G. Korsakov; I.V. Vasiljeva; V.V. Bakhmetjev; O.V. Solovjeva; E.V. Komarov (pp. 461-464).

Surface and luminescent properties of copper activated zinc sulfide phosphors were studied. It was shown that measurements of the distribution of active surface centers (DAC) provides a tool of precise study of the surface chemical composition as well as probe for surface structural defects. Correlation between phosphor synthesis and annealing conditions, donor–acceptor properties of its surface and its electroluminescent characteristics was shown.

Keywords: PACS; 68.35.Dv; 61.72.−y; 81.05.DzPhosphor; ZnS; Surface; Active centers

Characterization on thermal stability of ZnS:Mn²⁺/MPS/SiO₂ nano-phosphor film by H. Kubo; T. Isobe; H. Takahashi; S. Itoh (pp. 465-468).

When the screen-printed ZnS:Mn²⁺ nano-phosphor film is heated under ambient condition, the photoluminescence (PL) intensity due to the d–d transition of Mn²⁺ decreases with increasing temperatures. The coating of 3-mercaptopropyl trimethoxysilane (MPS) and SiO₂ around ZnS:Mn²⁺ nanoparticles is effective to suppress the decrease in the PL intensity by heating. This is explained by suppressing the oxidation of ZnS:Mn²⁺ nanoparticles and the carbonization of propyl chain in MPS by SiO₂ coating.

Keywords: PACS; 78.55.Et; 78.67.BfNano-phosphor; Nanocrystal; ZnS:Mn; ²⁺; Photoluminescence

Preparation of CaS:Cu,F thin-film electroluminescent devices with an emission including purple region by Shintaro Hakamata; Mami Ehara; Hiroko Kominami; Yoichiro Nakanishi; Yoshinori Hatanaka (pp. 469-472).

CaS:Cu,F thin films have been prepared aiming at development of purple-blue emitting thin-film electroluminescent (TFEL) device with high luminance. The dependence of structural and photoluminescent (PL) properties of CaS:Cu,F thin films on annealing temperature and time was investigated. It was found that the annealing at higher than 800�C was necessary. Moreover, improvement of crystallinity and PL properties of the films saturated for the annealing time longer than 10min. It is concluded, therefore that the annealing at higher than 800�C for about 10min is desirable. CaS:Cu,F TFEL devices was fabricated on Si substrate. The purple-blue EL with an obvious peak at 425nm was obtained from the device with 0.3at.% of Cu for the first time.

Keywords: PACS; 78.60.Fi; 78.55.−m; 78.66−w; 78.66.HfPL; EL; Si substrate; Buffer layer; Annealing; Insulating layer

Luminescent properties of SrGa₂S₄:Eu thin film phosphors deposited by two electron beam evaporation by Y. Arai; H. Kominami; Y. Nakanishi; Y. Hatanaka (pp. 473-476).

SrGa₂S₄:Eu thin film phosphors have been deposited on quartz glass substrates at substrate temperatures of 350–450°C by multi-source deposition method in which two electron beam (2EB) evaporation sources were used. The films were annealed between 750 and 850°C for 30min in H₂S atmosphere after the deposition. It was shown by XRD measurement that SrGa₂S₄ phase was not formed but crystalline GaS was included in an as-deposited film, therefore, PL and CL due to SrGa₂S₄:Eu were not observed. The SrGa₂S₄ phase was formed by the annealing. Photoluminescence (PL) and cathodoluminescence (CL) spectra of all annealed films showed green emission peaked at about 530nm. CL luminance of all the films increased as the substrate temperature was increased. But the dependence on annealing temperature was not observed. So CL luminance depended only on substrate temperature during deposition. However, the CL luminance did not depend clearly on the annealing temperature between 750 and 850°C. The SrGa₂S₄:Eu film deposited at 450°C and annealed at 850°C for 30min showed a CL luminance and CIE coordinates of 1700cd/m² and (0.27, 0.67), respectively under excitation with 3kV and 60μA/cm².

Keywords: PACS; 78.60.HkFED; SrGa; ₂; S; ₄; :Eu; Electron beam evaporation; Phosphor; Thin films; CL

Magnetic properties of Fe70−_xCo30−_yN x+_y thin films by Chia Ying Li; Jenq Gong Duh (pp. 477-480).

High saturation magnetization material in FeCo-based system is widely used in recording media and communication devices. With additional dopant, the magnetic property and structure can be significantly improved. Fe₇₀Co₃₀ films with various N₂ doping were prepared by DC magnetron sputtering in this study. To obtain magnetic properties, which are adjustable by coating parameter, composition control is critical in the fabrication process. The composition of Fe, Co and N was evaluated with an electron probe microanalyzer (EPMA) and the structure analyzed by X-ray diffraction (XRD) for the films with respect to different N₂/Ar ratio. The magnetic properties of saturation magnetization ( M_S), coercivity ( H_C) and resistivity ( �?) were also measured, exhibiting M_S=15–24.5kG, H_C<70Oe and �?=22–156μΩcm.

Keywords: PACS; 70.50.B; 75.60.N; 75.70; 81.15.C; 81.40.RFerromagnetic materials; High saturation magnetization; FeCoN; Biaxial anisotropy

Investigation on transport properties of strained La_0.85Ba_0.15MnO₃ thin films using hall measurement by Teruo Kanki; Takeshi Yanagida; Bertrand Vilquin; Hidekazu Tanaka; Tomoji Kawai (pp. 481-484).

La1−_xBa_xMnO₃ thin films (0.05≤ x≤0.2) with a tensile strain from substrate exhibit unusual film thickness dependence on the Curie temperature T_C. The T_C was found to increase up to room temperature with decreasing film thickness. In this study, the origin of the T_C enhancement is examined by performing Hall measurements. The carrier densities of various thick films were found to be almost constant value (∼6×10²⁰cm⁻³) at 10K, whereas Hall mobility drastically increased, from 5cm²/Vs for 729-nm thick film to 50cm²/Vs for 24-nm thick film. These results indicate that the T_C enhancement is induced by increase of carrier transfer due to lattice deformation of Mn–O–Mn networks.

Keywords: PACS; 71.30.+h; 75.47.Lx; 75.70.AkManganites; Thin films; Magnetic and transport properties; Hall effect

Magnetic domain wall structures in free-standing Fe(1 1 0) monolayers by Yoshifumi Takeda; Kohji Nakamura; Toru Akiyama; Tomonori Ito (pp. 485-488).

We performed first principles calculations for magnetic domain wall structures in free-standing Fe monolayers with lattice constants matching with those of bcc Fe(1 1 0) and W(1 1 0) substrates by using the full-potential linearized augmented plane-wave method that incorporates intra-atomic noncollinear magnetism. The self-consistent calculations predict atomically narrow domain walls with widths of about 8 and 14 Å for the monolayers with the lattice constants of the Fe and W, respectively. These results are qualitatively consistent with and support domain walls having a 6 Å width in the Fe monolayers on a W(1 1 0) substrate recently observed in spin-polarized scanning tunneling microscopy experiments.

Keywords: PACS; 75.60.Ch; 75.70.AkMagnetic domain wall; Fe(1 1 0) monolayer; First principles calculations

Domain structures of nanocrystalline Fe₇₈Si₁₀B₁₂ thin films by Z.G. Sun; H. Kuramochi; H. Akinaga (pp. 489-493).

In the nanocrystalline Fe₇₈Si₁₀B₁₂ thin film, a weak dense stripe domain structure is observed. Out-of-plane anisotropy accounts for the observed domain structure. Perpendicular shape anisotropy due to the formation of the island-like configuration by the annealing treatment and magnetocrystalline anisotropy due to the strong α-Fe(Si) (110) texture are considered to be the origin of the perpendicular anisotropy. A metastable domain structure, which is the superimposition of the fine dense stripe domain structures onto the in-plane wide basic domains, was also observed in the as-annealed sample. The metastable domain structure turns to a stable single-domain state after magnetization.

Keywords: PACS; 75.50Tt; 75.80; +; q; 68-37Rt; 75.70Kw; 75.70AkNanocrystalline materials; Domain structures; Magnetostriction; Magnetic force microscopy

Effect of Sr doping on LaTiO₃ thin films by B. Vilquin; T. Kanki; T. Yanagida; H. Tanaka; T. Kawai (pp. 494-497).

We report on the electric properties of La1−_xSr_xTiO₃ (0≤ x≤0.5) thin films fabricated by pulsed laser deposition method. Crystallographic measurement of the thin films showed the epitaxial c-axis perovskite structure. The electric property of LaTiO₃ thin film, which is a typical Mott insulative material in bulk, showed insulative behaviour, while the Sr-doped films showed metallic conduction suffering electron–electron scattering. Below x=0.1, the major carrier type was identified to be hole, and switched to electron with further increasing Sr-doping above x=0.15. In fact, the switching from p-type to n-type for La1−_xSr_xTiO₃ thin films is first demonstrated in this study. The transition suggests that effective Coulomb gap vanishes due to over-additional Sr doping.

Keywords: PACS; 71.27.+a; 71.30.+h; 73.50.−hMott insulator; Thin films; Electrical properties

Emission characteristics and application of semiconductor field emitters by H. Mimura; Y. Neo; H. Shimawaki; T. Matsumoto; K. Yokoo (pp. 498-503).

The paper describes emission characteristics of semiconductor cold cathodes such as Si-field emitters and metal-oxide-semiconductor (MOS) electron tunneling emitters, and shows that their characteristics reflect the semiconductor property or the electron transport in an incorporated semiconductor device. The paper also describes Smith–Purcell radiation experiment as one of the device applications of semiconductor field emitters.

Keywords: Field emitters; MOS cathode; Electron emission; Smith–Purcell radiation

Growth of ZnO and device applications by K. Iwata; H. Tampo; A. Yamada; P. Fons; K. Matsubara; K. Sakurai; S. Ishizuka; S. Niki (pp. 504-510).

The molecular beam epitaxy (MBE) technique was used for ZnO epitaxial growth and growth properties were evaluated. Intrinsic ZnO epilayers with mobility of 120cm²/(Vs) and carrier concentrations of 7×10¹⁶cm⁻³ were obtained. ZnO on Si, bandgap engineering using Se and nitrogen doping were carried out for research of device application using this growth technique. We found a large bowing parameter of 12.7eV in ZnOSe, new ZnOSSe semiconductor that is lattice matched to Si and able to change the bandgap from UV to IR, and co-doping phenomenon of N and Ga doped ZnO.

Keywords: PACS; 61.50.Nw; 61.72.−y; 61.72.Vv; 64.60.Lx; 64.75.+g; 67.57.Hi; 71.55.Gs; 72.80.Ey; 73.61.Ga.; 77.84.−s; 78.30.Fs; 79.55.EtZnO; ZnO on Si; ZnOSe; II–VI; MBE; Bandgap engineering; p-ZnO

Atomic layer deposition in porous structures: 3D photonic crystals by J.S. King; D. Heineman; E. Graugnard; C.J. Summers (pp. 511-516).

This paper reports recent results from studies of atomic layer deposition for the infiltration of three-dimensional photonic crystals. Infiltration of ZnS:Mn and TiO₂ are reported for SiO₂-based opal templates. It has been demonstrated that high filling fractions can be achieved and that the infiltrated material can be of high crystalline quality as assessed by photoluminescence measurements. The highly conformal and uniform coatings obtained in these studies are shown to contribute significantly to the photonic band gap properties. These investigations show the advantages of atomic layer deposition (ALD) as a flexible and practical pathway for attaining high performance photonic crystal structures and optical microcavities.

Keywords: Three-dimensional photonic crystals; Photoluminescence; Photonic band gap properties; Optical microcavities

Microcavity effects and the outcoupling of light in displays and lighting applications based on thin emitting films by Kristiaan Neyts (pp. 517-523).

The outcoupling of light from thin films with a high refractive index is a problem occurring in lighting and display applications based on different technologies. Three different solutions are suggested: one-dimensional microcavity structures, roughness in the emitting layer, and roughness in the substrate/air interface. The advantages and drawbacks of these principles have to be evaluated for different applications.

Keywords: PACS; 78.20.−e; 78.60.Fi; 42.70.JkMicrocavity; Interference; Thin films; Displays; Light outcoupling; Electroluminescence; OLED

Novel green thin-film electroluminescent devices utilizing ZnS nanocrystals doped with Tb compounds by T. Toyama; K. Yoshimura; M. Fujii; H. Haze; H. Okamoto (pp. 524-527).

Green emission from ZnS nanocrystals (NCs) doped with Tb compounds has been investigated employing a double insulating thin-film electroluminescent device (TFELD) structure which has been used for conventional ac-driven TFELDs. The EL emission mechanism is discussed, centered on the generation of electric-field-induced high-energy electrons in NCs. The influence of Tb concentrations and co-doping of Tb compounds on the device performance is presented. Finally, green EL emission with a maximum luminance of 30cd/m² at 90 V0–_p employing ZnS:Tb,O,F NCs as the active layer is demonstrated.

Keywords: PACS; 78.60.Fi; 73.63.Bd; 85.60.Pg; 81.15.CdElectroluminescence; Nanocrystals; Thin films; Display devices; Sputtering

Metal–semiconductor interfaces in CdTe crystals and modification of their properties by laser pulses by V.A. Gnatyuk; T. Aoki; Y. Hatanaka; O.I. Vlasenko (pp. 528-532).

Current–voltage characteristics (CVC) have been investigated in high-resistivity CdTe(111) crystals with different electrodes (Ag, In and Au) which were deposited before different surface treatments. An influence of laser irradiation with nanosecond KrF laser pulses on the metal–CdTe interfaces, has been studied. Laser irradiation of CdTe crystals before and after electrodes deposition transformed the structure of the near surface and interface regions, respectively, and changed CVC of the barrier structures. Irradiation of CdTe crystals from the In contact side resulted in In doping. The laser-formed In/CdTe/Au diode structures had good rectification properties and showed promise for nuclear radiation detectors.

Keywords: PACS; 73.40.Sx; 61.72.Vv; 81.40.Wx; 29.40.WkCdTe crystal; Laser irradiation; Doping; Barrier structure; Current–voltage characteristic; Nuclear detector

Effects of Zn-doping on red-luminescence in Eu-doped (Mg,Ca)S phosphor films by Seiichi Tokunaga; Akiyoshi Mikami (pp. 533-536).

For the improvement of emission efficiency, ZnS-doped Mg_0.8Ca_0.2S:Eu phosphor film was made using rf-magnetron sputtering method. When the concentration of ZnS in the film is 4%, the photoluminescence intensity is about three times higher than that of ZnS-non-doped Mg_0.8Ca_0.2S:Eu film with keeping pure red emission (∼650nm). The crystal planes are oriented in (200) direction and make a solid solution with ZnS. Enhancement in photoluminescence (PL) intensity is closely related to the change of the crystal quality.

Keywords: PACS; 78.55.EtSulfide; Photoluminescence; Phosphor; Sputtering

Effect of ITO surface state to the aging characteristics of thin film OLED by Y. Fukushi; H. Kominami; Y. Nakanishi; Y. Hatanaka (pp. 537-540).

Relationships between surface state of indium tin oxide (ITO) and luminescent properties, and aging characteristics of organic light emitting diodes (OLEDs) were investigated. Polycrystalline ITO surface used as the substrate of the thin film OLED was changed by chemical etching and ultraviolet (UV) irradiation. Initial properties of luminescent characteristics showed no significant difference between different ITO surface states. On the other hand, the device fabricated on UV irradiated ITO showed longer lifetime than that of without UV irradiation. We found that UV irradiation was effective for the aging characteristics of thin film OLED.

Keywords: PACS; 78.60.Fi (Electroluminescence); 81.65-b (Surface treatments)Thin film; Organic light emitting diode; ITO; Aging characteristics

Photocatalytic oxidation dynamics of acetone on TiO₂: tight-binding quantum chemical molecular dynamics study by Chen Lv; Xiaojing Wang; Govindasamy Agalya; Michihisa Koyama; Momoji Kubo; Akira Miyamoto (pp. 541-545).

The clarification of the excited states dynamics on TiO₂ surface is important subject for the design of the highly active photocatalysts. In the present study, we applied our novel tight-binding quantum chemical molecular dynamics method to the investigation on the photocatalytic oxidation dynamics of acetone by photogeneratedOH radicals on the hydrated anatase TiO₂ surface. The elucidated photocatalytic reaction mechanism strongly supports the previous experimental proposal and finally the effectiveness of our new approach for the clarification of the photocatalytic reaction dynamics employing the large simulation model was confirmed.

Keywords: PACS; 31.70.Hq; 71.15.Pd; 82.65.+r; 82.50.HpTitanium dioxide; Acetone; Excited state dynamics; Photocatalytic reaction dynamics; Tight-binding quantum chemical molecular dynamics

Spectroscopic ellipsometry study on TiO₂ thin films modified by N₂–H₂ plasma surface treatment by S. Tanemura; L. Miao; H. Watanabe; Y. Mori (pp. 546-549).

We analyzed successfully the refractive index, n, and extinction coefficient, k, of three samples such as as-deposited single-phase anatase–TiO₂ polycrystalline thin films on slide glass substrates (#1), the sample surface-treated by N₂–H₂ mixed-gases plasma (#2), and the sample being additionally anneal-treated in N₂ gases (#3), by spectroscopic ellipsometry (SE). The double-layered film configuration named as the surface and the bulk layers is employed in SE analysis.The optical properties of the surface layer are confirmed to be important to explain the significant red shift of the absorption edge of both surface-treated samples observed in the preceding report. Particularly, the obtained imaginary part of complex dielectric constant of the surface layer of the samples #2 and #3 shows significant difference from that of the sample #1. This is due to the absorptive transitions not by solely anatase–TiO₂ but by mixed formation of TiO2−_xN_x and TiN with metallic characteristics.

Keywords: PACS; 07.60.R; 81.65.M; 78.66; 78.20.CSE; TiO; ₂; Thin film; Complex refractive index; Complex dielectric constant

Photoresponse of surface oxygen defects on TiO₂(110) by Masaharu Komiyama; Yan-Jun Li (pp. 550-553).

Using scanning tunneling microscopy (STM), the local photoresponse of a rutile TiO₂(110) surface was investigated on the atomic scale. While the illumination of 325nm ultraviolet (UV) light excited almost all the areas on the (110) surface, steps and (1×2) ridges that are associated with oxygen deficiencies and a “rosette�? structure exhibited higher response intensities. Previously proposed photoexcitation mechanism involving oxygen defect states in the energy band gap is examined by exciting newly created defect sites. These sites did respond to the illumination, but interestingly, when the sites are being paired, only one of them were active for the visible light illumination.

Keywords: PACS; 82.65.Yh; 73.20.HbTitanium dioxide; STM; Photoexcitation; Oxygen deficiency; Visible light

Photocatalytic characteristics of hydro-oxygenated amorphous titanium oxide films prepared using remote plasma enhanced chemical vapor deposition by Y. Hatanaka; H. Naito; S. Itou; M. Kando (pp. 554-557).

The photocatalytic activity and photoconductive characteristics of hydro-oxygenated amorphous titanium oxide (a-TiO_x:OH) films prepared using remote plasma enhanced chemical vapor deposition (RPE-CVD) were studied. The a-TiO_x:OH films have OH groups, which when exposed to UV irradiation, show high photoconductivity. The photoconductivity is drastically affected by oxygen gas. The results suggest that the recombination states present in the film are non-activated by the OH endings in the dangling bond like the hydrogen endings in hydrogenated amorphous silicon. Oxygen-sensitive photoconductivity is useful for environmental sensor applications.

Keywords: PACS; 81.15-Gh; 68.55-aTiO; ₂; film; Remote plasma enhanced CVD; Photocatalytic activity; Amorphous semiconductor; Photoconductivity

Separation of nitrogen removal pathways in a steady-state NO + CO reaction on Pd(1 1 0): an angle-resolved desorption study by Y.-S. Ma; I.I. Rzeznicka; T. Matsushima (pp. 558-562).

Three surface-nitrogen removal processes, i.e. (i) N₂O(a)→N₂(g)+O(a), (ii) N₂O(a)→N₂O(g), and (iii) 2N(a)→N₂(g), were separately analyzed in a steady-state NO+CO+O₂ or NO+H₂ reaction on Pd(110) through angular and velocity distributions of desorbing products. Processes (i) and (ii) are predominant at low surface temperatures, whereas process (iii) becomes major at high surface temperatures.

Keywords: PACS; 82.65.JvNitrogen oxide; Nitrous oxide; Nitrogen; Decomposition; Palladium; Angular distribution

Chlorine gas sensors with high sensitivity using Mg-phthalocyanine thin films by Toshihiro Miyata; Tadatsugu Minami (pp. 563-567).

High sensitivity chlorine (Cl₂) gas detection has been realized by newly developed gas sensors using Mg-phthalocyanine (MgPc) thin films. The MgPc thin film gas sensors exhibited an increase of conductivity with exposure to Cl₂ gas. The sensing properties of the MgPc thin film gas sensors were strongly dependent on the preparation conditions of MgPc thin films. The highest sensitivity for Cl₂ gas was obtained in the gas sensor using MgPc thin film prepared under the optimized preparation conditions; substrate temperature of 180°C, evaporation temperature of 475°C and film thickness of 40nm. It was obtained that at operating temperature of 200°C, the sensitivity of the MgPc thin film gas sensor linearly increased with the Cl₂ gas concentration in the range of 0.18–35ppm.

Keywords: PACS; 73.61.PhGas sensor; MgPc; Cl; ₂; gas; Thin film

Effect of AZO film deposition conditions on the photovoltaic properties of AZO–Cu₂O heterojunctions by Hideki Tanaka; Takahiro Shimakawa; Toshihiro Miyata; Hirotoshi Sato; Tadatsugu Minami (pp. 568-572).

This report describes the effect of ZnO:Al (AZO) film deposition conditions on the photovoltaic properties of AZO–Cu₂O heterojunction devices. The devices were fabricated by depositing a transparent conducting AZO thin film on a Cu₂O sheet that functions as the active layer as well as the substrate. The photovoltaic properties of these devices were considerably dependent on deposition temperature, irrespective of the deposition method used to fabricate them. Maximum efficiencies of 1.2 and 1.0% measured under AM2 solar illumination were obtained in AZO/Cu₂O devices fabricated using AZO films deposited at a temperature around 200°C by pulsed laser deposition (PLD) and r.f. magnetron sputtering (r.f.MS), respectively. The improvement in properties resulting from an increase in the deposition temperature up to about 200°C is attributed to an improvement of crystallinity in the AZO films; the degradation resulting from an increase over 250°C is related to an increase of resistivity in Cu₂O.

Keywords: PACS; 72.40+wZnO; AZO; Cu; ₂; O; Photovoltaic; Solar cell

Unoccupied electronic band structure of conjugated molecular films interfacing polycrystalline gold surface by Alexei Komolov; Preben J. M�ller (pp. 573-577).

Thin films of Cu-phthalocyanine (CuPc) and of tri-oligo(phenylene–vinylene) end terminated by di-butyl-thiole (tOPV) were thermally deposited in situ in UHV on polycrystalline Au substrate surfaces. The surface potential, the surface work function and the structure of density of unoccupied electron states (DOUS) located 5–25eV above the Fermi level ( E_F) were monitored during the film deposition, using an incident beam of low-energy electrons according to the total current electron spectroscopy (TCS) method. Auger electron spectroscopy (AES) was used to monitor atomic composition of the surfaces under study. The deposition of the CuPc films resulted in formation of the DOUS structure typical for these films while the deposition of tOPV films of less than 2nm thickness resulted in formation of an intermediate DOUS structure which was replaced by a stable DOUS of tOPV along with a further increase of the deposit thickness. The electronic work function of the CuPc and the tOPV films changed during the film deposition until it reached a stable value of 4.4±0.1 and 4.3±0.1eV, respectively, at a film thickness of 8–10nm. The width of the interface dipole layer in the CuPc and the tOPV films interfacing with the Au surface did not exceed 2nm. Analysis of the TCS data allowed us to assign the major DOUS features of the CuPc and tOPV films under study.

Keywords: PACS; Condensed matter; Electronic propertiesSurface electronic phenomena; Electron-solid scattering and transmission elastic; Surface chemical reaction; Metal-organic semiconductor interfaces; Cu-phthalocyanine

Structure of mercaptoalcohol self-assembled monolayers on Au(111) by K. Tsukamoto; T. Kubo; H. Nozoye (pp. 578-583).

Structures of mercaptoalcohols (1-mercaptohexanol: C₆OH, 1-mercaptobutanol: C₄OH and 1-mercaptopropanol: C₃OH) were studied with scanning tunneling microscopy (STM) and density functional theorem (DFT) calculations. Three structures were observed depending on the exposure of mercaptoalcohols: the striped structure (stripe A), at low exposure, with the stripe distances of 2.30±0.07nm (8 a₀) for C₆OH, 1.73±0.05nm (6 a₀) for C₄OH, and 1.44±0.04nm (5 a₀) for C₃OH; the stripe structure (stripe B), at high exposure, with the stripe distances of 1.19±0.04nm (4 a₀) for C₆OH and 1.01±0.03nm (3.5 a₀) for C₄OH; and the randomly distributed cluster-like structures at the highest exposure. Stripe B was not observed for C₃OH. A (√3×√3) R30° related structure, which is the highest coverage structure for alkanethiols on Au(111), was not observed. The structures are uniquely determined by the formation of hydrogen bonding.

Keywords: PACS; 82.65.–I; 82.65 MyStructure; Mercaptoalcohol; Self-assembled monolayers; Au(1; 1; 1)

Chain length dependence of adsorption structure of COOH-terminated alkanethiol SAMs on Au(111) by Eisuke Ito; Kaoru Konno; Jaegeun Noh; Kaname Kanai; Yukio Ouchi; Kazuhiko Seki; Masahiko Hara (pp. 584-587).

We studied adsorption structures and adsorption states of COOH-terminated alkanethiols with different alkyl chain lengths in self-assembled monolayers (SAMs) by X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and near-edge X-ray absorption finestructure (NEXAFS) spectroscopy. In the SAM of 11-mercapto-undecanoic acid on an Au(111) surface, formation of a well-ordered monolayer was confirmed from the results of the S 2p XPS and STM observation, while this was not the case in the SAM of 6-mercapto-haxanoic acid. C K-edge NEXAFS results suggested that the orientation or conformation of the alkyl chain differs between two SAMs. These results indicate that the intermolecular interaction of the alkyl chains plays an important role for the formation of a well-ordered monolayer of COOH-terminated alkanethiols on Au(111).

Keywords: PACS; 61.10.Ht; 61.16.Ch; 68.55.JkSelf-assembled monolayer; Alkanethiol; COOH-terminated alkanethiol; XPS; STM; NEXAFS

Study of thin films of carrier-doped strontium titanate with emphasis on their interfaces with organic thin films by Naoki Sato; Youichiro Harada; Takahito Terashima; Ryoko Kanda; Mikio Takano (pp. 588-592).

Fifty nanometer-thick metal-doped strontium titanate (M:STO, M=La and V) films deposited epitaxially on single crystalline STO substrates were characterized in comparison with indium tin oxide (ITO) covered glasses, to check their applicability to optically transparent anode materials for organic optoelectronic devices. M:STO, in particular V:STO, films turned out to have distinct surface flatness, needfully low electric resistivities and notably large work functions. While their optical transmittances are lower than those of ITOs at this moment, we suggest that M:STO films have a potential to take the place of ITO films. Further, we have observed energy level alignments for copper phthalocyanine thin films at the interface of V:STO.

Keywords: PACS; 73.30.+y; 68.35.CtStrontium titanate; ITO; Transparent electrode; OLED; Energy level alignment

Energy level alignment at interfaces with pentacene: metals versus conducting polymers by N. Koch; A. Elschner; R.L. Johnson; J.P. Rabe (pp. 593-597).

Ultraviolet photoemission spectroscopy was used to determine the work function ϕ and the hole injection barriers Δ_h of interfaces formed between pentacene and two fundamentally different electrode materials: (i) conductive polymers comprising poly(3,4-ethylenedioxythiophene) and sulfonate moieties, and (ii) Au with chemisorbed Cl. ϕ of these substrates before pentacene deposition covers a wide range of 4.25–5.15eV for the polymers, and extends to 5.8eV for Au–Cl. Despite this huge variation in ϕ, Δ_h after pentacene deposition is found to be almost identical for all cases (≈0.35eV). The mechanism responsible for Δ_h being independent of initial surface ϕ is proposed to be an interfacial charge transfer reaction leading to cationic pentacene species. These findings are compared to interfaces between pentacene and clean metal surfaces, where Δ_h was found to decrease with increasing substrate ϕ.

Keywords: PACS; 73.30.+y; 79.60.Fr; 79.60.JvConducting polymers; Organic semiconductors; Interfaces; Electronic structure; Photoelectron spectroscopy

Large-scale calculations of solid oxide fuel cell cermet anode by tight-binding quantum chemistry method by Michihisa Koyama; Momoji Kubo; Akira Miyamoto (pp. 598-602).

Improvement of anode characteristics of solid oxide fuel cells is important for the better cell performance and especially the direct use of hydrocarbons. A mixture of ceramics and metal is generally used as anode, and different combinations of ceramics and metals lead to different electrode characteristics. We performed large-scale calculations to investigate the characteristics of Ni/CeO₂ and Cu/CeO₂ anodes at the electronic level using our tight-binding quantum chemical molecular dynamics program. Charge distribution analysis clarified the electron transfer from metal to oxide in both anodes. The calculations of density of states clarified different contributions of Ni and Cu orbitals to the energy levels at around Fermi level in each cermet. Based on the obtained results, we made considerations to explain different characteristics of both cermet anodes. The effectiveness of our approach for the investigation of complex cermet system was proved.

Keywords: PACS; 68.47.Jn; 71.15.Pd; 82.45.Fk; 82.47.EdSolid oxide fuel cell; Ni/CeO; ₂; Cu/CeO; ₂; Cermet anode; Tight-binding quantum chemical calculation; Large-scale calculation

Fabrication of organic static induction transistors with higher order structures by Joseph Chennemkeril Mathew; Naoki Hirashima; Masakazu Nakamura; Masaaki Iizuka; Kazuhiro Kudo (pp. 603-606).

Organic static induction transistors (SITs) were fabricated with a Au(source)/organic/patterned-Al(gate)/organic/patterned-Au(drain) structure employing a new concept, ‘spontaneous patterning of higher order structures’ (SPHOS). A selective mechanical exfoliation process was developed to replicate the pattern of gate electrode after a pre-patterned drain electrode. The I– V curve measured between the gate and the drain electrodes exhibited a good Schottky characteristic and the drain current of the SIT with higher order structure showed a clear modulation by the gate voltage.

Keywords: PACS; 73.61.P; 68.55.J; 73.40.S; 85.30.T; 85.60.JOrganic transistors; Static induction transistor; Nanostructures; Ultrasonic process; Transistor characteristics

Infrared spectroscopy of pentacene thin film on SiO₂ surface by Yoshinobu Hosoi; Koshi Okamura; Yasuo Kimura; Hisao Ishii; Michio Niwano (pp. 607-610).

The thin film of pentacene on a SiO₂ surface has been investigated by infrared spectroscopy in the multiple internal reflections (MIR) mode. It was found that the molecules in the monolayer are arranged with their molecular axes perpendicular to the surface, and that this arrangement is conserved during film growth up to a 70-nm thickness. In addition, the assignment of the infrared active vibrational modes is discussed.

Keywords: PACS; 68.55.Jk; 78.30.JwPentacene; Infrared spectroscopy; Film structure; SiO; ₂; surface

Preparation and properties of bovine serum albumin thin films by pulsed laser deposition by J. Sagawa; S. Nagare; M. Senna (pp. 611-614).

Thin films of bovine serum albumin (BSA) were prepared by near infrared (1064nm) pulsed laser deposition (PLD). The films comprised nanodots of 24±4nm as primary units at laser fluence below 0.5Jcm⁻². Deposition rate of BSA was determined using a quartz crystal microbalance (QCM). The film preserves primary structure of BSA, as confirmed by a matrix assisted laser desorption ionization time of flight mass spectrometer (MALDI-TOF-MS). When the fluence exceeded 10Jcm⁻², we observed partial decomposition of BSA with simultaneous change in the secondary structure of the BSA from α-helix to β-sheet. Fluence dependence of the BSA structure in the deposited layer was discussed in terms of the ablation mechanisms.

Keywords: PACS; 81.15.Fg (laser deposition); 82.45.Mp (thin layers, films, monolayers, membranes); 87.14.Ee (proteins)Pulsed laser deposition (PLD); Bovine serum albumin (BSA); Primary structure; Secondary structure; Photothermal processes

Structural and optical properties of 6,13-pentacenequinone film by D.K. Hwang; Kibum Kim; J.H. Kim; Duk-Young Jung; Eugene Kim; Seongil Im (pp. 615-618).

We report on the structural and optical properties of 6,13-pentacenequinone film deposited on n-Si by thermal evaporation at room temperature. According to X-ray diffraction, films were found to have good crystallinity and also to have two crystalline phases mixed. Photoluminescence (PL) spectra exhibited double peaks at 1.97 and 2.09eV while the corresponding (double) peaks related to highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) transition were observed from direct absorption spectra at 2.94 and 3.11eV. The PL intensity was very strong under a UV illumination. It also seems that such a large Stokes shift as ∼1eV exist in this organic crystal system. Au/organic/ n-Si structures using 6,13-pentacenequinone films on n-Si showed rectifying behavior but with a relatively high level of leakage current due to many traps in the organic film.

Keywords: PACS; 68.55.Jk; 78.20.Ci; 78.55.Kz; 85.30.Kk6,13-Pentacenequinone film; Photoluminescence; Absorption; Rectifying behavior

Transparent ultra water-repellent poly(ethylene terephthalate) substrates fabricated by oxygen plasma treatment and subsequent hydrophobic coating by Katsuya Teshima; Hiroyuki Sugimura; Yasushi Inoue; Osamu Takai; Atsushi Takano (pp. 619-622).

Wettability of solid surfaces with water is well-known to be governed by chemical properties and nanotextures of the surfaces. A proper nanotexture of surfaces enhances their hydrophobicity. In this study, a novel method consisting of two dry process techniques, that is, nanotexturing by an oxygen plasma treatment and subsequent hydrophobic coating by means of low temperature chemical vapor deposition or plasma-enhanced chemical vapor deposition, was employed to form ultra water-repellent polymer sheets. A nanotexture was formed on a poly(ethylene terephthalate) substrate surface via selective oxygen plasma etching. This surface nanotexture remained after the hydrophobic coatings using organosilane precursors. The surface-modified substrate was transparent and ultra water-repellent, showing a water contact angle greater than 150�.

Keywords: PACS; 81.40.−z; 81.65.−bUltra water-repellency; Oxygen plasma treatment; Low-temperature CVD; Plasma-enhanced CVD; Organosilane precursor

The secondary structure control of silk fibroin thin films by post treatment by I. Taketani; S. Nakayama; S. Nagare; M. Senna (pp. 623-626).

Silk fibroin (SF) thin film was prepared via colloid chemical routes (CC) and by pulsed laser deposition (PLD). Secondary structure of the CC film, as examined by FT-IR, was random coil. By a post treatment with methanol, it transforms to β-sheet. As for PLD films, the β-sheet structure of SF powder was mostly preserved as deposited. This suggests that the post treatment is effective to restore the original β-sheet structure in the thin films. Transformation from random coil to β-sheet is easier in the film on the substrate of polyethylene than Si(100) due to weaker affinity to silk fibroin.

Keywords: PACS; 68.55.−a; 81.40.−z; 87.14.EeSilk fibroin (SF); Secondary structure; Post treatment; β-sheet

Electronic-state control of amino acids on semiconductor surfaces by Masato Oda; Takashi Nakayama (pp. 627-630).

Electronic structures of amino acids on the Si(111) surfaces are investigated by using ab initio Hartree–Fock calculations. It is shown that among various polar amino acids, a histidine is the only one that can be positively ionized when hole carriers are supplied in the Si substrate, by transferring the hole charge from Si substrate to an amino acid. This result indicates that the ionization of a histidine, which will activate the protein functions, can be controlled electrically by producing amino acid/Si junctions.

Keywords: PACS; 85.30.De; 87.83.+aProtein; Amino acid; Bio-device; Surface; Carrier injection; Ab initio calculation

Density functional theory studies on decomposition of ethyl-palladium complexes: an important role of cationic species by Rado Raharintsalama; Hiroaki Munakata; Michihisa Koyama; Momoji Kubo; Akira Miyamoto (pp. 631-635).

Density functional theory calculations were applied to investigate the β-hydrogen-elimination of the ethyl-palladium complexes, cis-(Me₃P)₂(Et)PdHX, where X=Cl, Br or I, to form ethene and hydrido-palladium complexes. Effects of substitution of halogen ligands and coordination of solvent molecules on geometric parameters and energies were investigated. Studies on solvated reaction intermediates revealed the agostic ethyl-palladium complexes to be important in the decomposition processes of the ethyl-palladium complexes.

Keywords: PACS; 31.10. +z; 31.15.Ew; 31.70.Dk; 33.15.Bh; 33.15.Dj; 82.30. −b; 82.30.Lp; 82.30.VyDensity functional theory; Agostic palladium complex; β-Hydrogen-elimination; Solvent effects; Cationic palladium complex

Development of new kinetic Monte Carlo simulator for hydrogen diffusion process in palladium–silver alloys by Hitoshi Kurokawa; Kazunori Bada; Michihisa Koyama; Momoji Kubo; Akira Miyamoto (pp. 636-639).

A novel kinetic Monte Carlo simulator “ARC�? was developed to investigate hydrogen diffusion process in metals and alloys. The results of the hydrogen diffusion coefficients in palladium, silver, and Pd1−_xAg_x ( x≤0.5) are in excellent agreement with experimental results. Two different diffusion sites, Pd-rich diffusion site and Ag-rich diffusion site, are found to be necessary to explain diffusion behaviors of hydrogen in palladium–silver alloys. Detailed analysis clarified that hydrogen atoms preferentially diffuse through the palladium-rich region of palladium–silver alloys at low silver concentrations, and that the hydrogen diffusion process at low silver contents is dominated by the jumps in palladium-rich regions. The migration barrier of hydrogen from Pd-rich diffusion site to Ag-rich diffusion site is estimated to be between 0.40 and 0.45eV.

Keywords: PACS; 05; 05.10.Ln; 66.30.FqKinetic Monte Carlo method; Palladium–silver alloys; Hydrogen diffusivity

Computational chemistry study of solid and aqueous solution interface by Ugur Mart; Changho Jung; Michihisa Koyama; Momoji Kubo; Akira Miyamoto (pp. 640-643).

Ionic properties at the solid–aqueous solution interface are investigated to monitor their effects on the hydration behavior and adsorption mechanisms on a MgO(001) surface by means of computational chemistry methods using density functional theory and molecular dynamics calculations. Especially, the dynamic behavior and dissociative adsorption of water molecules on the MgO(001) surface in the aqueous solution were successfully simulated. The results revealed that the ionic properties, such as electronegativity and ionic sizes, play an important role on their hydration behavior and interaction with oxide surfaces. Especially, MgO surface was found to undergo the hydroxylation due to the dissociated H⁺ and OH⁻ ions.

Keywords: PACS; 31.15.Ew; 31.15.Qg; 68.45.−v; 82.65.−iSolid–aqueous solution interface; Oxides; Hydration; Monovalent metal ion; Density functional theory; Molecular dynamics

Periodic density functional and tight-binding quantum chemical molecular dynamics study of surface hydroxyl groups on ZrO₂(111)-supported Pt catalyst by Changho Jung; Michihisa Koyama; Momoji Kubo; Akira Imamura; Akira Miyamoto (pp. 644-647).

Periodic density functional and tight-binding quantum chemical molecular dynamics calculations were employed to clarify the characteristics and dynamics of surface hydroxyl groups on Pt/ZrO₂ catalysts. We applied the periodic density functional theory calculations to the investigations on the effect of hydroxyl groups on the adsorption characteristics of Pt atom on ZrO₂(111) support and hydroxyl groups were found to decrease the adsorption energy of Pt atom on the ZrO₂(111) support. Furthermore, we applied our original tight-binding quantum chemical molecular dynamics method to the clarification of the dynamic behaviors of the hydroxyl group on the Pt/ZrO₂(111) and ZrO₂(111) surface. We found that the Pt atom triggers the migration and hopping of the H atom of the hydroxyl group. The migration of H atoms on the Pt/ZrO₂ catalyst was discussed in the sight of their catalytic activity.

Keywords: PACS; 31.15.Ew; 68.43.−h; 71.15.Pd; 82.65.+rPeriodic density functional theory; Tight-binding quantum chemical molecular dynamics; ZrO; ₂; Pt; Hydroxyl group

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Applied Surface Science (v.244, #1-4)

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Applied Surface Science (v.244, #1-4)