Flat monolayer clusters of platinum on graphite show one order of magnitude higher catalytic activity than taller Pt clusters for the H2-D2 exchange reaction. Significantly lower CO adsorption energy (73 kJ/mol) has also been found on the monolayer Pt clusters deposited on the terrace of the graphite surface. Based on the measurements of scanning tunneling microscopy, scanning tunneling spectroscopy and inelastic electron tunneling spectroscopy, the origin of such specific characteristics of the monolayer Pt cluster has been ascribed to the Pt-C hybridization, which leads to a shift of the d-band center of platinum away from the Fermi level.
Resistance Random Access Memory (ReRAM) is often made in the sandwiched structure where a transition metal oxide (TMO) film with polycrystalline structure is placed between the upper and the lower electrodes. Although whether resistance switching effect occurs in grains or in the grain boundary is key issue which decides the downsizing limit of memory cells, it has not been clarified yet. We prepared NiO/Pt structure using the DC sputtering method, and investigated the property of resistance change effect in the local area using conducting atomic force microscope. As a result, it was clarified that the resistance change occurred not in the NiO grain but in the NiO grain boundary. Therefore, it was suggested that the limitation of downsizing is decided according to the grain diameter.
The flow of the residual gas ion generated by a collision with high-energy electron in an axisymmetric gun was numerically investigated. Since the lifetime of the gun is dominated by the cathode damage induced by the ion bombardment, it is of industrial importance to reveal how the ions impinge on the cathode and how the inflow can be repelled. Under the normal operating condition of the electron gun (40 kV, 6 A), we determined the inflow basin, i.e. the region where the gas ions were born there and finally reached to the cathode. The basin consisted of four separated zones characterized by the potential distribution on the beam axis. To eliminate the downstream zones, it was useful to append a positive voltage imposed electrode behind the anode. The voltage necessary for repelling the ion inflow was found to be 300 V being less than 1% of the electron acceleration voltage.
This paper addresses the development of the surface finishing for a titanium material and the study for the reduction of outgassing property of adsorbed water (H2O) molecules. Developed surface finishing is composed of the buffing for the reduction of the surface roughness and improved chemical polishing for the thick surface oxide layer compared with the chemical polishing so far. The surface roughness of the surface finished titanium material is reduced 35% and the thickness of the surface oxide layer increases by 30%. The total amount of thermal desorbed H2O gas for the new surface finished titanium is reduced 30%. It is considered that the origin for the decrease of the amount of desorption H2O gas is the reduction of the adsorption sites due to the decrease of the surface roughness and the reduction of adsorption energy of H2O gas due to the strong surface oxidation for a titanium material.
A lot of aluminum (A2219-T852) flanges, which have a knife-edge seal, have been used at the SPring-8 storage ring. We investigated an Electron Beam Modified (EBM) knife-edge seal for the flange1) to confirm a seal compatibility with the original A2219-T852 flange. In comparison with the original flange, we found that a proof stress is almost equal, and the EBM flange has higher hardness and creep rupture stress.
Based on experiences in the precedent stain-less steel case, a possibility of employing copper-alloy and aluminum-alloy Matsumoto-Ohtsuka (MO)-type flanges in a vacuum beam pipes for a particle accelerator is experimentally studied. They can mitigate the heating problems found in the case of stainless-steel flanges under high-intensity beams, and also simplify the manufacturing procedure of beam pipes. Copper-alloy flanges show a comparable vacuum sealing property to the stainless-steel one, and several beam pipes with the copper-alloy flange has been successfully installed in the KEKB B-factory positron ring. The R&D on aluminum-alloy flanges has just started, and a promising result is obtained. Any coatings or treatments to improve the hardness of sealing part can be omitted if duralumin-series aluminum alloys are used. However, further detailed investigations are required about the hardness and stiffness properties of the gasket and flange materials before applying the flanges to the real machine.
Magnetically suspended turbo-molecular pumps (TMPs) have been widely used in nuclear fusion devices and sometimes used in particle accelerators, because it is much easier for the TMPs with dry backing pumps to achieve and maintain UHV without oil contamination. In these devices the TMPs are influenced by a quasi static magnetic field; the eddy current is induced on the rotating rotor and then forces the rotor to thermally expand. In order to use the TMPs safely we attempted to establish a standard procedure for determining the influence of magnetic fields on TMPs. First of all, this influence was investigated in detail through the experiment with a rather small TMP. As a result, the following are found. (1) The parallel magnetic field has no influence, on the other hand, the driving power and the rotor temperature are greatly affected by the vertical magnetic fields. (2) The eddy current loss is formulated and well estimated with a model where a localized magnetic field and current flow exist within the rotor into the region down to a substantial skin depth δ from the surface. This time we applied the above conclusions to the TMPs with high radioactive resistance which were employed in the 3-GeV rapid cycling synchrotron (RCS) in J-PARC (Japan Proton Accelerator Research Complex). With the evaluation equation of eddy current loss established through the experiment in a uniform magnetic field, the rise of rotor temperature is estimated to be ∼100°C even in the orthogonal magnetic field of 0.003 T. Thus, we concluded that the TMPs are safely operated in the RCS, as the leakage magnetic field at the floor where the TMPs are set is less than 0.001 T.
In this report we derive approximation of the transmission probability K for a cylindrical pipe which is usually given with computational calculation by using Monte Carlo technique nowadays, with rather old fashioned diffusion theory. Same results as Dushman's approximation is given based on the stationary solution of the one-dimensional diffusion equation with adopting the special boundary condition, that is the boundary of Dirichlet condition n=0 (n: number density of molecules) placing at the outer side of the real boundary (exit of the pipe). Transmission probability of the serially connected cylindrical ducts of different size is also given by those theory of diffusion.
We investigated the concept of creating a gas radial flow by employing the molecular drag effect upon gas molecules on rotating disks. All the gas molecules have a circumferential velocity rω (r: distance from the rotating axis, and ω: angular velocity) each time they leave a surface of the rotating disks. As a result, the gas molecules between the rotating disks tend on average to move outward from the center. That is, a radial flow appears. This idea was demonstrated by Monte Carlo simulation of 2 types of rotating disks (flat and corrugated ones). Pumping efficiency was clearly demonstrated for both types of disks when the velocity ratio rω/<v> (<v>: mean velocity) became larger than 1.
The back pressure of Turbo-Molecular Pumps (TMPs) is constantly monitored using Pirani gauges at J-PARC (Japan Proton Accelerator Complex) RCS (3-GeV Rapid Cycling Synchrotron) where they are used not only in rough pumping but also evacuations during beam operations. The gauge head needs to be very resistant to vibration and abrupt air inlet etc. in minimizing exposure to radiation during maintenance and hence a 50 μm in diameter W wire was adopted as the filament. This type of Pirani gauge has worked well in monitoring the back pressure of the TMP but it has become difficult to measure the low pressure of less than several Pa with the gauge, which may have been due to changes in the emissivity of the W surface. An attempt was therefore made to develop a gauge head made of Pt wire in allowing pressures as low as 0.1 Pa to be measured. Platinum is one of the best possible materials to use because it is very stable against oxidization. However, ordinary Pt gauge heads are rather weak when it comes to vibrations and abrupt air inlet due to its low tensile strength. In order to improve its toughness the filament was composed of twelve 100 μm in diameter Pt wires that were 65 mm long, resulting in it being capable of enduring a force of 25 N. All the wires were welded in series on metal poles in two separate glass plates, with the poles being electrically insulated. This resulted in the filament, 78 cm long and about 10 Ω at room temperature, being containable in a 5 cm in diameter and 10 cm long cylindrical envelope. The output from the gauge head was then examined as a function of pressure under constant current as the plan was for it to be controlled using the constant current method. Confirmation then took place that the pressures of 0.1 Pa up to 103 Pa were measurable with the gauge using current control in such way that the set value increased with pressure increases in three stages.
Densities of silane and hydrogen gas mixtures used for the production of thin silicon solar cell were measured using a quartz sensor, which output depends on viscosity and molecular weight of gas measured. The measurement for the silane-hydrogen gas mixtures revealed that the quartz sensor output depends on the silane and hydrogen densitites, can derive each density in the mixtures. From the results of the measurement, working curves were dereived for the pressure of 133-1333.0 Pa for the industrial production at room temperature. Resolusions of the density measured are 0.03 vol.% at total pressure of 1333.0 Pa, and are comparable to the results by a quartz pressure gauge previously reported. Finally, it was shown that the silane density ratio does not agree with the silane flow ratio, indicating that in-situ silane density measurement is important to control silane density.
Capacitively coupled capillary Ar and He plasmas have been generated in a quartz tube with the inner/outer diameters of 1.0/3.0 mm at the RF (13.56 MHz) powers of 3-7 W using the externally attached parallel-plate electrodes. Plasma expansion along a tube axis was a maximum at a gas pressure of 10-20 kPa, in which Vpp was a minimum and so Paschen's minimum condition was satisfied. The capillary plasma was magnetized by a strong magnetic field of 0.4 T to sustain the plasma at a low pressure, since the plasma did not ignite at the gas pressure below 2-4 kPa. The optical emission spectrum analysis revealed that atomic excitation temperature increased with decreasing gas pressure. Furthermore, it was found that the metastable atoms play an important role in the plasma sustenance at a high gas pressure.
An electron cyclotron resonance ion source (ECRIS) has been designed and developed for a synthesis of new materials such as endohedral metallofullerenes. The plasma chamber diameter is 140 mm in order to produce large m/q ions, like singly charged C60 ions effectively. In this study, we examined the performance of our ECRIS by plasma measurements using a Langmuir probe. The plasma density increased with increasing Ar pressure and reached to 6.1×1017 m-3 at a pressure of 5.0×10-3 Pa. The plasma was produced over a large volume compared with conventional ECRISs.
To demonstrate experimental evidence caused by the lattice strain that was induced by the surface steps introduced by electronic stimulated desorption of ionic-crystals, the ion scattering experiment has been performed. Surface-channeling of protons incident with 5 mrad on an electron-irradiated KBr(001) surface is investigated using a 0.55 MeV beam of protons. The direction of the incident beam is adjusted along the <100> channeling condition and the channeling-dips of the scattering yields are observed. The electron dose-dependence of the minimum yields (χmin) and widths of the dips (φ1/2) are compared with those measured on a KCl(001) surface. For the results of the χmin and φ1/2, results of KBr and KCl show similar dependence on the irradiation dose. For the both surfaces, two small peaks appear in symmetric positions on the channeling-dips. Peak-separations between the two peaks and widths of the peaks increase with the irradiation dose. Although no difference of the lattice strain induced on the two surfaces is detected only by the present experimental results, slight difference between the results for the two surfaces is observed and it is expected to be related with experimental evidence to demonstrate the lattice strain.
Organic thin films were prepared with pyromellitic dianhydride (PMDA) and oxydianiline (ODA) by vacuum evaporation with or without argon plasma, and molecular structures and surface morphologies of the PMDA, ODA, polyamic acid (PAA) and polyimide (PI) thin films were analyzed. The surface roughness decreased due to the plasma during the deposition. Oxygen content of the PMDA thin film prepared with the plasma decreased compared to that without the plasma. However, the PMDA thin film prepared with the plasma had a hydrophilic surface compared to that without the plasma. All of these organic thin films prepared with the plasma had hydrophilic surfaces compared to those without the plasma. Surface roughness of these thin films has a smaller effect on the wettability than hydrophilic moieties.
Organic field effect transistors are fabricated by the active layer of Regioregular poly (3-hexylthiophene-2,5-diy)(P3HT) thin film. CYTOP thin film made from Amorphous Fluoropolymer and fabricated by spin-coating is adopted to a gate dielectric layer on Polyethylenenaphthalate (PEN) thin film that is the substrate of an organic field effect transistor. The surface morphology and molecular orientation of P3HT thin films is observed by atomic force microscope (AFM) and X-Ray diffractometer (XRD). Grains are observed on the CYTOP thin film via an AFM image and the P3HT molecule is oriented perpendicularly on the CYTOP thin film. Based on the performance of the organic field effect transistor, the carrier mobility is 0.092 cm2/Vs, the ON/OFF ratio is 7, and the threshold voltage is -12 V. The ON/OFF ratio is relatively low and to improve On/Off ratio, the CYTOP/Polyimide double gate insulating layer is adopted to OFET.
Effects of substrate bipolar pulse voltage (Vs), pulse frequency and duty ratio on the properties of Cu thin films using magnetron sputtering with multipolar magnetic plasma confinement assisted by inductively coupled plasma (MMPC-ICP) were demonstrated. Results from X-ray diffraction (XRD) show that the intensities of the Cu(111) and Cu(200) peaks depend strongly on the Vs. The intensity of the XRD peak for Cu(111) increased when the Vs was increased from 0 V to −120 V. It is shown that the Cu film deposited at Vs=−120 V has a maximum grain size of about 42.6 nm; this value is about 1.5 times higher than that at Vs=0 V.
The threshold of secondary electrons in photoelectron yield spectroscopy (PYS) was examined using numerical calculations based on Fowler's formula, and was measured on a Cu(111) surface as a function of the surface temperature. In the numerical calculations, the yields are affected by surface temperature at around the threshold. The yield to the power of 1/2 shows a linear relationship of over 0.04 eV per 100 K from the threshold as a function of energy. The estimated threshold shifts to a lower energy with increasing surface temperature, by 0.003 eV per 100 K. The estimated thresholds also decrease with increasing value of the multiplier of n in Fowler's formula. In experiments, the threshold of Cu(111) at room temperature is estimated to be 4.8 eV±0.05 eV. The amount of change in the threshold caused by variation in surface temperature is interpreted in terms of the effects of the intrinsic Fowler's formula and lattice expansion.
Fine cell-adhesion patterning and nuclei orientation control on silicone rubber were investigated by limiting line-width of carbon negative-ion implantation. The ions were implanted at 3×1015 ions/cm2 and 10 keV through masks of ridge-pattern and rectangle-pattern with various slit apertures of 0-40 μm in width. After 2 days culture, nuclei of rat mesenchymal stem cells were stained with fluorescent dye to evaluate the nuclei positions at each tip ridge-region and the relative angles between the major axis of ellipse-shape nuclei and the implanted line-region. Results showed the individual nucleus arrangement along the narrow line-widths of 3-12 μm and the gathered one on the wider line-width. Number of nuclei orientation in the angle range of 0°-10° increased to 79% on the line-width of 10 μm. As a result, the fine cell-adhesion patterning and nuclei orientation could be achieved by decreasing the implanted line-width to 10 μm.
Aerosol Deposition is a promising process for fabrication of thick and dens ceramic coatings. Therefore, this process has been developed for fabrication of ceramic coatings especially lead zirconate titanate (PZT) coatings for Micro Electro Mechanical Systems (MEMS) devices. However, these devices require not only ceramic layer but also metal conductive layers. In this study, copper coating was fabricated by aerosol deposition process and evaluated the coating properties. Especially, the influence of process gas pressure was investigated. Average particle size of 1.5 μm of pure copper was deposited onto alumina substrate. The results show that increasing of process gas pressure increased both particle velocity and deposition efficiency. Furthermore, dense microstructure and lower electrical resistivity were obtained in the case of higher process gas pressure condition. However, excessive gas pressure caused peeling off the coatings due to residual stress in the coatings. The gas pressure for fabrication of copper coatings was optimized as 0.2 MPa in this study.
Palladium doped tungsten oxide thin films were prepared by RF reactive sputtering in a mixture of argon and oxygen at room temperature. XRD patterns indicated that these films were amorphous. SEM imaging indicated a smaller grain size of palladium doped thin film compared with that of undoped tungsten oxide thin film. With electrochromism, palladium doped tungsten oxide exhibited a reverse optical modulation with respect to the applied potential.
Ultra-thin Ga2O3 doped zinc oxide transparent conduction films was deposited on glass substrates using pulsed laser deposition method by ArF excimer laser (λ=193 nm) at the substrate temperature from 180 to 260 °C. The film thickness was changed from 40 to 110 nm-thick. The target containing 3 and 5 wt.% Ga2O3 were employed. As a result, resistivity of 2.69×10−4 Ω·cm was obtained for the film with 40 nm-thick fabricated using the target containing 5 wt.% Ga2O3 at substrate temperature of 260°C.
Gallium-doped zinc oxide (GZO) thin films have been deposited on Cyclo-Olefin Polymer (COP) substrates at room temperature by pulsed laser deposition (PLD) using FHG of Nd: YAG laser (λ=266 nm, 1.6 mJ/cm2) and then, thin films were annealed by pulsed laser with FHG of Nd: YAG laser (λ=266 nm, 8~20 mJ/cm2) at room temperature. As a result, the resistivity was improved from 6.61×10−4 Ω·cm to 5.94×10−4 Ω·cm for films annealed at a laser energy density of 12 mJ/cm2.
In this study, the mechanism of oxidation on silver-coated quartz crystal was investigated from the standpoint of future application to active oxygen monitoring under ultraviolet lamp processing. The effect of excited atomic oxygen (O (1D)) on the silver surface was monitored in real time utilizing the quartz crystal microbalance (QCM) method. To clarify the surface oxidation behavior on silver thin film, scanning transmission electron microscopy (STEM) and X-ray photoelectron spectroscopy (XPS) analyses were also performed. The results showed that the oxidation layer had a Ag2O structure and that the oxidation process progressed in three steps while the lamp was on.
Deep investigations were performed for further understanding of the nanostructure of sputtered WO3 films. The as-deposited films consisted of fine crystallites of several nm. As the pressure increased, the film density decreased and the surface area increased owing to open pores between grains. When films were annealed at 400°C or above, they were well crystallized to form monoclinic and randomly-shaped grains. Upon this crystallization, the film shrank and its density increased slightly, while the relative surface area substantially decreased.
Thin film single chamber solid oxide fuel cell (SC-SOFC) with Barium Cerium Oxide (BaCeO3) electrolyte film as proton conductor, grown by the helicon plasma sputtering, was studied to determine the power generation property at lower operating temperatures between 200 and 400°C in the gas mixtures of hydrogen and oxygen. An SC-SOFC with a BaCeO3 electrolyte film thickness of 5 μm could be operated at 400°C in the gas mixtures of hydrogen and oxygen and had a maximum open circuit voltage of 455 mV. However, a V-I property at 400°C of SC-SOFC was considerably poor as a development index of SOFC, because the cell resistance with a several kΩ was due mainly to the interface reaction resistance of between the Pt catalytic electrodes and an amorphous electrolyte film.
Fabrication of Flexible Transparent Resistive Random Access Memory (FT-ReRAM) which consists of Ga-doped ZnO (GZO) film not only as a memory layer but also as electrodes on the large Poly Ethylene Naphthalate (PEN) sheet was attained by introducing RF plasma assist DC magnetron sputtering method. The averaged transmittance in the visible region (400-800 nm) was 72%. The resistance change effect without morphological change was confirmed by using conducting atomic force microscope (C-AFM). Stable and repeatable bi-polar resistive switching by applying the voltage less than 2.5 V was confirmed in the all-GZO-FT-ReRAM. The present work showed the high applicability of the all-GZO-FT-ReRAM to achieve flexible transparent devices for the next generation.
Flexible transparent Resistive Random Access Memory (FT-ReRAM) consisting of Ga-doped ZnO (GZO) film not only as a memory layer but also as electrodes on the large PEN sheet were fabricated. The dependence of memory effect on the atmosphere during the memory layer sputtering was investigated. Resistive switching effect of the memory layer was investigated by directly applying voltage using conducting-AFM. Both memory layers deposited in H2 atmosphere, GZO(H2), and that in O2 atmosphere, GZO(O2), showed bipolar resistive switching with the same bias polarity dependence. I-V measurement for GZO(H2) showed that the relationship between applied bias polarity and consequent resistive change was the same as the result of C-AFM measurement. However, in GZO(O2), the bias polarity dependence observed in I-V measurement was opposite to that observed in C-AFM measurement. This result suggests that the atmosphere during the memory layer deposition affects the bias polarity dependence of bipolar resistive switching even in the ReRAM which has symmetrical structure.
Generally, a resistance change effect in transition metal oxides appear after the forming process. Here, a conducting filamentary path in which resistive switching occurs is formed in the forming process. However, there are resistive random access memory devices which do not need the forming process. These devices are initially in the low resistance state and start with a reset process, where reset means the switching from a low resistance state to a high resistance state. In these devices, the filaments are considered to be formed already in an initial state and, therefore, we call this kind of filaments “native filaments (NFIs)”. The initial resistance of devices containing NFIs and the probability that NFI is observed in as-prepared devices, PNFI, as a function of the device area were measured. As a result, it was suggested that NFIs exist in a certain averaged interval around the electrode. On the other hand, the memory layer thickness dependence of PNFI suggests that NFI consists of metal or oxygen vacancies which connect top and bottom electrodes. These vacancies are considered to be introduced during the reactive ion etching process of the top electrode and the memory layer fabrication.
NiO films were deposited by DC magnetron sputtering under various pressures from 0.12 to 12 Pa. The structure of the films was investigated using X-ray diffraction, scanning electron microscopy, and measurement of density and surface area. The films generally consisted of columnar grains. In the as-deposited films, as the pressure increased, voids developed between columnar grains and the density decreased with an abrupt increase in surface area. The surface area of a film with a low density considerably decreased after annealing at 400°C. The sensitivity of annealed films to NO2 at a concentration of 1 ppm in dry air was also investigated. The highest sensitivity, 3.0, was obtained at 200°C for the sensor made of a film with the lowest density deposited at 12 Pa.
SiO2 film was made on Si(100) by two-step film growth process at 100°C to improve the interface properties. The first part of the process is the direct Si oxidation using UV-excited ozone (O(1D)), which is generated by the UV irradiation to high concentrated (>90%) ozone gas. In the second part, O(1D) and Hexamethyldisilazane chemical vopor deposition (CVD)(O(1D)-CVD) process is used. The SiO2 film thickness of the direct Si oxidation for 10 min. in the two-step SiO2 film was estimated to be about 3.2 nm from the etching rate in change a buffered HF solution. Interface trap density Dit of the two-step SiO2 film with direct Si oxidation of 10 min. is almost equal to that of Si direct oxidation film alone. This result indicates that two-step oxidation process can be applied for the practical fabrication.
We have successufully developed a localized plasma etching system for failure analyses in semiconductor devices. The plasma was excited by a capacitively coupled plasma technique using a quartz capillary tube and the system can be operated by both methods of drawing etching gases into the glass tube (inward plasma method) and blowing etching gases out of the tube (outward plasma method). By the former method, we can reduce unfavorable materials leaving behind on the processed surface after processing. This successuful operation is comfirmed by the exposure of wires in 45 nm pattern rule device semiconductor.
Poly(3-octylthiophene)/Polymethylmethacrylate (P3OT/PMMA) composite waveguides were prepared by spin coating method as composing a prism-coupling waveguide. The UV-vis spectrum of P3OT/PMMA thin film was recorded in the range 300-900 nm using spectrophotometer to determine the optical absorption property of the composite thin film. The prepared P3OT/PMMA waveguide was treated with organic gas for 25 hrs to smoothing the surface of the thin film. An Nd: YAG laser with a wavelength of 1064 nm, a pulse width of 5 ns and a repetition frequency of 10 Hz was used for optical bistability measurement. The optical bistable characteristics of prism coupling waveguide comprising with P3OT/PMMA composite thin film was measured for different laser power intensities using optical bistable measuring equipment. The measured optical bistability displaced good stability and hysteresis characteristics. The input power dependence of optical bistability was observed and the switching on-off position shifted with the increase of input power intensity. In addition, the effects of organic gas treatment on the optical bistability of P3OT/PMMA composite waveguides were analyzed.