No abstract available

[en] We have developed ion-beam equipment which can produce metal ions in the energy range from very low energy (less than 10 eV) to high energy (400 keV). High-energy neutrals and secondary electrons which would be extremely harmful in low-energy experiments are removed from the beam. With this equipment, metallization of Si by low-energy ion beam deposition and by high-energy ion implantation has been performed. Film formation mechanisms and properties of deposited films were studied in the case of a low-energy Pd ion beam. The optimum ion energy, in terms of the collection efficiency and the condition of the film-substrate interface, was found to be 50-100 eV. Films with resistivity of the same order as that of the bulk material, and as thin as a few nanometers were obtained. It was confirmed by transmission electron microscopy that these films were already continuous and covered the entire substrate surface. In the case of metallization by high-energy ions, Pd, Ag, and Al ions were implanted into Si. It was found that a buried conductive layer is obtained only when concentration of implanted species exceeds a certain threshold. The buried PdSi layer formed by 320-keV Pd implantation at a dose level of 2.0 x 10¹⁷ cm^-2 had sheet resistance on the order of a few ohms and was stable under 800⁰C, 30 min anneal, Crystallinity of the implanted Si substrate surface was recovered after 600-800⁰C, 30 min anneal. (orig.)

[en] Epitaxial aluminium films were deposited onto clean Si(111) and Si(100) surfaces at room temperature by means of an ionized cluster beam (ICB). The effects caused by the kinetic energy and the electric charge of the ICB, such as enhancement of adatom migration and the formation of nucleation sites, resulted in epitaxial growth of thin films at low substrate temperatures. In this experiment the film formation process was observed using in situ Auger electron spectroscopy (AES) and reflection electron diffraction. These observations enabled the crystalline orientations and growth process features of the ICB aluminium films to be investigated. AES depth profiles, scanning ion micrographs, scanning electron micrographs etc. were obtained and were used to evaluate the properties of the deposited films and to elucidate the effects of acceleration of the ionized clusters. Alloy penetration of the films at the interface was not observed after annealing at 450⁰C. (Auth.)

[en] The breakdown of the diodes and the resistors in the back-diode circuit, which is a protection against damages of the klystron and other elements, was found at the pulse modulator No.2 after a series of operations since 1997. The breakdown of the resistor can be explained by assuming a preceding breakdown of the diodes possibly suffered an excessive surge voltage. However, there has been no problem found in the back-diode circuit at the pulse modulator No.1. As one of efforts made at LEBRA of Nihon University to reduce the fluctuation of the energy and the current of the beam in the linac, an optimum reservoir voltage of the thyratron in each modulator has been investigated in order to reduce the fluctuation of the modulator output voltage between successive pulses. (author)

[en] Film formation by the ionized cluster beam (ICB) method is studied from the standpoint of the effects of kinetic energy. First, the energy and the size of the vaporized-metal cluster are described. Then the effects of the kinetic energy of the ionized cluster on the initial stage of film formation and the resulting properties of the deposited films are discussed with microscopic and macroscopic observations. Specific differences between ICB deposition and mass-analysed ion beam deposition are also described. (Auth.)

No abstract available

[en] Oxides of chromium (Cr), molybdenum (Mo), or tungsten (W) were supported on mixed oxides of cerium and zirconium (CeO₂-ZrO₂) by an incipient wetness impregnation process, and used to investigate their activities for partial oxidation of methanol. High Resolusion Transmission Electron Microscope (HR-TEM) revealed that nanoparticles of Cr₂O₃, MoO₃ or WO₃ were formed on the CeO₂-ZrO₂ support. The particle sizes of Cr₂O₃, MoO₃ and WO₃ were 2-4, 3-6 and 4-5 nm, respectively. As a result of partial oxidation of methanol at 275 – 450 °C, formaldehyde (CH₂O) was obtained as the major product over all these catalysts. Cr₂O₃ supported on CeO₂-ZrO₂ produced both CO and CO₂ along with H₂ production, while MoO₃ and WO₃ on CeO₂-ZrO₂ support generated only CO as a by-product. It was found that MoO₃ supported on CeO₂-ZrO₂ showed the highest methanol conversion and CH₂O yield among these three catalysts. (paper)

[en] We investigate the hole transport in p-channel field-effect transistors doped with boron, at low temperatures (6-28 K). In transistors with a relatively large dimension, we observe the acceptor-mediated hopping and carrier freezeout, both of which are strongly influenced by the gate bias. In nanoscale transistors, these features turn into single-charge tunneling, i.e., the trapping/detrapping of single holes by/from individual acceptors. The statistics of the appearance of the modulation in a few ten samples indicates that the number of acceptors is small, or even just one, indicating that what we have observed is single-charge-transistor operation by a single-acceptor quantum dot