Kozo Obara

Resistance Anomaly of Nb–Si Thin Films

A resistance anomaly of very thin Nb–Si films is reported. The anomaly is characterized by a sudden drop in the resistance by a factor of ~103 at a temperature (TD) of ~180K without any application of pressure. The lower resistance-state (~zero Ω) is constant to 4.2K so far as we measured. TDdepends on measuring current and on magnetic fields. The anomaly has properties very similar to those of CuCl under high pressure.

Oxidation process of metastable super-fine niobium oxide particles

Abstract Metastable super-fine niobium oxide particles, which have a cubic crystal habit, were formed using a magnetron sputtering system. The growth kinetics of oxide formation at the surface of super-fine particles was investigated using the electrical resistance across the oxide layers. The time dependence of the resistance was measured at room temperature under a partial pressure of oxygen from 10-6 to 10 Torr and two pressure dependences were found: P1/2.1O2 and P1/4.0O2. These pressure dependences sh ow the formation of neutral and monovalent defect clusters due to oxygen interstitials.

Collision processes between sputtered particles on high speed rotating substrate and atomic mass dependence of sticking coefficient

Collision processes of incident particles at a substrate surface are important factors to decide the microscopic growth processes in vapor phase. Incident particles are classified into two groups: primary particles and secondary particles. In order to investigate the momentum dependence of collision processes in the practical growth conditions, an experimental method, which was used a rotating disk as a substrate, is presented. In this report, we present sticking probability of Zr, Nb and Ta on the surface covered with cobalt atoms. The sticking probabilities of primary particles decreased with increasing the atomic masses. On the other hand, those of secondary particles did not show clear atomic mass dependence except for the momentum dependence. Final composition of deposited particles was the sum of the contributions of primary particles and secondary particles, whose ratio depended on the width of the sector because the sticking probability of secondary particles was dominated by the collision with the primary argon atoms.

Deposition of superconducting (Cu, C)–Ba–O films by pulsed laser deposition at moderate temperature

Superconducting (Cu, C)?Ba?O thin films have been epitaxially grown on (100) SrTiO3 at a low growth temperature of 500?600??C by pulsed laser deposition. The dependences of their crystallinity and transport properties on preparation conditions have been investigated in order to clarify the dominant parameters for carbon incorporation and the emergence of superconductivity. It has been revealed that the CO3 content in the films increases with increasing both the parameters of partial pressure of CO2 during film growth and those of growth rate and enhancement of superconducting properties. The present study has also revealed that the structural and superconducting properties of the (Cu, C)?Ba?O films are seriously deteriorated by the irradiation of energetic particles during deposition. Suppression of the radiation damage is another key for a high and uniform superconducting transition. By these optimizations, a superconducting onset temperature above 50?K and a zero-resistance temperature above 40?K have been realized.

Formation of metastable niobium oxide by the vapor quenching of sputtered particles

Abstract Metastable niobium oxides, which have bcc structure and ∼ 55 at.% oxygen, were found. These materials were produced by a new sputtering system, in which four improvements were made. The condensation processes of sputtered particles in the gas phase and on the substrate were investigated, and it was found that a pressure of 0.25 Torr is critical for the formation of metastable niobium oxide superfine particles. Agglomerations of these metastable materials were decomposed to NbO with vacancies ordered fcc structure and to a new type NbO2 after annealing at 700°C for 45 min. Unique relations were found between lattice constants of these three materials.

A New Approach for Sustainable Energy Systems due to the Excitation of Inner‐core Electrons on Zinc Atoms Induced by Surface‐ion‐recombination

The crisis of Nuclear power plants due to the March 11, 2011 Tsunami in Japan suggests an increased need for sustainable science and technology in our society. The authors propose a new physical approach with surface‐ion‐recombination (SIR) due to the inner‐core excitation of zinc atom [Ne]3s23p63d104s2 that brings no magnetic moment. Condensed material indicated the energy dependence of X‐ray diffraction intensity, in which exists strong diffuse scattering intensities at 10 eV, 90 eV, 100 eV and 230 eV. These energies are strictly corresponding to zinc of electron systems (3s,3p,3d and these combination). Our approach may have the potential of techniques for future nanotechnology, especially for hydrogen storage systems.

Photoemission study of (Cu,Tl)-1223 and Tl-1223 with T/sub c/ above 130 K

A change of electronic structure and chemical bond nature of high pressure synthesized (Cu,Tl)Ba/sub 2/Ca/sub 2/Cu/sub 3/O/sub 9-/spl delta// [(Cu,Tl)-1223] and TlBa/sub 2/Ca/sub 2/Cu/sub 3/O/sub 9-/spl delta// [Tl-1223] with reduction-annealing, which leads to a significant rise of their superconducting transition temperature T/sub c/ above 130 K, has been investigated by in-situ photoemission spectroscopy. Their intrinsic surface nature has been achieved by fracturing in vacuum. In (Cu,Tl)-1223, a Fermi edge is observed for the first time. Trivalent Tl and heavily over-doped states of Cu-O clusters are dominant in as-grown specimens of both systems. The annealing resulted in remarkable shifts of photoemission spectra of Ba and Tl core levels towards higher binding energy with an increase of the annealing temperature, which means a selective oxygen-depletion around their charge-reservoirs and a decrease of valency of Tl. In contrast, there are quite little shape-changes and movements in valence band spectra and core signals of Cu and O. These results reveal that, in the high temperature-treated specimens, major portions of the electrons left should be absorbed into the cations in their charge reservoir, which consequently should cause a much more moderate change of the hole-concentration of the CuO/sub 2/ planes. It suggests that the utilization of this charge-redistribution mechanism in over-doped specimens should be an advantageous way to optimize the electronic structure of the 1223 phases for high T/sub c/.

Surface Electronic States of Adsorbed Nitrogen Molecules on Oxidized Nickel Surface

We present a new technique to investigate the electronic surface structures of metal electrodes and experimental data on oxidized surfaces of nickel electrodes. The experimental system consists of a simple triode structure and an electromagnet to control the momentum of incident electrons. The magnetic field dependence of the transmission electron current to the metal electrodes depends on the electron density at the electrode surface. When the electron density at the surface is high, the incident electrons are scattered by quantized surface states in the surface potential barrier. On the other hand, in the case of low electron density, the incident electrons show resonance characteristics due to the presence of discrete electronic states as a result of the generation of a periodic surface potential. Molecular nitrogen adsorption causes a change in the surface potential, and the bonding states intermediate between covalent bonds and van der Waals-like bonds are detected.

Slowly Relaxing Structural Defects of Zinc Films with Excited States Induced by Ion Recombination Processes

In this paper we present experimental results with the ion recombination process in the vapor phase growth method. We consider the growth process of only one element case, Zinc, because of the clarification of the change of electron states in the element, not the entropy effect due to different elements. The advantages of using the ion recombination process are the following; 1) controllability of total energy, 2) the highest quenching rate, 3) locality of the collision. The total energy of the ion system was below 240 eV. Zn- ions exist on the growth front surface and Zn+ ones impinge to the growth surface from the vapor phase. The crystal structures of deposited zinc films are measured with the XRD system. Very strong diffuse scattering intensity of x-ray diffraction was observed at 10 eV, 90 eV, 100 eV and 230 eV after seven months “annealing” in room temperature from the preparation. These experimental facts suggest the effectiveness of the application of the excitation process of the inner core electron system as a new advanced material process. In this process, the ion recombination process and the existence of a metastable state are essentially important factors.

Sticking probability of sputtered particles and collisions on rotating Ni–P substrates

We present a new method to arbitrarily control surface concentration from one alloyed target. Introduction of the high-speed movement of a substrate changed the primary sticking probability of sputtered particles and generated gas flow near surface. The induced momentum of argon atoms to the direction of the substrate increased the effective secondary sticking probability. The important factor to modify the surface concentration is the area of the sector, which controls the collision frequency near the surface.