Fumihiko Toda

XPS Studies of 80 K-Phase Bi-Sr-Ca-Cu-O Single Crystals

The XPS (X-ray photoelectron spectroscopy) measurements of the 80 K-phase Bi-Sr-Ca-Cu-O single crystals were carried out on surfaces obtained by cleaving in vacuum, by cleaving in air and heating in vacuum, and by Ar+-sputter etching of the air-cleaved-and-heated surface. The chemical bond natures of all the constituent elements from the air-cleaved-and-heated surface are approximately equal to those from the vacuum-cleaved surface. Sr and Ca from the sputtered surface are more oxidized than those from the vacuum-cleaved surface.

In/(Ba, Rb)BiO3/SrTiO3(Nb) Three-Terminal Device

A superconductor-based three-terminal device of In/(Ba, Rb)BiO3/SrTiO3(Nb) structure was produced. The (Ba, Rb)BiO3/SrTiO3(Nb) interface is a Schottky junction with a barrier height of 1.8 eV, while the (Ba, Rb)BiO3/In interface is a junction with rectifying characteristics. The static properties of the three-terminal device as a transistor were determined in common-base and common-emitter configurations. With a base thickness of up to 50 nm, α=0.94 and β=10 were obtained, confirming that this device operated as a transistor.

Ba 1-x Rb x BiO y Thin Films Prepared by Rf Magnetron Sputtering

We prepared the Ba1-xRbxBiOy (BRBO) thin films on a MgO(100) substrate by rf magnetron sputtering method using a mixture gas of He and O2, and an off-axis geometry, where the substrate was located perpendicular to targets. From the results, we found that the BRBO films prepared using the targets of Ba:Rb:Bi=1:z:1 (z=0.5∼1.0) contained Ba, Rb, Bi and O, and that the films were dominantly (110)-oriented. In addition, the results of electron probe microanalysis indicates that the compositions of the BRBO films were dependent on Rb contents in the targets.

Ba0.6Rb0.4 BiO Thin Films by RF Magnetron Sputtering

We prepared the BaRbBiO(BRBO) thin films by rf magnetron sputtering using He+O2 gas(He=80%) at the substrate temperatures(Tsub) from room temperature(RT) to 450°C. The MgO(100) substrate was set at the position perpendicular to the target. From the results of X-ray photoelectron spectroscopy, we found that the BRBO films prepared at the Tsub from RT to 450°C contained Ba, Rb, Bi and O. In addition, X-ray diffraction results indicated that the films were (100) and (110)-oriented.

X-Ray Photoelectron Spectroscopy Study of Junction Interface in In/BaRbBiO Films

The In/BRBO/STO specimens were fabricated by depositing Ba0.6Rb0.4Bi1.0Oy (BRBO) on the SrTiO3 (STO) substrates by means of molecular beam epitaxy using 100% pure ozone and then, by depositing In metal. From the X-ray photoelectron spectroscopy results, we found that the In metal deposited on the BRBO/STO specimen removed the oxygen from BRBO and produced InOx layer at the interface between In metal and BRBO.

Electrical Properties of Al/Al2O3/(Ba, Rb)BiO3/SrTiO3(Nb) Three Terminal Device

A three terminal device with the Al/Al 2 O 3 /(Ba, Rb)BiO 3 /Nb-doped SrTiO 3 structure was fabricated using a superconducting base layer. The stable interface between (Ba, Rb)BiO 3 and the artificial oxide barrier was obtained using in situ AL 2 O 3 deposition. The output characteristics were measured as functions of input current. A current gain greater than 2 was obtained in the common emitter configuration.