Masahiro Iyori

Characteristics of Au/Ba/sub 1-x/K/sub x/BiO/sub 3//SrTiO/sub 3/(Nb) superconducting-base transistor

An Au/natural-barrier Ba/sub 1-x/K/sub x/BiO/sub 3/ (BKBO)/niobium-doped SrTiO/sub 3/ superconducting-base three-terminal device has been fabricated and tested. BKBO thin film was sputtered to create a base layer on the

Preparation of BaBiO3 thin films using an oxygen radical beam source

Abstract Films of BaBiO 3 (BBO), which is the matrix of the Ba 1− x K x BiO 3 (BKBO) superconductor, have been grown by molecular beam epitaxy (MBE) using an oxygen radical beam source. Crystallization of BBO films with (110) orientation was successfully confirmed at the low temperature of 300°C. According to the characterization for BBO films by X-ray photoelectron spectroscopy (XPS), in spite of the BBO thin film being synthesized at room temperature (RT), the film had the bismuth chemical state which is proper for both BBO and BKBO. This result indicates that the oxygen radical beam source is a useful activated oxygen source for the deposition of superconducting oxide films.

Preparation and characteristics of Ba1-xKx BiO3 superconductors using the plasma-arc melting and rapid quenching method

Abstract High-density, homogeneous Ba1-x K x BiO3 superconductors with relative density of 97% were successfully synthesized by the plasma-arc melting and rapid-quenching (PMQ) method. X-ray powder diffraction data showed a single Ba0.6K0.4BiO x structure with a lattice constant of a = 4.283 a. A sharp superconducting transition was observed at 28.5 K, with a transition width of less than 0.5 K.

Preparation and Characterization of a Superconductor-Semiconductor Junction: Ba1-xKxBiO3/Nb-Doped SrTiO3

Electrical properties of Au/native-barrier/BKBO tunnel junction and BKBO/SrTiO3:Nb(0.1wt%) heterojunction were studied. The differential conductance dI/dV spectrum of the Au/native-barrier/BKBO tunnel junction had a clear gap structure and was very close to the ideal BCS form with Δ(0)=3.2 meV. BKBO/SrTiO3:Nb heterojunction fabricated at 350°C showed tunneling-like I-V characteristics. In the dI/dV spectrum of the high-Tc superconductor/semiconductor junction, we observed a superconducting gap structure for the first time.

Epitaxial growth of Ba1−xKxBiO3 thin films by rf-magnetron sputtering

Abstract As-grown Ba 1−x K x BiO 3 (BKBO) epitaxial thin films with a critical temperature of 16.3 K have been successfully prepared at 300°C on SrTiO 3 (110) substrates by a high-pressure rf-magnetron sputtering. A preferred orientation of (110) and epitaxial growth of the BKBO film on the substrates were confirmed by X-ray diffraction (XRD) and reflection high-energy electron diffraction (RHEED), respectively.

Growth and Characterization of BaBiO3 Films by Molecular Beam Epitaxy

The fabrication and characterization of BaBiO3(BBO), which is the mother material of the Ba1-xKxBiO3 superconductor have been successfully performed. BBO films have been grown by molecular beam epitaxy (MBE) using an oxygen radical beam source at the lower pressure of 2.0×10−7 Torr. The BBO films were considered to be sufficiently oxidized from the Bi(4f) core level spectra estimated by X-ray photoelectron spectroscopy (XPS). These results demonstrate that the oxygen radical is effective for the formation of BBO films.

Photoemission Study of Superconducting Ba 0.6 K 0.4 BiO 3

Photoelectron spectra of a [110]-oriented epitaxial thin film of Ba0.6K0.4BiO3 have been studied by use of the synchrotron radiation to elucidate its electronic structure. Observed spectra shows a clear Fermi edge and agree with published band calculations. A normal emission study for the (110) surface shows a band crossing the Fermi level between the M and Γ points, which is assigned to the Bi-O sp orbital.

Characterization of BaBiO3 Thin Films Prepared by the MBE Method

BaBiO3 (BBO) thin films were synthesized onto SrTiO3(110) substrates by the molecular beam epitaxy (MBE) method using an oxygen radical source in order to oxidize the films. The oxygen radical source was operated at an rf power of 600 W. The background pressure during the deposition was 5xl0-5 Torr. X-ray photoelectron spectroscopy (XPS) of film prepared at room temperature (R.T.) showed that the chemical state of bismuth atoms in the film could be explained by multiple-valence states. This result suggests that the oxygen radical is effective for the formation of BBO films.

Fabrication and Properties of a Low-Leakage Au/MgO/Ba1-xKxBiO3 Tunnel Junction

A low-leakage tunnel junction of Au/Mg0/Ba1-xKxBi03(BKB0) has been successfully obtained using an artificial MgO barrier. BKBO surfaces were characterized by X-ray photoelectron spectroscopy (XPS) in order to determine the surface cleaning conditions for BKBO films. MgO films were fabricated on BKBO epitaxial films using the MBE method. The barrier heights at the BKBO side and Au side were estimated to be 200 meV and 600 meV by fitting the I- V characteristics assuming a barrier thickness of 35 A. The leak current of the tunnel junctions at zero-bias voltage was confirmed to be less than 1/3 of that using natural barriers.

Fabrication and Properties of MgO/Ba1−xKxBiO3Heteroepitaxial Structure

The fabrication and properties of MgO/Ba1−xKxBiO3 multilayered structures have been studied as a step toward all high-T c SIS junctions. Au/MgO/Ba1−xKxBiO3 tunnel-type junctions have been successfully fabricated using crystalline MgO film. MgO nlms were fabricated on BKBO epitaxial films using the MBE method. Junctions with polycrystalline MgO films show ideal BCS gap structure, whose Δ=3.6 meV. Moreover, epitaxial MgO films have been grown on BKBO films for the first time. These results demonstrate the possibility of realizing all high-T c SIS junctions consisting of BKBO/MgO/BKBO.