Takehiko Makita

Rubidium beam flux dependence of film properties of Ba1-xRbxBiO3 deposited by molecular-beam epitaxy using distilled ozone

We have focused our attention on the dependence of Ba1−xRbxBiO3 (BRBO) film composition ratio and film properties on rubidium‐beam‐flux intensity. BRBO films were deposited on MgO(100) substrates by molecular‐beam epitaxy (MBE) using distilled ozone. Systematic measurements showed that the rubidium content was nearly independent of rubidium‐beam‐flux intensity in a wide beam‐flux range. Therefore, it can be concluded that some degree of self‐control of rubidium stoichiometry is actually possible in BRBO film growth by MBE. This study also revealed that the BRBO film properties had strong dependences on rubidium‐beam‐flux intensity even in the range for self‐control of rubudium stoichiometry. Our study also clarified that rubidium‐beam flux affects the barium content in the BRBO film.

Fabrication and Electrical Properties of In/(Ba,Rb)BiO 3 /SrTiO 3 Three Terminal Device

In order to improve the device structure from the standpoint of determining more clearly current path and each junction area, we have fabricated In/(Ba,Rb)BiO3/SrTiO3(Nb) three terminal device using BaBiO3 thin film as an insulator between (Ba,Rb)BiO3 thin film and SrTiO3(Nb) substrate. (Ba,Rb)BiO3 and BaBiO3 thin films were prepared by molecular beam epitaxy method using distilled ozone. Quality of (Ba,Rb)BiO3 on BaBiO3 thin film was good as a result of X-ray diffraction measurement. The most favorable etching method for BaBiO3 thin film was wet etching using HCl. We have measured electrical properties and clarified electrical path of the three terminal device with improved structure. In the case of base common, current flowed through (Ba,Rb)BiO3 base under In deposit area.

Surface Resistances of BRBO Superconducting Thin Films

Measurements of microwave surface resistances of BaxRb1-xBi03 superconducting thin films grown by MBE are reported. Superconducting disk and rectangular planar resonators were fabricated and the relation between surface resistances and resonance Q value was analyzed by solving electric-magnetic field distribution in the BRBO superconducting films. The load Q value of the BRBO/Pb resonator was over 9000 and the surface resistances of 7.1 × 10−4Ω at the frequency of 19 GHz was obtained.

Initial Crystal Growth Stage of BRBO Thin Film

Thin film growth of BaBiO3 (BBO) on SrTiO3(100) and SrTi03(l10) substrates by molecular beam epitaxy was studied precisely. We prepared the BBO thin film of ~500A with surface roughness of ~30A. Surface roughness of the BBO thin film was systematically measured with the atomic force microscope. The crystal orientation and the surface roughness of the BBO thin films strongly depend on Ba-beam-flux intensity and on the orientation of the substrate.

Ultrathin film deposition of Ba1−xRbxBiO3 by molecular beam epitaxy using distilled ozone

A Ba1−xRbxBiO3 (BRBO) ultrathin film (120 A) with a zero‐resistance transition temperature of 14 K was deposited on a SrTiO3(110) substrate by molecular beam epitaxy using distilled ozone. The critical current density of 2×105 A/cm2 was achieved in 200‐A‐thick BRBO thin film, and this observed critical current density is much larger than the previously reported data. The dependence of BRBO film properties on film thickness is studied for the first time.