Hideki Takauchi

XPS Study on the Formation Process of the High-Tc Phase in the Bi-Pb-Sr-Ca-Cu-O System

X-ray photoemission spectroscopy (XPS) measurements were carried out to investigate the changes in the Cu ion valency through the formation of the high-Tc phase in the Bi-Pb-Sr-Ca-Cu-O superconducting system. The Cu2+ composition increased rapidly in the initial stages of sintering and became saturated, whereas the Cu+ and Cu3+ compositions showed a systematic change, within a certain sintering time, dependent on the sintering temperature. It was found that these changes in the Cu ion valency reflect the structural change in the formation of the high-Tc phase in this system.

Growth of Epitaxial CeO2 Films on (1012) Sapphire by Halide Source Plasma Enhanced Chemical Vapor Deposition.

We grew epitaxial CeO2 films on (012) sapphire by halide source plasma enhanced chemical vapor deposition (halide-PECVD) using CeBr3 and O2 as source materials. We obtained amorphous films at substrate temperatures of 620° C, polycrystalline films at 680° C, and highly aligned films at 720°C. X-ray diffraction patterns show that (001) CeO2 is parallel to (012) sapphire, and electron channeling patterns show [110] CeO2 aligned with [201] sapphire. AFM shows very smooth films with a maximum variation of ± 2 nm. We grew YBCO film on CeO2/sapphire with a T c of 83 K.

XPS measurements in Bi2Sr2Ca1−xYxCu2O8+d

We performed X-ray photoemission spectroscopy (XPS) measurements in Bi 2 Sr 2 Ca 1−x Y x Cu 2 O 8+d system in order to investigate the relation between the Cu valence and superconductivity. The negative chemical shift of the Cu 2p spectra indicated that holes in the Cu site decreased with increasing Y concentration. The change in the shape and the positive chemical shift of the O 1s spectra indicated that holes on the oxygen site in Cu-O layer increased with increasing Y concentration. The superconducting transition temperature decreased monotonically with decreasing the Cu valence and vanished when the Cu valence became less than 2.

Improved Emitter-Base Junction with In2O3 in Dielectric-Base Transistor

We studied In2O3 for use as an intermediate layer between the YBCO emitter electrode and the SrTiO3 base region of dielectric-base transistors (DBT). We fabricated and tested a YBCO(001)/In2O3(100)/SrTiO3(110) hetero-structure by using a laser-ablation deposition technique with high-density targets. Our YBCO/In2O3/n-SrTiO3 diode structure showed a current density that was one order of magnitude larger than with an MgO intermediate layer.