Tsutomu Yotsuya

Effect of oxygen content on phonon Raman spectra of YBa2Cu3O7−δ

Abstract Raman spectra of YBa2Cu3O7−δ have been measured on samples with various oxygen content, which were obtained by quenching from various temperatures. It is found that the Raman band associated with oxygen vibrations observed at ∼ 500 cm−1 is very sensitive to the oxygen content; its frequency shifts continuously from 502 to 484 cm−1 as the quenching temperature is varied from below 500°C up to 1000°C. This result indicates that this band can be used to determine the oxygen content in YBa2Cu3O7−δ.

High-Energy Ion Beam Analysis of YBa2Cu3Ox Thin Films

The composition and crystalline structure of high-Tc superconducting YBa2Cu3Ox thin films formed on MgO(100) and Si(100) substrates have been investigated by Rutherford backscattering and channeling techniques. Y, Ba, Cu contents have been analyzed by employing a high-energy (over 4.5 MeV) 4He ions and large scattering angle (near 170°) condition, where Y, Ba and Cu peaks are clearly separated from each other. Oxygen concentration has been obtained through the use of low primary energy (below 2.5 MeV) and small scattering angle (below 150°) conditions, where the O peak is separated from the background. The crystalline quality of the films has also been investigated by ion channeling techniques.

INFRARED RADIATION DETECTOR WITH YBA2CU3OX THIN FILM

We investigated an infrared (IR) radiation detector using a c-axis oriented YBa2Cu3OX thin film with a microbridge structure. The photoresponse was measured under IR radiation and was found to depend on the bias current. A bolometric response was observed under relatively low bias current, which was inversely proportional to the square root of the modulation frequency of IR irradiation. The frequency dependence can be explained by a heat diffusion process that is similar to that of a microbolometer. With increasing bias current, a nonbolometric response was observed just above the superconducting transition temperature (Tc). This was caused by the enhancement of additional flux creep induced by modulated IR light, which was equivalent to an increase in resistance. The maximum responsivity and noise equivalent power (NEP) were 1.7×104 V/W and 2.1×10-14 W/Hz1/2, respectively.

Phonon Raman Scattering in Orthorhombic and Tetragonal YBa2Cu3O7-δ

Raman scattering spectra of orthorhombic and tetragonal YBa2Cu3O7-? have been measured. It is found that the Raman band associated with oxygen vibrations in the tetragonal phase is shifted to the lower frequency side with respect to the corresponding band in the orthorhombic phase. Seven Raman bands out of the ten theoretically predicted are found in the orthorhombic phase. No remarkable temperature dependence was observed for the phonon modes above 100 cm-1.

Pressure dependence of the electrical properties of TaN thin films

Abstract The pressure dependence of the electrical properties of TaN thin films was studied with a view to using the films for pressure measurement over a wide range. These films have properties that make them suitable for use as sensors in resistive thermoconductive vacuum gauges: a large effective heat-conducting area and a large temperature coefficient of resistance. The TaN thin films were deposited by reactive sputtering onto Corning 7059 glass. The sensor thus formed was found to be sensitive to pressure changes in the range 7 × 10 −5 −760 Torr . The sensitivity of the gauge increased with the resistance of the film and could be varied by changing the film dimensions even when the surface area was kept constant; it also increased with increasing surface area of the film.