岡井 大祐

A crystallization process in an amorphous state under isothermal condition is examined for binary alloys ZrNi and ZrNi2 by differential thermal analysis (DTA). Time dependence of DTA curves is measured at several constant temperatures just below crystallization temperature. The fraction of crystallized volume in amorphous state and its time evolution during isothermal annealing are measured. These data are analyzed by the Johnson-Mehl-Avrami formula. The Avrami exponent is 2.4 +/- 0.1 for ZrNi and 3 similar to 4 depending on the set temperature for ZrNi2. The activation energy for crystallization of amorphous ZrNi and ZrNi2 was estimated by plots of lnt(1/2) vs. 1/T.

We have examined the effect of the loss in the cavity on the measurement accuracy of surface resistance (Rs) of a superconducting thin film using a microstripline resonator. The Rs of a YBCO thin film was measured as a parameter of the height of the cavity's ceiling. The investigation revealed that the loss in the ceiling affected the measurement accuracy of Rs for a comparatively lower ceiling height. However, when the ceiling's height was sufficiently high, the effect was negligible.

The effects of the crystallinity and surface roughness of CeO2 buffer on R-plane Al2O3 substrate on the microwave surface resistance (R-s) of YBa2Cu3Oy (YBCO) thin alms are discussed. We estimated R-s from the transmission characteristics of the microstrip line resonator at 25 K and 6.7 GHz. X-ray diffraction (XRD) of theta-2 theta and phi-scan showed that CeO2 was completely (001)-oriented and in-plane aligned crystal. Fear CeO2 samples with different thicknesses were prepared using identical conditions except for the deposition time, The dependence of RI on CeO2 thickness was measured in the range from 10 mn to 200 nm. The value of R-s was minimum at CeO2 thickness of 100 ma The dependence of R-s vs CeOs thickness was similar to that of the amount of a-axis domains against the thickness The crystallinity of thin CeO2 was poor because the lattice was strongly strained by Al2O3. This affected the quality of the upper YBCO layer. In contrast, thick CeO2 had excellent crystallinity. However, for the thickness of more than 100 nm a drastic change in surface morphology was observed bg atomic force microscopy (AFM), a number of projections appeared on the CeO2 suface. These projections act as nucleation centers for the a-axis domains.

The effects of the crystallinity and surface roughness of CeO2 buffer on R-plane Al2O3 substrate on the microwave surface resistance (R-s) of YBa2Cu3Oy (YBCO) thin alms are discussed. We estimated R-s from the transmission characteristics of the microstrip line resonator at 25 K and 6.7 GHz. X-ray diffraction (XRD) of theta-2 theta and phi-scan showed that CeO2 was completely (001)-oriented and in-plane aligned crystal. Fear CeO2 samples with different thicknesses were prepared using identical conditions except for the deposition time, The dependence of RI on CeO2 thickness was measured in the range from 10 mn to 200 nm. The value of R-s was minimum at CeO2 thickness of 100 ma The dependence of R-s vs CeOs thickness was similar to that of the amount of a-axis domains against the thickness The crystallinity of thin CeO2 was poor because the lattice was strongly strained by Al2O3. This affected the quality of the upper YBCO layer. In contrast, thick CeO2 had excellent crystallinity. However, for the thickness of more than 100 nm a drastic change in surface morphology was observed bg atomic force microscopy (AFM), a number of projections appeared on the CeO2 suface. These projections act as nucleation centers for the a-axis domains.

超伝導薄膜の表面抵抗の測定のために, マイクロストリップ線路共振器(MSR)法が用いられている. 我々は,プローブ結合型MSR法検討している. この方法により, 薄膜に対して非接触で表面抵抗の測定ができる. 表面抵抗を正確に求めるためには, 高精度でQ値測定ができる技術が必要とされる. 本論文では, 測定精度に与えるキャビティの形状効果について報告する. 超伝導薄膜の表面抵抗を精度よく測定するためには, キャビティの天井とアンテナの位置が重要であることが明らかとなった.

マイクロストリップ線路共振器法は, 超伝導マイクロ波バッシブデバイスを設計する上で重要なパラメーターである、超伝導薄膜の表面抵抗、磁場侵入長、誘電体基板の比誘電率、誘電損の値を測定することができる。表面抵抗と磁場侵入長の正確な測定のためには、マイクロストリップ線路共振器法を系統的に検討する必要がある。我々は、表面抵抗と磁場侵入長の測定精度に与える膜厚効果を調べた。その結果、表面抵抗、磁場侵入長の正確な値を求めるためには、薄膜の膜厚を考慮する必要があることが分かった。また、マイクロストリップ線路共振器法によりYBCO薄膜の表面抵抗と磁場侵入長を測定した。表面抵抗は、3.9GHz、21Kで177.2μΩ、磁場侵入長λ(0)は、0.37μmと求めることができた。