Browsing by Author "HSU, HT"

Now showing 1 - 3 of 3

GROWTH PARAMETER EFFECT IN SUPERCONDUCTING YBA2CU4O8 THIN-FILMS BY DC MAGNETRON SPUTTERING
(1994-11-01)
WU, SC
;
HSU, HT
;
CHEN, FH
;
CHANG, WR
;
TSENG, TY
High-T-c YBa2Cu4O8 (124) thin films have been made by d.c. magnetron sputtering deposition on (100) MgO substrates. The effect of several processing variables, including the ratio of oxygen to argon, total pressure, and substrate temperature, on the superconducting properties of the thin films, were systematically investigated. The as-prepared films annealed in flowing oxygen at 800 degrees C for 4 h under ambient pressure obtained nearly phase-pure 124 and exhibited superconducting onset transition at 75 K.
PARAMAGNETIC MEISSNER EFFECT OF HIGH-TEMPERATURE GRANULAR SUPERCONDUCTORS - INTERPRETATION BY ANISOTROPIC AND ISOTROPIC MODELS
(1995-02-01)
CHEN, FH
;
HORNG, WC
;
HSU, HT
;
TSENG, TY
;
電子工程學系及電子研究所
The field-cooled magnetization of high-T-c superconducting ceramics measured in low magnetic fields exhibits the paramagnetic Meissner effect (PME), i.e., the diamagnetic signal initially increases with decrease in temperature but reaches a maximum at temperature T-d and later decreases with decrease in temperature. Even in some samples the signal is ultimately able to transform inversely into a paramagnetic regime once the sample is cooled below a temperature T-p as long as the applied field is sufficiently small. This PME has been observed in various high-T-c cuprates and is explained by disparate aspects. An anisotropic model, in which the granular superconductors are assumed to be ideally anisotropic, was first alternatively proposed in the present work so as to theoretically account for this effect. On the other hand, an isotropic model, suitable for granular superconductors with randomly oriented grains, was proposed to deal with the samples prepared by a conventional solid-state reaction method. The anomalous magnetization behavior in the present model was demonstrated to be the superposition of the diamagnetic signal, which occurs as a result of the intragranular shielding currents, over the paramagnetic one due to the induction of the intergranular component induced by these currents where the intergranular one behaved as the efective pinning centers. The PME was demonstrated by this model to exist parasitically in granular superconductors. This intergranular effect is therefore worthy of remark when evaluating the volume fraction of superconductivity for the samples from the Meissner signal, in particular, at a low magnetic field.
PRESSURE EFFECT ON YBA2CU3O7 THIN-FILM GROWTH IN OFF-AXIS RADIO-FREQUENCY MAGNETRON SPUTTERING
(1995-09-01)
WU, SC
;
TSAI, WC
;
HUANG, CK
;
HSU, HT
;
HUANG, CJ
YBa2CU3O7-x (123) thin films were fabricated on (100) MgO substrates by off-axis single target radio frequency (rf) magnetron sputtering. Our study focused on the effect of chamber pressure on the composition, microstructure, and superconductive properties on transition behavior and T-c, of the grown him studied. An empirical formula was derived to explain the dependence of the deposition rate of various components on the pressure. Next, we compared the transport mechanism of the sputtered particles between the off-axis rf and the on-axis direct current sputtering and determined the processing conditions that result in superconducting films of better quality. According to our findings, growth at higher pressures (>100 mTorr) produces more homogeneous and higher T-c superconducting films. (C) 1995 American Vacuum Society.