摘要:

Low‐resistivity tin‐doped indium oxide thin films have been implanted with115In+ions in order to increase the concentration of electrically active oxygen vacancies. The carrier density, Hall mobility, and optical properties of the as‐implanted films have been determined as a function of In+dose. Three dose ranges are described. For doses up to 2.5×1014/cm, both carrier density and Hall mobility initially decrease to respective saturation values. Then, at doses between 2.5×1014/cm2and 2.5×1015/cm2, the carrier density increases while the mobility remains constant. At still higher doses, the Hall mobility begins to decrease abruptly. Mechanisms accounting for the implantation‐induced changes in each of these three dose ranges are discussed. In particular, it is shown that the rate of increase of the carrier density with In+dose in the intermediate range agrees quantitatively with the rate of production of oxygen‐vacancy donors that is necessary to fully accommodate the implanted In substitutionally on In2O3lattice sites during implantation. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359568

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A difference analysis method has been presented to separate and characterize interface and oxide traps generated in the metal–oxide–semiconductor structure under Fowler–Nordheim stress. The oxide trap relaxation measurement has been performed in dynamic voltage mode. For a high constant voltage stress condition, the effective oxide traps can be obtained by the difference Fowler–Nordheim current relaxation characteristics. For a low‐voltage condition, the interface and effective oxide traps can be separated and determined by the difference subthreshold voltage relaxation characteristics. Using combined difference Fowler–Nordheim current and subthreshold voltage measurements, the density, centroid, and generation/capture cross section of the oxide traps can be obtained without the double current–voltage technique, thus permitting more accurate and quick measurement of the generated oxide traps. All difference Fowler–Nordheim current and subthreshold voltage versus the electron‐fluence characteristics exhibit spectrum features. Analytical expressions for computing the interface and oxide traps have been derived and experimental results have been presented for a Fowler–Nordheim tunnel metal–oxide–semiconductor structure. Two interface and two oxide traps generated at Fowler–Nordheim stress have been obtained by the new technique. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358719

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A simple superconducting loop with a Josephson junction subject to a time‐sinusoidal magnetic flux embedded in a noise background is considered. Cooperative effects, arising from the interplay between the noise and modulation are described; they manifest themselves in the response, measured as an output signal‐to‐noise ratio. In particular, it is shown that the response displays the stochastic resonance effect, wherein the output signal‐to‐noise ratio passes through a maximum at a critical value of the noise strength. A simple theory, based on the characterization of the superconducting quantum interference device as a bistable switching element, is seen to yield good qualitative agreement with the experimental results. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358720

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A low voltage argon ion sputter technique was used to form grain boundary junctions in YBa2Cu3O7−xthin films on MgO. The YBa2Cu3O7−xthin film grown on a pre‐sputtered region of MgO was rotated 45° about the [001] axis relative to the YBa2Cu3O7−xthin film grown on an adjacent unsputtered region of the substrate. YBa2Cu3O7−xthin films were grown using pulsed organometallic beam epitaxy (POMBE). The current‐voltage and resistance‐temperature characteristics of individual grain boundary junctions demonstrated weak‐link‐type behavior. Sputter‐induced 45° grain boundary junctions are advantageous in device applications because they are planar and simple to form in many configurations. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358721

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

For 7,7,8,8‐tetracyanoquinodimethane (TCNQ)‐treated (Bi,Pb)2Sr2Ca2Cu3Oz[(Bi,Pb)‐2223] super‐ conductors, a superstructure which can be described as 2a0×2b0×c0has been observed by electron diffraction. Superconductivity is virtually destroyed in the TCNQ‐treated (Bi,Pb)‐2223 cuprate. Superconductivity (withTcup to 110 K) may be recovered for a TCNQ‐treated sample by being annealed in flowing oxygen gas. Then the 2a0×2b0×c0superstructure is found to disappear. This suggests that the superstructure may be caused by an ordering of oxygen vacancies. High resolution transmission electron microscopic observations reveal that the oxygen vacancies reside not only in the CuO2sheets, but also likely in the SrO sheets. A model for the superlattice in both CuO2−xand SrO1−ysheets is proposed. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358722

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The higher order zero field steps of long inline and overlap Josephson junctions have been investigated experimentally by means of low temperature scanning electron microscopy. The results indicate that several stable states are possible when more than one fluxon is present in the junction, corresponding to a different spacing among the fluxons during their propagation. These dynamic states should differ by the spectrum of the emitted radiation. Numerical simulations show that the fluxon interaction with plasma oscillations appears to be responsible for the observed behavior. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358723

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The inter‐ and intra‐grain critical current densities of melt processed YBa2Cu3O7−∂(YBCO) thick films have been measured as a function of temperature using vibrating sample magnetometry. The width of theM‐Hhysteresis curve has been observed to scale with the cube of the sample width for temperatures up to ∼70 K and applied fields of greater than 1 T which implies that current flows on the length scale of the sample over this temperature and field regime. An exponential decrease of magnetic moment hysteresis with temperature up to ∼70 K and between ∼80 K andTchas been observed and attributed to the dominance of inter‐ and intra‐granular current, respectively. An empirical model is presented to account for the observed dependence of the critical current density on temperature, based upon weak link behavior within the ‘‘Hub and Spoke’’ like morphology characteristic of melt processed YBCO thick films. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358724

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have measured the magnetoresistance curves of a silver‐clad Bi (2223) tape below critical temperatureTcover a magnetic field range up to 8 T. At temperatures well belowTcthe magnetoresistive transition can be well described by a thermally activated flux flow (TAFF) process. The activation energies inferred from such dissipation measurements are found to have the formU=U0+U’(H,T), whereU0is magnetic field and temperature independent,U’(H,T) is proportional to (1−T/Tc)n/H. At temperatures very close toTcthe TAFF dissipation can no longer be found and the magnetoresistance seems to be determined by the combination of viscous flux flow and thermal fluctuation. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358725

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The analytical magnetization versus time expressions for several flux‐pinning models for high‐Tcsuperconductors are deduced. Magnetic relaxation and hysteresis studies have been performed on a zone‐melted YBa2Cu3O6+xsample by SQUID. Nonlogarithmic magnetization decay is observed at relatively high temperatures; we attribute this to the nonlinearU(J) relationship which may arise from the local pinning potentialUp(x), rather than collective pinning. At 70 K, the experimental data fits extremely well to the expressionM(t)=M0+a(T)ln ln(t/&tgr;) which is the result of the exponentialU(J) relationship. Based on thisU(J) law, the local pinning potential is determined to beUp(x)=U0(x/x0)[1−ln (x/x0)]. The voltage–currentE(J) resulting from the observedU(J) relationship, as well as the role of the Y2BaCuO5(211) phase in zone‐melted YBCO is discussed. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.358726

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An energetic model of statistic domain behavior is applied on the magnetization process of grain oriented FeSi‐steel sheets. The physical constants of the model are derived from anisotropic energy contributions, initial susceptibility, coercivity, and saturation magnetization. Calculated in the [100], [011], and [111] – directions, the hysteretic magnetization curves indicate good agreement with measurements from the demagnetized state up to saturation. The better correspondence between theory and experiments at weak fields is achieved by using realistic initial occupation probabilities for the domain structure. This assumption leads to complex mutual dependencies of the statistic domain’s volume fractions, which have not been considered in previous works. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358727

出版商:AIP    

年代:1995

数据来源: AIP