摘要:

We have observed an unusual hysteresis loop in rf power dependence of high‐temperature superconductor (HTS) coplanar transmission lines. At 77 K and 1 GHz, the signal transmission was linear (insertion loss <0.1 dB) until the input power (Pin) reached a critical value ofPc=0.4 W. An abrupt drop by ∼37 dB in the transmitted power (Pout) was observed atPin=Pcfollowed by a slow increase (Pout∝Pin0.62) forPin≳Pc. AsPmwas then decreased, it retraced the previous curve only untilPin=Pc. However, asPinwas reduced furtherPoutdid not rise untilPin=158 mW, at whichPoutstarted to increase rapidly and returned to the linear regime forPin<71 mW. Such a sharp transition and a strong hysteresis effect were unique to the HTS line whereas a gold line with an identical structure did not exhibit these characteristics. This behavior may be utilized for potential applications of new HTS microwave power (current) limiters and switches. Several possible origins for the hysteresis effect are proposed and discussed. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115112

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Ultrathin films of YBa2Cu3Oxwith good crystallinity and superconductivity were prepared by a modified off‐axis sputtering. The microstructure, with emphasis on surface morphology and formation of outgrowths, was studied by using atomic force microscopy and electron microscopy. It was found that many outgrowths were formed at the initial growing stage. Therefore it is important to suppress the nucleation of outgrowths at a very early growing step to obtain a smooth film. The nucleation of outgrowths is significantly influenced by surface defects on the substrate. Discussion is also made in correlation with the occurrence of an intermediate layer commonly observed onZrO2. From our observation, YBa2Cu3Oxmight be grown directly on the surface of ZrO2without forming any intermediate layer, if the film thickness is very small. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115113

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The epitaxial buffer system CeO2/YSZ was used to prepare YBCO films of high crystalline quality on silicon substrates by laser deposition. An advanced technique of step preparation in the YSZ buffer layer preserved the critical current densities ofjC(77 K)∼106A/cm2for 30 nm thick YBCO films also in the etched parts of the substrate. Further, a homogeneous growth over the 35 to 45 nm deep steps was observed. So we were able to realize step‐edge Josephson junctions with critical temperatures up to 77 K. Our dc SQUIDs on silicon substrates showed voltage modulation up to 74 K. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115114

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have used the recently established linear correlation between the total intensities of theL3,2‘‘white lines’’ in electron energy‐loss spectroscopy and the number of unoccupied 3dstates to probe the local electronic structure in epitaxially grown Co–Cr thin films. The significant enhancement of saturation magnetization measured for these epitaxial films, when compared to homogenized bulk alloys, has been correlated directly to the unoccupied 3dstates to the Co atoms in these materials. These measurements are the first direct electronic structure evidence that may support models associating the enhancement of saturation magnetization withintragranularsegregation in Co–Cr thin films. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115115

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Two all‐organic complexes, MC+TCNQ and BBDN+TCNQ, with electrical bistable states at room temperature have been discovered. The resistivity of these thin films prepared in vacuum can be transferred from high to low under a voltage of few volts. The transition time is <100 ns. Therefore, both materials are suitable for making write‐once read‐only memories. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115116

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Bright rings are observed in the scanning electron microscope (SEM) image when charge flashover in vacuum occurs on circularly bound polymethylmethacrylate surfaces using a SEM. The number and diameters of these rings vary with the applied observation voltage. These bright rings in the SEM correspond to the charge accumulation in the sample. The trapped charge transport in the insulator is either in the form of a large polaron or in the highly excited state. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115117

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report the fabrication and characterization of zinc‐indium‐oxide films with similar electrical conductivity and better transparency in both the visible and infrared compared with indium–tin–oxide, a widely used transparent conductor in many technological applications. Dramatically superior transmission properties in the 1–1.5 &mgr;m range in particular make zinc–indium–oxide attractive for use in infrared devices, where transparent electrodes are required. Resisitivities as low as 400 &mgr;&OHgr; cm result from doping with small quantities of Sn; Al, Ga, and Ge are also effective dopants. Deposition on glass and quartz substrates as amorphous films by pulsed laser deposition and dc reactive sputtering is described. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115118

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Wetting and adhesion should be treated as inherently irreversible processes, because, in the process of joining and separating two surfaces, available energy is dissipated. In a system that undergoes inherently irreversible processes, the second law of thermodynamics is always satisfied and can offer no information regarding the system’s equilibrium state. Therefore, to determine the equilibrium wetting angle, the law of energy conservation should be used. As a result, the advancing contact angle is found to be intrinsically higher than the receding one, regardless of the surface heterogeneity, and the extent of hysteresis is dependent on the amount of energy dissipated in the process of wetting and dewetting. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115119

出版商:AIP    

年代:1995

数据来源: AIP