摘要:

Helium‐neon laser beam deflection is used to study excimer laser ablation of polymers and a YBa2Cu3O7−xsuperconductor. Density gradients above pulsed laser heated or ablated samples deflect the He‐Ne laser beam and this is measured using a position sensitive detector. The technique permits the determination of the laser fluence threshold for ablation both in a vacuum and in air, and the velocity of the ablation products in a vacuum. A model of the thermal deflection at low fluence was developed which enables measurements of thermal diffusivity of the air.

ISSN:0003-6951    

DOI:10.1063/1.102293

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Superconducting Y‐Ba‐Cu‐O (YBCO) films have been prepared byexsituO2annealing of multilayer films deposited on yttria‐stabilized zirconia substrates by sequential rf diode sputtering of Y2O3, BaF2, and CuO targets, all of which are chemically stable. If sputtering is performed in an Ar ambient, the as‐deposited films contain sufficient F to require its removal by annealing in wet O2at about 800 °C or above before the superconducting YBCO phase can be formed by annealing in dry O2. However, sputtering in an Ar‐O2ambient greatly reduces the F content, making it possible to obtain the superconducting phase by annealing in dry O2only. If the ambient contains about 20% O2, films withTc(R=0)>85 K can be prepared without wet‐O2annealing. The Ar‐O2process therefore has the potential forinsitupreparation of superconducting YBCO films.

ISSN:0003-6951    

DOI:10.1063/1.102294

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Bi2Sr2Ca1Cu2O8+x/Ag wires have been produced by using the ‘‘powder in tube’’ method and an appropriate annealing procedure. At 77 K these wires yield critical current densities up to 1.2×103A/cm2in zero magnetic field. Using ac susceptibility measurements it is shown that flux creep is limiting the critical current density at temperatures above ∼20 K. At lower temperatures flux creep becomes insignificant. At 4.2 K critical current densities up to 5.5×104A/cm2in zero magnetic field and up to 1.5×104A/cm2in a field of 26 T could be achieved, rendering possible the use of this material for very high field application.

ISSN:0003-6951    

DOI:10.1063/1.102295

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

We propose an antenna‐coupled microbolometer based on the resistive transition of a highTcsuperconducting film as a detector for far infrared and millimeter waves. Such microbolometers can be mechanically stronger, more easily fabricated, and much faster than conventional bolometric infrared detectors. A design analysis shows that a noise equivalent power of 2.5×10−12W Hz−1/2is achievable for modulation frequencies up to 10 kHz. The superconducting film must be of high quality with narrow resistive transition and low 1/f  noise.

ISSN:0003-6951    

DOI:10.1063/1.101998

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The synthesis of the superconducting YBa2Cu3O7−xfrom a soluble, molecular precursor with the composition Cu3O3Ba2Y(meOEt)7(meOEt is 2‐methoxyethoxide) is described. The precursor was synthesized from the reaction of a soluble copper (II) oxide polymer with alkoxides of barium and yttrium. Pyrolysis and oxidation of the precursor resulted in the formation of oriented sheets of the orthorhombic YBa2Cu3O7−xphase. The orientation in the bulk YBa2Cu3O7−xis believed to result from the presence of linear Cu‐O‐Cu‐O chains in the precursor. Bulk YBa2Cu3O7−x, prepared from the precursor, had an onset transition temperature of 92.5 K and zero resistance at 89.5 K.

ISSN:0003-6951    

DOI:10.1063/1.102296

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

YBa2Cu3O7−&dgr;thin films were deposited onto (100) SrTiO3substrates using 1064, 532, 355, 248, and 193 nm laser ablation. Transport measurements show lower normal‐state resistivities and higher critical currents in films deposited by the shorter wavelength lasers. The surface morphology of the films was rough with large particulates when the 1064 nm laser was used whereas much smoother surfaces with fewer and smaller particulates were obtained with the UV lasers. It is suggested that the better film quality obtained when the UV lasers are used is due to a small absorption depth of the UV photons in the ceramic target and to higher absorption by the ablated fragments. This leads to smaller ablated species and further fragmentation in the hotter plume and, therefore, to smoother and denser films.

ISSN:0003-6951    

DOI:10.1063/1.101999

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Analytic properties of scattering amplitudes are used to develop Breit–Wigner parametrizations of resonant tunneling currents in heterostructures. The analysis reveals a problem in using conventional Breit–Wigner resonance expressions to describe the important regions of peak current and negative differential resistance which occur when resonances are near the emitter threshold. Commonly used Breit–Wigner expressions (a) do not incorporate the correct threshold branch points, (b) do not possess the correct limit at threshold, and (c) do not satisfy unitarity both above and below threshold. Expressions which avoid such difficulties are deduced and used to parametrize tunneling current formulas.

ISSN:0003-6951    

DOI:10.1063/1.102000

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

High‐resolution scanning transmission electron microscope (STEM) images in the annular dark field (ADF) imaging mode approaching the theoretical point‐to‐point resolution limit are presented. The ADF images were obtained from a highTcsuperconducting YBa2Cu3O7−xthin‐film specimen at 100 kV. The 1.9 A˚ resolution lattice image, which is the smallest lattice spacing in the specimen, corresponds to the minimum resolvable spatial frequency with 5% contrast in the contrast transfer function for annular dark field, and is smaller than the resolution limit given by the Rayleigh criterion. This demonstrates that STEM ADF imaging can have a resolution approximately 40% better than that of the bright field conventional transmission electron microscope (CTEM) imaging at Scherzer condition.

ISSN:0003-6951    

DOI:10.1063/1.102297

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

Thin‐film fabrication techniques for forming three‐dimensional ‘‘point contacts’’ are presented. As‐fabricated nanobridges can be modified using electromigration to make the constriction region smaller or dirtier. Scientific applications to quantum transport studies, 1/fnoise, and electromigration are discussed.

ISSN:0003-6951    

DOI:10.1063/1.102001

出版商:AIP    

年代:1989

数据来源: AIP