[en] The new high temperature superconductors have triggered enormous interest not only because of the unique physics involved but also because of their technical potentials, such as the promise for propagation of extremely short electrical pulses. Superconducting band caps of --20TH_z are predicted assuming BCS theory for the superconductor, making lossless propagation of electrical pulses as short as 50 fs possible. Despite microwave measurements at low frequencies of several gigahertz first studies at higher frequencies by Dykaar et al have shown distortion-free propagation of 100-GHz electrical pulses on YBa₂Cu₃O₃ (YBCO) lines for --5-mm propagation distance. Results were also reported for aluminum coplanar lines and a YBCO ground plane. The authors report on the propagation of 1-ps electrical pulses (1-THz bandwidth) on YBCO coplanar transmission lines defined on lanthanum gallate (LaGaO₃) as a substrate. On LaGaO₃, YBCO grows highly oriented as on SrTiO₃. However, unlike SrTiO₃, LaGaO₃ has a much lower dielectric constant and small losses in the terahertz frequency range. Electrical pulses of --750-fs duration are generated in a radiation-damaged silicon-on-sapphire photoconductive switch integrated into a 20-μm coplanar stripline with 10-μm spacing and excited with 100-fs optical pulses from a CPM laser. An μ1-THz bandwidth electrical contact is made to the YBCO coplanar stripline defined on LaGaO₃ using a flip-chip geometry. They find that electrical pulses broaden only from 750 fs to 1 ps with little loss in amplitude on traveling through their flip-chip input and propagated electrical pulses are probed by electooptic sampling in two small LiTaO₃ crystals separated by 3 mm

[en] We have successfully made low resistance contacts between high-quality films of YBa₂Cu₃O_7-x (YBCO) and single-crystal Si substrates through Ag-Au interconnections. The YBCO films were deposited by laser ablation on an epitaxial yttria-stabilized zirconia buffer layer on Si and had zero-resistance critical temperatures of 83--85 K after patterning into lines. Specific contact resistivities (resistance-area products) of the YBCO to Si interconnection, limited by the Au to Si interface, of 10^-6 Ω cm² were achieved on heavily doped Si after deposition and patterning of the YBCO film. This demonstrates the use of high-temperature superconductors as a wiring layer compatible with conventional Si metal-oxide-semiconductor processing

[en] We study the propagation of terahertz bandwidth electrical pulses on high critical current density c-axis oriented YBa₂Cu₃O/sub 7-//sub δ/ (YBCO) coplanar transmission lines deposited epitaxially on the low dielectric loss substrate lanthanum aluminate (LaAlO₃). The losses on the YBCO transmission line are lower than on an equivalent gold line on the same substrate at temperatures below 50 K. At higher temperatures, absorption and dispersion of the ultrashort electrical pulses are observed in reasonable agreement with Mattis--Bardeen theory

[en] Catalyst-free GaN nanowires with InGaN quantum disks (QDs) were characterized by scanning/transmission electron microscopy (S/TEM) and photoluminescence. A variety of structures, from QDs with large strain fields to apparently strain free QDs were observed. TEM lattice imaging revealed dislocations in the QD regions of the samples. Stacking faults were also observed and appear to be associated with the GaN growth temperature rather than the presence of indium. Energy dispersive X-ray spectroscopy in the TEM revealed indium concentrated in stacking faults but not always localized in the QD regions. Photoluminescence spectra show a red-shift, possibly associated with indium concentration. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] This paper reports on the behavior of high-quality YBa₂Cu₃O_7-x (YBC) thin films with Ag over-layers. The authors chose to study Ag in detail because of its widespread use as contact metallization and the author's earlier studies of proximity effects in YBC. The details of transport critical current measurements are presented. The Ag coatings can reduce normal state resistance while not degrading the critical current density, J_c

[en] Several fully functional programmable voltage standard chips, each having a total of 32768 Nb endash PdAu endash Nb Josephson junctions, have been fabricated and tested. The chips are based on a new design that provides fast programmability (1 μs) between voltages and stable voltage operation from -1 to +1V. A comparison of the new standard with a conventional Josephson voltage standard is in agreement to 0.5±1.1 parts in 10⁹. We demonstrate the utility of this standard by measuring the linearity of a digital voltmeter. copyright 1997 American Institute of Physics

[en] A multiple technique approach is used to study YBa₂Cu₃O₇ grown on SrTiO₃ as a function of post-deposition annealing temperature. X-ray diffraction data are used to determine the relative amounts of a-axis and c-axis oriented growth. These results are compared to the surface morphology of the films observed by SEM. Secondary ion mass spectrometry (SIMS) is used to study the diffusion of substrate elements into the YBCO films as a function of post-deposition annealing temperature. The data obtained from all these techniques are correlated to determine an optimized temperature for post-deposition annealing. The results of this study show that the desired c-axis oriented growth can be obtained with minimal diffusion of substrate elements into the film at annealing temperatures of 750 degree C

[en] The development of thin-film dielectrics compatible with the epitaxial growth of YBa₂Cu₃O_7-δ (YBCO) is crucial to the fabrication of multilayer device and circuit structures. The authors of this paper investigate the YBCO/SrTiO₃ (STO) system by fabricating YBCO/STO bilayers and simple YBCO/STO/YBCO crossover structures. The thin films were deposited in situ by pulsed laser deposition and analyzed using x-ray diffraction and scanning electron microscopy. The film interfaces were characterized by secondary ion mass spectrometry (SIMS) depth profiling. The authors have developed photolithographic and wet-etching processes for patterning the crossovers which are compatible with these materials