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The authors describe the designs of and report experimental results for one- and two-element high-T/sub c/ superconducting small antennas composed of self-resonant helical radiators and quarter-wave matching circuits. A 500-MHz-band antenna using a lambda /40 ( lambda is the free-space wavelength) radiator fabricated with Bi(Pb)SrCaCuO bulk realized a gain of -1.2 dBi, which indicates that this antenna achieves a high frequency of 70%. A 900-MHz-band two-element array antenna using lambda /20 radiator with a lambda /11 element spacing was designed to obtain a superdirective radiation pattern. The array antenna thus fabricated with YBaCuO bulk realized both a higher efficiency than a Cu antenna and a unidirectional radiation pattern. Furthermore, by adopting EuBaCuO thin-film meander lines as the matching circuit, the total length could be reduced to about 1/4 that of an antenna using a linear circuit. >

The surface characterization of a-axis EuBa/sub 2/Cu/sub 3/O/sub 7-y/ (EBCO) films sputtered onto SrTiO/sub 3/

X-ray photoemission results for interfaces prepared by cluster assembly with nanometer-size clusters deposited on high-{ital T}{sub {ital c}} superconductors (HTS's) show a reduction in reactivity because atom interactions with the surface are replaced by cluster interactions. Results for conventional atom deposition show the formation of overlayer oxides that are related to oxygen depletion and disruption of the near-surface region of the HTS's. For cluster assembly of Cr and Cu, there is a very thin reacted region on single-crystal Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}. Reduced reactivity is observed for Cr cluster deposition on single-crystal YBa{sub 2}Cu{sub 3}O{sub 7}-based interfaces. There is no evidence of chemical modification of the surface for Ge and Au cluster assembly on Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}(100). The overlayer grown by Au cluster assembly on Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} covers the surface at low temperature but roughening occurs upon warming to 300 K. Scanning-tunneling-microscopy results for the Au(cluster)/Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} system warmed to 300 K shows individual clusters that have coalesced into large clusters. These results offer insight into the role of surface energies and cluster interactions in determining the overlayer morphology. Transmission-electron-microscopy results for Cu cluster assembly on silica show isolated irregularly shapedmore » clusters that do not interact at low coverage. Sintering and labyrinth formation is observed at intermediate coverage and, ultimately, a continuous film is achieved at high coverage. Silica surface wetting by Cu clusters demonstrates that dispersive force are important for these small clusters.« less

Photoemission results demonstrate that atom deposition of Ti, Cr, and Cu at 20 K on the high‐temperature superconductors (HTSs) dramatically reduces interfacial reaction relative to 300 K growth but does not completely eliminate it. Thin Ti‐O or Cr‐O layers are formed during atom deposition of ∼2 A of Ti or Cr on YBa2Cu3O7 or Bi2Sr2Ca1Cu2O8 because oxygen is withdrawn from the Bi‐O and/or Cu‐O layers. Interfacial reactions are diffusion limited at 20 K, and metal overlayers nucleate on the reacted layers. These metal layers are more uniform than those grown at 300 K because clustering is suppressed. There is no additional disruption for Cr/HTS interfaces when warmed to 300 K, but increased disruption is evident for Ti/HTS interfaces. The differences reflect the stabilities of Cr and Ti in contact with their own interfacial oxide. Cu atom deposition on Bi2Sr2Ca1Cu208(100) at 20 K also leads to much less disruption than observed for deposition at 300 K.

X-ray photoemission results for Cr interaction on single-crystal Bi{sub 2}Sr{sub 2{minus}{ital x}}Ca{sub 1+{ital x}}Cu{sub 2}O{sub 8+{ital y}} demonstrate that interfaces nearly free of disruption can be formed by atom deposition at 20 K or by cluster assembly. For atom deposition at 20 K, a uniform metallic layer forms with only a slight reduction of Cu{sup 2+} bonding configurations, similar to that observed for nonreactive overlayers. This atom-assembled interface was stable when warmed to 300 K. Cluster assembly results in modification of the exposed Bi-O plane, but the Cu 2{ital p}{sub 3/2} emission shows no significant change because there was no change in Cu-O bonding. The irregular but complete layer of Cr on Bi{sub 2}Sr{sub 2{minus}{ital x}}Ca{sub 1+{ital x}}Cu{sub 2}O{sub 8+{ital y}} formed by cluster assembly exhibited limited reaction upon warming to 300 K. In contrast, interface formation at 300 K by atom deposition produced complete reduction of Cu{sup 2+}-like bonding within 30--50 A of the surface. These results demonstrate the competition between kinetic and thermodynamic processes.

An electron cyclotron resonance (ECR) ion beam has been utilized for a developing surface cleaning process of high‐Tc superconducting thin films. By means of silver‐contact resistivity measurements, and ex situ surface analysis using x‐ray photoelectron spectroscopy (XPS) and reflection high‐energy electron diffraction (RHEED), the effects of ECR treatment on an air‐exposed surface of a‐axis EuBa2Cu3O7−y (EBCO) films are examined. Ag/EBCO contacts are made with exposure of the EBCO surface to an ECR oxygen ion beam with ion current densities of 100 μA/cm2 at room temperature for about 30 min and the in situ deposition of silver. The contacts, which are not annealed in oxygen, exhibit low contact resistivity in the 10−8–10−7 Ω cm2 range. These values are about five orders of magnitude lower than those of samples fabricated without ECR treatment. Based on XPS and RHEED data, change in the EBCO surface caused by ECR treatment is surmised.

Photoemission studies of low‐temperature deposition of ∼30‐A‐diam Ge clusters on single‐crystal Bi2 Sr2−x Ca1+x Cu2 O8+y (100) show that an interface is produced with no evidence of substrate disruption. Analysis of the superconductor core level emission as a function of coverage indicates uniform overlayer growth and complete surface coverage. These cluster‐assembled interfaces were stable when warmed to 300 K, with only a slight reduction of Cu 2p3/2 satellite emission characteristic of the superconductor. In contrast, conventional atom‐by‐atom Ge deposition produces a Ge oxide layer and surface disruption.

Diffusion coefficients of sodium vapors in argon and helium gases were measured from 380 to 560°C by the Stefan method under atmospheric pressure. Careful considerations were made in the design of ...

Uniformity quantification of very thin PFPE (perfluoro-polyether) lubricant layers on thin film magnetic recording media is investigated using AR-ESCA. It is clarified that (1)of several non-uniform lube layer models, the ISLAND model ( with the lubricant coverage ratio on the SiO 2 top-layer surface defined as θ ) matches the experimental AR-ESCA data best. (2) Measured θ increases somewhat linearly with increases in lube layer average thickness, \bar{d} . (3)Coverage, θ, is closely related to media surface mechanical properties.