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The microwave electric field at breakdown for argon gas in a microgap (generally, gap size <1 mm) over a wide range of pressures and gap sizes was found to exhibit two behavioral pressure regimes. A high microwave electric field was established in the gap of a re-entrant mode resonator. By slowly raising the microwave electric field level, a breakdown level is reached where impact ionization induces low pressure argon gas to breakdown preferentially outside of the gap. At high pressure, breakdown is found to occur preferentially inside the gap, but only after the pressure is high enough for impact ionization to produce breakdown there. Impact ionization has a lower threshold electric field than the boundary-controlled processes, such as secondary electron emission, that would eventually produce breakdown inside the microgap if impact ionization did not occur first. Thus, the lower pressure regime is characterized by breakdown outside of the gap, while in the high-pressure regime, breakdown occurs inside the gap, in both cases by impact ionization. The transition pressure PT between these two pressure regimes depends on the gap size dgap, roughly as PT ∝ dgap−2. Consistent with the model developed here, this corresponds to the full-amplitude of electron oscillation in the gap field being commensurate with the gap size. [ABSTRACT FROM AUTHOR]

Presents information on a study which examined the surface impedance of bulk and thick film granular high temperature superconductors. Analysis of the weakly coupled grain model; Methodology of the study; Results and discussion.

The paper reports the fabrication of Zn-doped TiO nanotubes (Zn-TONT)/ZnO nanoflakes heterostructure for the first time, which shows improved performance as a photoanode in dye-sensitized solar cell (DSSC). The layered structure of this novel nanoporous structure has been analyzed unambiguously by Rutherford backscattering spectroscopy, scanning electron microscopy, and X-ray diffractometer. The cell using the heterostructure as photoanode manifests an enhancement of about an order in the magnitude of the short circuit current and a seven-fold increase in efficiency, over pure TiO photoanodes. Characterizations further reveal that the Zn-TONT is preferentially oriented in [001] direction and there is a Ti metal-depleted interface layer which leads to better band alignment in DSSC. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

This is the first report on the detailed study on low temperature (6–300 K) electrical conductivity and Seebeck coefficient on copper indium oxide polycrystalline thin films deposited on soda lime glass substrates by a reactive evaporation method. These films, characterized using various experimental techniques, show the highest electrical conductivity (20 to 125 S cm−1) reported to date as well as n- and p- type conductivity. The electrical conductivity mechanisms, based on Mott's, Seto's and Arrhenius models, in different temperature regimes, comprise of variable range hopping, grain boundary effect and activated thermal conduction. Most interestingly, the thin films manifest a high thermoelectric power factor and absorption in the UV region, indicating their potential in thermoelectric and UV energy conversion device fabrication, respectively. [ABSTRACT FROM AUTHOR]

Three-tone intermodulation distortion (IMD) was used to measure the even and odd order microwave nonlinearity of superconducting Tl2Ba2CaCu2O8 and YBa2Cu3O7 resonators. By using an off-resonance probe signal, the IMD generation is stimulated locally in the vicinity of the probe. Both 2nd and 3rd order IMD appear at the microwave resonant frequency, providing a synchronous comparison of the local even and odd order nonlinearities and a quantitative determination of the current densities that produce the intermodulation distortion. Comparison of synchronous 2nd and 3rd order IMD provides a characterization of the extent of time reversal symmetry breaking (TRSB) in the superconductor. As the probe is scanned across the resonator, the degree of TRSB is seen to vary in different regions, always exhibiting a significant rise in the 3rd order IMD at the critical temperature, Tc, consistent with expectation from the nonlinear Meissner effect. The ratio of 2nd order to 3rd order IMD current drops significantly at Tc, indicating a reduction in TRSB at the phase transition. [ABSTRACT FROM AUTHOR]

A method has been developed that uses three input tones to measure both even and odd order intermodulation distortions (IMDs) inside the pass band of resonant devices. With this technique the surface current density of both the driving signal and the IMD tones can be quantified. Synchronous, or same frequency, measurement of both even and odd order distortions permits quantitative comparison of the respective nonlinearity currents measured within the same time scale. As an example of this technique, a superconducting resonator is used to generate even and odd order IMDs at the same frequency, resulting in physical conclusions, which are pertinent to current research in high temperature superconductors. While varying the level of only one tone, the expected slope of the IMD current versus the driving signal current for both orders is unity, but that is only observed at high temperature when the superconductor becomes very lossy. An observed smaller slope at lower temperatures gives support to the linear-nonlinear interaction model. Also, a sharp increase in the third order IMD relative to the second order IMD near TC gives support to a substantial nonlinear Meissner effect. [ABSTRACT FROM AUTHOR]

Dispersion in periodic microstrip transmission lines was investigated by using S-parameters to calculate the characteristic impedance and the complex propagation constant. Dispersion curves determined from a variety of methods, including simulation with IE3D and measurement with a network analyzer, were compared with an analytic transcendental model providing self-consistent validation of each method. Simulated S-parameters agreed with measurement, including the case of a multi-layered substrate. Very similar dispersion curves were produced using simulated S-parameters, simulated current distributions, analytic calculation and measured S-parameters. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1010–1013, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24268 [ABSTRACT FROM AUTHOR]

For 10 years, thick-film YBCO has been used to make radio frequency filters out of three-dimensional superconductor coated structures. These filters are presented in a detail never before revealed. The chronology of solving technical problems such as coating and construction will be recounted from a historical perspective. The most recent design, which results in a 16-pole, 1.9 GHz filter in a housing measuring 145 mm×60 mm×35 mm, will be shown in detail. We will discuss the challenges in resonator design, substrate fabrication, coating technology, filter design, and filter realization associated with this filter. This overview demonstrates the progression of size over the past decade, resulting in an order of magnitude reduction in filter size and lessening size as a concern for system application of thick-film HTS filters. The impact of this size reduction on performance metrics such as Q and realizable filter order, as well as device characteristics such as intermodulation distortion, will be shown. [ABSTRACT FROM AUTHOR]

Many assessments of soil C have been restricted to the <2-mm fraction, but C has recently been identified in >2-mm fractions of forest mineral soils. Our objective was to determine the importance of the >2-mm fraction to whole-soil C pools in Pacific Northwest old-growth coniferous forests. Seventy-nine pedons in 18 western Washington and Oregon forests were sampled to a depth of 100 cm. The <2-mm fraction was separated from the >2-mm fraction by airdrying, physically crushing soil, and sieving; C was determined by Leco combustion. The >2-mm fraction contained up to 46% of the whole-soil C and averaged 23% for the seven forests that had C in that fraction. Following treatment with sodium hexametaphosphate to disaggregate soil material, up to 20% of whole-soil C remained in the >2-mm fraction. Thus, the >2-mm fraction C appears to be in stable and unstable aggregates, as well as concretions. The whole-soil C in the surface 100 cm of mineral soil ranged from 30 to 400 Mg C ha-1. Multiple regression analysis indicated this C pool was positively related to available water capacity, annual precipitation, and coarse woody debris (r² = 0.63 to 0.66, n = 18 forests). Similar results were obtained with only the <2-mm soil C, which is the basis of previous regional evaluations. This suggests consideration of the >2-mm fraction does not alter our understanding of the importance of climate and soil texture as controls of soil C pools, but it does affect the quantification of soil C pools in many old-growth forests in the Pacific Northwest. [ABSTRACT FROM AUTHOR]

We report our recent efforts in designs of several RF and microwave devices using high temperature superconducting (HTS) thin film technology. Devices considered include transmission lines, resonators, switches, and phase shifters in microstrip, stripline and coplanar waveguide. The circuit design, modeling, simulation, fabrication, packaging, and testing are discussed. Using a two-dimensional (2-D) EM simulator, we have optimized the geometry of the RF microstrip and stripline resonators for frequencies near 900 MHz. An unloaded Q is obtained as high as 80,000, three orders of magnitude greater than the traditional 2-D gold or copper resonators with identical structures. On-wafer probe and bit-error rate measurements show that the HTS transmission lines have an extremely small insertion loss and dispersion; thus they are ideal candidates for applications in multichip module interconnects and delay lines. A sharp switching characteristic and an unusually strong RF power hysteresis loop have been observed in the HTS lines. This interesting behavior has been utilized for designs of new HTS microwave phase shifters. The use of HTS lines can substantially reduce the losses suffered by conventional PIN diode switches. [ABSTRACT FROM AUTHOR]

The pressure dependence of the breakdown of nitrogen gas by a microwave field in microgaps down to 13 μm has been measured. Fits to a phenomenological function suggest that microwave breakdown in small gaps requires a higher collision frequency, νc. If the effective electric field on an electron in a microgap is interpreted as [formula] and then as the gap size is reduced, we find that the collision frequency needed to produce a minimum breakdown electric field shifts from νc = ω for large gaps to νc = 2ω for small gaps. [ABSTRACT FROM AUTHOR]

Micro-channels of nanosized columnar tracks were planted by heavy-ion irradiation into superconducting microwave microstrip resonators that were patterned from YBa2Cu3O7 − x thin films on LaAlO3 substrates. Three different ion fluences were used, producing different column densities, with each fluence having a successively greater impact on the microwave nonlinearity of the device, as compared to a control sample. Photoresponse (PR) images made with a 638 nm rastered laser beam revealed that the channel is a location of enhanced PR and a hot spot for the generation of intermodulation distortion. The microwave PR technique was also advanced in this work by investigating the role of coupling strength on the distribution of PR between inductive and resistive components. [ABSTRACT FROM AUTHOR]