Electrical characterization of poly(amide-imide) for application in organic field effect devices

The admittance spectra and current–voltage (I–V) characteristics are reported of metal–insulator–metal (MIM) and metal–insulator–semiconductor (MIS) capacitors employing cross-linked poly(amide–imide) (c-PAI) as the insulator and poly(3-hexylthiophene) (P3HT) as the active semiconductor. The capacitance of the MIM devices are constant in the frequency range from 10 Hz to 100 kHz, with tan δ values as low as 7 × 10⁻³ over most of the range. Except at the lowest voltages, the I–V characteristics are well-described by the Schottky equation for thermal emission of electrons from the electrodes into the insulator. The admittance spectra of the MIS devices displayed a classic Maxwell–Wagner frequency response from which the transverse bulk hole mobility was estimated to be ∼2 × 10⁻⁵ cm² V⁻¹s⁻¹ or ∼5 × 10⁻⁸ cm² V⁻¹s⁻¹ depending on whether or not the surface of the insulator had been treated with hexamethyldisilazane (HMDS) prior to deposition of the P3HT. From the maximum loss observed in admittance-voltage plots, the interface trap density was estimated to be ∼5 × 10¹⁰ cm⁻² eV⁻¹ or ∼9 × 10¹⁰ cm⁻² eV⁻¹ again depending whether or not the insulator was treated with HMDS. We conclude, therefore, that HMDS plays a useful role in promoting order in the P3HT film as well as reducing the density of interface trap states. Although interposing the P3HT layer between the insulator and the gold electrode degrades the insulating properties of the c-PAI, nevertheless, they remain sufficiently good for use in organic electronic devices.     

Parallel in-core and out-of-core solution of electrically large problems using the RWG basis functions

Currently, the problem size that can be solved in reasonable time using the Method of Moments is limited by the amount of memory installed in the computer. This paper offers a new development that not only breaks this memory constraint, but also maintains the efficiency of running the problem in-core. In this paper, highly efficient parallel matrix-filling schemes are presented for parallel in-core and parallel out-of-core integral-equation solvers with subdomain RWG basis functions. The parallel methodology for matrix filling is quite different when using a subdomain basis as opposed to using a higher-order basis. The parallel in-core solver uses memory, which is often expensive and limited in size. The parallel out-of-core solver is introduced to extend the capability of MoM to solve larger problems that can be as large as the amount of storage on the hard disk. Numerical results on several typical computer platforms show that the parallel matrix-filling schemes and matrix-equation solvers introduced here are highly efficient and achieve theoretical predictions. The implementation of these advancements with the widely used RWG basis functions creates a powerful tool for efficient computational electromagnetics solution of complex real-world problems.     

The Story of Collective Action: The Emergence of Ideological Leaders,Collective Action Network Leaders,and Cross-Sector Network Partners in Civil Society

Collective action and community ecology theories frame this study of longitudinal interorganizational networks in Croatia during the country's political transition. As time progresses toward political stability, grass-roots organizing activities shift through participation in new networks. Although engaged cross-sector communication was important in early stages of the transformation, homophilous partnering emerged as the system stabilized. System stability left room for organizations to exit the collective action network but with costs associated with centralized organizing. Over time, organizations embodied roles as ideological leaders, collective action network leaders, and within-sector network partners. We offer a unique contribution to community ecology and collective action theories with a communication-centered framework that emphasizes the nature of communication in interorganizational networks over a 4-year period.     

A new high performance phase shifter using BaxSr1-xTiO3 thin films

In this paper, a new device topology has been proposed to implement parallel plate capacitors using Ba_xSr_1-xTiO₃ (BST) thin films. The device layout utilizes a single parallel capacitor and minimizes conductor losses in the base electrode. The new design simplifies the monolithic process and overcomes the problems associated with electrode patterning. An X-band 180° phase shifter has been implemented using the new device design. The circuit provided 240° phase shift with an insertion loss of only 3 dB at 10 GHz at room temperature. We have shown a figure of merit 93°/dB at 6.3 GHz and 87°/dB at 8.5 GHz. To our knowledge, these are the best figure of merit results reported in the literature for distributed phase shifters implemented using BST films at room temperature     

795 nm and 1064 nm dual pump thulium-doped tellurite fibre for S-band amplification

Gain measurement in thulium-doped tellurite fibre is demonstrated with a maximum internal gain of 7 dB at 1480 nm. An improvement in gain by a factor of 2 is achieved using a 795 nm and 1064 nm dual pump scheme. Gain in tellurite fibres extends to longer wavelength than in fluorides, showing improved overlap with the C-band EDFA.     

Vapor Annealing as a Post-Processing Technique to Control Carrier Concentrations of Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> Thin Films

This article demonstrates that carrier concentrations in bismuth telluride films can be controlled through annealing in controlled vapor pressures of tellurium. For the bismuth telluride source with a small excess of tellurium, all the films reached a steady state carrier concentration of 4 × 10¹⁹ carriers/cm³ with Seebeck coefficients of −170 μV K⁻¹. For temperatures below 300°C and for film thicknesses of 0.4 μm or less, the rate-limiting step in reaching a steady state for the carrier concentration appeared to be the mass transport of tellurium through the gas phase. At higher temperatures, with the resulting higher pressures of tellurium or for thicker films, it was expected that mass transport through the solid would become rate limiting. The mobility also changed with annealing, but at a rate different from that of the carrier concentration, perhaps as a consequence of the non-equilibrium concentration of defects trapped in the films studied by the low temperature synthesis approach.     

Public Relations: State of the Field

Public relations is both a professional practice and a subfield of communication with its own research and theory base. Public relations is relatively young as an academic field, however, having developed identifiable theory in only about the last 50 years. The field of public relations is developing into a theoretically based area of applied communication that has the potential to inform several areas of communication/mass communication and to offer theoretic and conceptual tools useful in health, risk, and political communication, among others. Because many readers are unfamiliar with public relations theory and research, this article first reviews and summarizes theory-related scholarship in public relations, then categorizes and explains the theoretic trends in the field. The article concludes by demonstrating how one of public relations' theoretic/conceptual tools, issues management, can apply across all areas of applied communication.     

Thermoelectric quantum-dot superlattices with high ZT

Following the experimentally observed Seebeck coefficient enhancement in PbTe quantum wells in Pb_1−xEu_xTe/PbTe multiple-quantum-well structures which indicated the potential usefulness of low dimensionality, we have investigated the thermoelectric properties of PbSe_xTe_1−x/PbTe quantum-dot superlattices for possible improved thermoelectric materials. We have again found enhancements in Seebeck coefficient and thermoelectric figure of merit (ZT) relative to bulk values, which occur through the various physics and materials science phenomena associated with the quantum-dot structures. To date, we have obtained estimated ZT values approximately double the best bulk PbTe values, with estimated ZT as high as about 0.9 at 300 K.     

Demonstration of multi-core photonic crystal fibre in an optical interconnect

A novel microstructured fibre has been created for use in an optical interconnection system. The fibre has low crosstalk with a high density of cores corresponding to 1150 channels/mm/sup 2/. A repeating pseudorandom binary sequence has been used to demonstrate a four-channel transmit/receive system using vertical cavity surface emitting lasers as both emitters and detectors.     

Extrusion of YAG Tubes Shows that Bottom‐up Processing is Not Always Optimal

Liquid‐feed flame spray pyrolysis provides easily dispersed, unaggregated nanopowders with average particle sizes of 20–70 nm depending on the processing conditions. Their chemical compositions can be controlled to ppm levels via control of the initial precursor solution. In this paper, Y₃Al₅O₁₂ composition nanopowders are produced that are atomically mixed but offer a hexagonal crystal structure rather than a YAG structure. Y₂O₃ and δ‐Al₂O₃ nanopowders are also produced and mixed to evaluate reactive sintering. It is shown that nanopowder/polymer mixtures permit the extrusion of tubes that retain their shape on debindering and sintering to ≥95% theoretical density. More importantly, the sintering behavior of hex‐Y₃Al₅O₁₂ is compared with that of tubes formed using 3:5 Y₂O₃:δ‐Al₂O₃ mixtures to test the so‐called bottom‐up paradigm, which suggests that mixing on the finest length scales should provide optimal control of sintering rates, final densities, and grain sizes. Instead, it is found that reactive sintering is faster and offers better control of final grain sizes. Dense sintered tubes are translucent, and dimensional uniformity is maintained from extrusion through sintering.