Contact-induced crystallinity for high-performance soluble acene-based transistors and circuits

The use of organic materials presents a tremendous opportunity to significantly impact the functionality and pervasiveness of large-area electronics. Commercialization of this technology requires reduction in manufacturing costs by exploiting inexpensive low-temperature deposition and patterning techniques, which typically lead to lower device performance. We report a low-cost approach to control the microstructure of solution-cast acene-based organic thin films through modification of interfacial chemistry. Chemically and selectively tailoring the source/drain contact interface is a novel route to initiating the crystallization of soluble organic semiconductors, leading to the growth on opposing contacts of crystalline films that extend into the transistor channel. This selective crystallization enables us to fabricate high-performance organic thin-film transistors and circuits, and to deterministically study the influence of the microstructure on the device characteristics. By connecting device fabrication to molecular design, we demonstrate that rapid film processing under ambient room conditions and high performance are not mutually exclusive.     

Ionic effects on the equilibrium dynamics of DNA confined in nanoslits

The ionic effects on the dynamics and conformation of DNA in silt-like confinement are investigated. Confined lambda-DNA is considered as a model polyelectrolyte, and its longest relaxation time, diffusivity, and size are measured at a physiological ionic strength between 1.7-170 mM. DNA properties change drastically in response to the varying ionic environment, and these changes can be explained by blob theory with an electrostatically mediated effective diameter and persistence length. In the ionic range we investigate, the effective diameter of DNA that represents the electrostatic repulsion between remote segments is found to be the main driving force for the observed change in DNA properties. Our results are useful for understanding the manipulation of biomolecules in nanofluidic devices.     

Electron Pairing in Ferroelectric Niobium and Niobium Alloy Clusters

Cryogenic molecular beam experiments show that the ferroelectric dipole moments of small niobium clusters with an even number of valence electrons n are typically greater than those with odd n. This is verified in alloy clusters Nb _N X _M where X=Al, Au, O, Mn, Fe, and Co; N≤100;M≤3. Like in superconducting alloys, Mn doping quenches the effect while Al and Au enhance it, suggesting a relation between cluster ferroelectricity and bulk superconductivity. A correlated ground state is proposed where the even-odd effect is caused by the depolarizing effect of a single unpaired electron.     

Wrinkling and Edge Buckling in Orthotropic Sandwich Beams

A sandwich beam buckling problem is studied here using two-dimensional elasticity to model the beam constituents. The global and local instability of such a beam with orthotropic constituents under various boundary conditions are investigated. The face sheet and the core are assumed to be linear elastic orthotropic continua. General buckling deformation modes of the sandwich beam subjected to uniaxial compressive loading are considered. The appropriate incremental stress and conjugate incremental finite-strain measure for the instability problem of the sandwich beam, and the corresponding constitutive model are addressed. It is shown that a sandwich beam having a core with a negligible stiffness compared to the face sheets is prone to fail by edge buckling. The present analysis is compared with several previous analytical studies and corresponding experimental results. Finite-element analyses are carried out for comparison against the theoretical predictions. The formulation used in the finite-element code is discussed in relation to the formulation adopted in the theoretical derivation.     

A music-based HIV prevention intervention for urban adolescents.

Objective: This research examines the process of conducting and evaluating a music-based HIV prevention intervention among urban adolescents, and is informed by the information, motivation, behavioral skills (IMB) model. Design: Musically talented opinion leaders were recruited to write, record, and distribute HIV prevention themed music to their peers to increase HIV prevention motivation, behavioral skills, and behaviors. In this 3-month field experiment, participants were 306 students enrolled in health classes at each of three large multiracial urban high schools (one treatment school; two control schools). Main Outcome Measures: Measures of HIV prevention information, motivation, behavioral skills, and behaviors, both pre- and postintervention. Results and Conclusion: Results indicate that the intervention influenced several aspects of HIV prevention motivation, behavioral skills, and condom use and HIV testing behaviors. This research demonstrates that the incorporation of music into HIV prevention interventions for adolescents has the potential to be effective. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Vertical Phase Separation in Small Molecule:Polymer Blend Organic Thin Film Transistors Can Be Dynamically Controlled

Blending of small‐molecule organic semiconductors (OSCs) with amorphous polymers is known to yield high performance organic thin film transistors (OTFTs). Vertical stratification of the OSC and polymer binder into well‐defined layers is crucial in such systems and their vertical order determines whether the coating is compatible with a top and/or a bottom gate OTFT configuration. Here, we investigate the formation of blends prepared via spin‐coating in conditions which yield bilayer and trilayer stratifications. We use a combination of in situ experimental and computational tools to study the competing effects of formulation thermodynamics and process kinetics in mediating the final vertical stratification. It is shown that trilayer stratification (OSC/polymer/OSC) is the thermodynamically favored configuration and that formation of the buried OSC layer can be kinetically inhibited in certain conditions of spin‐coating, resulting in a bilayer stack instead. The analysis reveals here that preferential loss of the OSC, combined with early aggregation of the polymer phase due to rapid drying, inhibit the formation of the buried OSC layer. The fluid dynamics and drying kinetics are then moderated during spin‐coating to promote trilayer stratification with a high quality buried OSC layer which yields unusually high mobility >2 cm² V^?1 s^?1 in the bottom‐gate top‐contact configuration.     

Endothelial cell electrical impedance parameter artifacts produced by a gold electrode and phase sensitive detection

Frequency dependent cellular micro-impedance estimates obtained from a gold two-electrode configuration using phase sensitive detection have become increasingly used to evaluate cellular barrier model parameters. The results of this study show that cellular barrier function parameter estimates optimized using measurements obtained from this biosensor are highly susceptible to both time dependent and systematic instrumental artifacts. Based on a power spectral analysis of experimentally measured microelectrode voltages, synchronous, 60 Hz, and white Gaussian noise were identified as the most significant time dependent instrumental artifacts. The reduction of these artifacts using digital filtering produced a corresponding reduction in the optimized model parameter fluctuations. Using a series of instrumental circuit models, this study also shows that electrode impedance voltage divider effects and circuit capacitances can produce systematic deviations in cellular barrier function parameter estimates. Although the implementation of an active current source reduced the voltage divider effects, artifacts produced by coaxial cable and other circuit capacitive elements at frequencies exceeding 1 kHz still remained. Reducing time dependent instrumental fluctuations and systematic errors produced a significant reduction in cellular model barrier parameter errors and improved the model fit to experimental data.     

Differentiation of Aeromonas isolated from drinking water distribution systems using matrix-assisted laser desorption/ionization-mass spectrometry

The genus Aeromonas is one of several medically significant genera that have gained prominence due to their evolving taxonomy and controversial role in human diseases. In this study, matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) was used to analyze the whole cells of both reference strains and unknown Aeromonas isolates obtained from water distribution systems. A library of over 45 unique m/z signatures was created from 40 strains that are representative of the 17 recognized species of Aeromonas, as well as 3 reference strains from genus Vibrio and 2 reference strains from Plesiomonas shigelloides. The library was used to help speciate 52 isolates of Aeromonas. The environmental isolates were broken up into 2 blind studies. Group 1 contained isolates that had a recognizable phenotypic profile and group 2 contained isolates that had an atypical phenotypic profile. MALDI-MS analysis of the water isolates in group 1 matched the phenotypic identification in all cases. In group 2, the MALDI-MS-based determination confirmed the identity of 18 of the 27 isolates. These results demonstrate that MALDI-MS analysis can rapidly and accurately classify species of the genus Aeromonas, making it a powerful tool especially suited for environmental monitoring and detection of microbial hazards in drinking water.     

Double-codified gold nanolabels for enhanced immunoanalysis

A novel double-codified nanolabel (DC-AuNP) based on gold nanoparticle (AuNP) modified with anti-human IgG peroxidase (HRP)-conjugated antibody is reported. It represents a simple assay that allows enhanced spectrophotometric and electrochemical detection of antigen human IgG as a model protein. The method takes advantage of two properties of the DC-AuNP label: first, the HRP label activity toward the OPD chromogen that can be related to the analyte concentration and measured spectrophotometrically; second, the intrinsic electrochemical properties of the gold nanoparticle labels that being proportional to the protein concentration can be directly quantified by stripping voltammetry. Beside these two main direct determinations of human IgG, a secondary indirect detection was also applicable to this system, exploiting the high molar absorptivity of gold colloids, by which, the color intensity of their solution was proportional to the concentration of the antigen used in the assay. Paramagnetic beads were used as supporting material to immobilize the sandwich-type immunocomplexes resulting in incubation and washing times shorter than those typically needed in classical ELISA tests by means of a rapid magnetic separation of the unbound components. A built-in magnet graphite-epoxy-composite electrode allowed a sensibly enhanced adsorption and electrochemical quantification of the specifically captured AuNPs. The used DC-AuNP label showed an excellent specificity/selectivity, as a matter of fact using a different antigen (goat IgG) a minimal nonspecific electrochemical or spectrophotometric signal was measured. The detection limits for this novel double-codified nanoparticle-based assay were 52 and 260 pg of human IgG/mL for the spectrophotometric (HRP-based) and electrochemical (AuNP-based) detections, respectively, much lower than those typically achieved by ELISA tests. The developed label and method is versatile, offers enhanced performances, and can be easily extended to other protein detection schemes as well as in DNA analysis.