Organophosphonate self-assembled monolayers for gate dielectric surface modification of pentacene-based organic thin-film transistors: a comparative study

Organic thin-film transistors using pentacene as the semiconductor were fabricated on silicon. A series of phosphonate-based self-assembled monolayers (SAMs) was used as a buffer between the silicon dioxide gate dielectric and the active pentacene channel region. Octadecylphosphonate, (quarterthiophene)phosphonate, and (9-anthracene)phosphonate SAMs were examined. Significant improvements in the sub-threshold slope and threshold voltage were observed for each SAM treatment as compared to control devices fabricated without the buffer. These improvements were related to structural motif relationships between the pentacene semiconductor and the SAM constituents. Measured transistor properties were consistent with a reduction in density of charge trapping states at the semiconductor-dielectric interface that was effected by introduction of the self-assembled monolayer.     

True Antecedents

In this note I discuss what seems to be a new kind of counterexample to Lewis’s account of counterfactuals. A coin is to be tossed twice. I bet on ‘Two heads’, and I win. Common sense says that (1) is false. But Lewis’s theory says that it is true. (1) If at least one head had come up, I would have won.

Assignment of congested NMR spectra: carbonyl backbone enrichment via the Entner-Doudoroff pathway

In NMR spectra of complex proteins, sparse isotope enrichment can be important, in that the removal of many (13)C-(13)C homonuclear J-couplings can narrow the lines and thereby facilitate the process of spectral assignment and structure elucidation. We present a simple scheme for selective yet extensive isotopic enrichment applicable for production of proteins in organisms utilizing the Entner-Doudoroff (ED) metabolic pathway. An enrichment scheme so derived is demonstrated in the context of a magic-angle spinning solid-state NMR (MAS SSNMR) study of Pf1 bacteriophage, the host of which is Pseudomonas aeruginosa, strain K (PAK), an organism that uses the ED pathway for glucose catabolism. The intact and infectious Pf1 phage in this study was produced by infected PAK cells grown on a minimal medium containing 1-(13)C d-glucose ((13)C in position 1) as the sole carbon source, as well as (15)NH(4)Cl as the only nitrogen source. The 37MDa Pf1 phage consists of about 93% major coat protein, 1% minor coat proteins, and 6% single-stranded, circular DNA. As a consequence of this composition and the enrichment scheme, the resonances in the MAS SSNMR spectra of the Pf1 sample were almost exclusively due to carbonyl carbons in the major coat protein. Moreover, 3D heteronuclear NCOCX correlation experiments also show that the amino acids leucine, serine, glycine, and tyrosine were not isotopically enriched in their carbonyl positions (although most other amino acids were), which is as expected based upon considerations of the ED metabolic pathway. 3D NCOCX NMR data and 2D (15)N-(15)N data provided strong verification of many previous assignments of (15)N amide and (13)C carbonyl shifts in this highly congested spectrum; both the semi-selective enrichment patterns and the narrowed linewidths allowed for greater certainty in the assignments as compared with use of uniformly enriched samples alone.     

Spatial cues alone produce inaccurate sound segregation: the effect of interaural time differences

To clarify the role of spatial cues in sound segregation, this study explored whether interaural time differences (ITDs) are sufficient to allow listeners to identify a novel sound source from a mixture of sources. Listeners heard mixtures of two synthetic sounds, a target and distractor, each of which possessed naturalistic spectrotemporal correlations but otherwise lacked strong grouping cues, and which contained either the same or different ITDs. When the task was to judge whether a probe sound matched a source in the preceding mixture, performance improved greatly when the same target was presented repeatedly across distinct distractors, consistent with previous results. In contrast, performance improved only slightly with ITD separation of target and distractor, even when spectrotemporal overlap between target and distractor was reduced. However, when subjects localized, rather than identified, the sources in the mixture, sources with different ITDs were reported as two sources at distinct and accurately identified locations. ITDs alone thus enable listeners to perceptually segregate mixtures of sources, but the perceived content of these sources is inaccurate when other segregation cues, such as harmonicity and common onsets and offsets, do not also promote proper source separation.     

Stable high-power TE01 gyro-TWT amplifiers

The stability of high power gyro-TWT amplifiers operating in the low-loss TE₀₁ mode of cylindrical waveguide has been studied, Linear theory has been used to determine the threshold start-oscillation beam current for absolute instability in the operating mode and the critical section lengths for the dominant gyro-BWO interactions occurring at various cyclotron harmonics in other waveguide modes. The performance of the amplifier was evaluated with a nonlinear, self-consistent slow-timescale simulation code. Utilizing interaction sections whose lengths are less than the threshold start-oscillation length and are separated by attenuating severs for isolation, two stable three-section devices have been designed which are predicted to yield: (1) a peak output power of 230 kW at 35 GHz with an efficiency of 23%, a saturated gain of 46 dB and a constant-drive bandwidth of 6% for a 100 kV, 10 A electron beam with an α=ν_⊥ /ν_z =1.0 and an axial velocity spread Δν_z/ν_z=5% and (2) 105 kW at 94 GHz with 21% efficiency, 45 dB saturated gain and 5% constant-drive bandwidth for a similar 5 A electron beam. In addition, the design of the 0 dB input/output couplers and the MIG electron gun are given. Due to the low loss of the TE₀₁ mode, both of these amplifiers can be operated continuously     

A new portable sound processor for the University of Melbourne/Nucleus Limited multielectrode cochlear implant.

A new processor, called the spectral maxima sound processor (SMSP), has been developed for the University of Melbourne/Nucleus Limited multielectrode cochlear implant. The SMSP analyses sound signals by means of a bandpass filterbank having 16 channels which are allocated tonotopically to the implanted electrodes. Every 4 ms, typically, the six channels with the largest amplitudes are selected, and six corresponding electrodes are activated. In an ongoing study the performance of the SMSP is being compared with that of the Mini Speech Processor (MSP). Some results of speech perception tests from the first two SMSP users are presented, in which scores for the recognition of vowels, consonants, and words all showed significant increases over the corresponding MSP scores.     

Operation of a large-orbit high-harmonic multicavity gyroklystronamplifier

An experimental four-cavity, fifth-harmonic gyroklystron is described that separates at 11.3 GHz in a 1.2-KG magnetic field. This device used longer drift regions than previous configurations. Principal results reported include 45 dB of small-signal gain and 0.6 kW of output power. Other results include the measurement of phase noise characteristics and the identification of spurious output signals. An improved beam diagnostic which determines the pitch of the electron orbits was used together with a fluorescent uranium-glass witness plate and beam-current diagnostics to characterize the electron beam. This information was used to perform analytic modelling and computer simulation of the amplifier. The experimental results are compared with the predictions of the analytic theory and simulation, and substantial agreement is demonstrated