Electronic Excitations and Insulator-Metal Transition in Poly(3-hexylthiophene) Organic Field-Effect Transistors

We carry out a comprehensive theoretical and experimental study of charge injection in Poly(3-hexylthiophene) (P3HT) to determine the most likely scenario for metal-insulator transition in this system. We calculate the optical absorption frequencies corresponding to a polaron and a bipolaron lattice in P3HT. We also analyze the electronic excitations for three possible scenarios under which a first-- or a second--order metal--insulator transition can occur in doped P3HT. These theoretical scenarios are compared with data from infrared absorption spectroscopy on P3HT thin film field-effect transistors (FET). Our measurements and theoretical predictions suggest that charge-induced localized states in P3HT FETs are bipolarons and that the highest doping level achieved in our experiments approaches that required for a first-order metal--insulator transition.Comment: 9 pages, 4 figures. Phys. Rev. B, in pres

Signatures of electron-boson coupling in half-metallic ferromagnet Mn5_5Ge3_3: study of electron self-energy Σ(ω)\Sigma(\omega) obtained from infrared spectroscopy

We report results of our infrared and optical spectroscopy study of a half-metallic ferromagnet Mn$_5$Ge$_3$. This compound is currently being investigated as a potential injector of spin polarized currents into germanium. Infrared measurements have been performed over a broad frequency (50 - 50000 cm$^{-1}$) and temperature (10 - 300 K) range. From the complex optical conductivity $\sigma(\omega)$ we extract the electron self-energy $\Sigma(\omega)$. The calculation of $\Sigma(\omega)$ is based on novel numerical algorithms for solution of systems of non-linear equations. The obtained self-energy provides a new insight into electron correlations in Mn$_5$Ge$_3$. In particular, it reveals that charge carriers may be coupled to bosonic modes, possibly of magnetic origin

Transport properties of chemically synthesized polypyrrole thin films

The electronic transport in polypyrrole thin films synthesized chemically from the vapor phase is studied as a function of temperature as well as of electric and magnetic fields. We find distinct differences in comparison to the behavior of both polypyrrole films prepared by electrochemical growth as well as of the bulk films obtained from conventional chemical synthesis. For small electric fields F, a transition from Efros-Shklovskii variable range hopping to Arrhenius activated transport is observed at 30 K. High electric fields induce short range hopping. The characteristic hopping distance is found to be proportional to F^(-1/2). The magnetoresistance R(B) is independent of F below a critical magnetic field, above which F counteracts the magnetic field induced localization.Comment: 6 pages, 5 figure

Localized and Delocalized Charge Transport in Single-Wall Carbon-Nanotube Mats

We measured the complex dielectric constant in mats of single-wall carbon-nanotubes between 2.7 K and 300 K up to 0.5 THz. The data are well understood in a Drude approach with a negligible temperature dependence of the plasma frequency (omega_p) and scattering time (tau) with an additional contribution of localized charges. The dielectric properties resemble those of the best ''metallic'' polypyrroles and polyanilines. The absence of metallic islands makes the mats a relevant piece in the puzzle of the interpretation of tau and omega_p in these polymers.Comment: 4 pages including 4 figure

Optical study on doped polyaniline composite films

Localization driven by disorder has a strong influence on the conducting property of conducting polymer. A class of authors hold the opinion that disorder in the material is homogeneous and conducting polymer is disordered metal close to Anderson-Mott Metal-Insulator transition, while others treat the disorder as inhomogeneous and have the conclusion that conducting polymer is a composite of ordered metallic regions and disordered insulating regions. The morphology of conducting polymers is an important factor that have influence on the type and extent of disorder. Different protonic acids used as dopants and moisture have affection on polymer chain arrangement and interchain interactions. A PANI-CSA film, two PANI-CSA/PANI-DBSA composite films with different dopants ratio, and one of the composite films with different moisture content are studied. Absolute reflectivity measurements are performed on the films. Optical conductivity and the real part of dielectric function are calculated by Kramers-Kronig(KK) relations. $\sigma_1(\omega)$ and $\epsilon_1(\omega)$ derivate from simple Drude model in low frequency range and tendencies of the three sample are different and non-monotonic. The Localization Modified Drude model(LMD) in the framework of Anderson-Mott theory can not give a good fit to the experimental data. By introducing a distribution of relaxation time into LMD, reasonable fits for all three samples are obtained. This result supports the inhomogeneous picture.Comment: 6 figures, 7 page

Impact Behavior of Composite Fan Blade Leading Edge Subcomponent with Thermoplastic Polyurethane Interleave

Impact damage tolerance and damage resistance is a critical metric for application of polymer matrix composites where failure caused by impact damage could compromise structural performance and safety. As a result, several materials and/or design approaches to improve impact damage tolerance have been investigated over the past several decades. Many composite toughening methodologies impart a trade-off between increased fracture toughness and compromised in-plane strength and modulus. In large part, mechanical tests to evaluate composite damage tolerance include static methods such as Mode I, Mode II, and mixed mode failures. However, ballistic impact damage resistance does not always correlate with static properties. The intent of this paper is to evaluate the influence of a thermoplastic polyurethane veil interleave on the static and dynamic performance of composite test articles. Static coupon tests included tension, compression, double cantilever beam, and end notch flexure. Measurement of the resistance to ballistic impact damage were made to evaluate the composites response to high speed impact. The interlayer material showed a decrease of in-plane performance with only a moderate improvement to Mode I and Mode II fracture toughness. However, significant benefit to impact damage tolerance was observed through ballistic tests

Insights from Australians with respiratory disease living in the community with experience of self-managing through an emergency department 'near miss' for breathlessness: A strengths-based qualitative study

© 2017 Article author(s). Objectives: Breathlessness 'crises' in people with chronic respiratory conditions are a common precipitant for emergency department (ED) presentations, many of which might be avoided through improved self-management and support. This study sought insights from people with experience of ED 'near misses' where they considered going to the ED but successfully self-managed instead. Design and methods: A qualitative approach was used with a phenomenological orientation. Participants: were eligible if they reported breathlessness on most days from a diagnosed respiratory condition and experience of ≥1 ED near miss. Recruitment was through respiratory support groups and pulmonary rehabilitation clinics. Semistructured interviews were conducted with each participant via telephone or face-to-face. Questions focused on ED-related decision-making, information finding, breathlessness management and support. This analysis used an integrative approach and independent coding by two researchers. Lazarus and Cohen's Transactional Model of Stress and Coping informed interpretive themes. Results: Interviews were conducted with 20 participants, 15 of whom had chronic obstructive pulmonary disease. Nineteen interviews were conducted via telephone. Analysis identified important factors in avoiding ED presentation to include perceived control over breathlessness, self-efficacy in coping with a crisis and desire not to be hospitalised. Effective coping strategies included: taking a project management approach that involved goal setting, monitoring and risk management; managing the affective dimension of breathlessness separately from the sensory perceptual and building three-way partnerships with primary care and respiratory services. Conclusions: In addition to teaching non-pharmacological and pharmacological management of breathlessness, interventions should aim to develop patients' generic self-management skills. Interventions to improve self-efficacy should ensure this is substantiated by transfer of skills and support, including knowledge about when ED presentation is necessary. Complementary initiatives are needed to improve coordinated, person-centred care. Future research should seek ways to break the cyclical relationship between affective and sensory-perceptual dimensions of breathlessness

Strong localization of electrons in quasi-one-dimensional conductors

We report on the experimental study of electron transport in sub-micron-wide ''wires'' fabricated from Si $\delta$-doped GaAs. These quasi-one-dimensional (Q1D) conductors demonstrate the crossover from weak to strong localization with decreasing the temperature. On the insulating side of the crossover, the resistance has been measured as a function of temperature, magnetic field, and applied voltage for different values of the electron concentration, which was varied by applying the gate voltage. The activation temperature dependence of the resistance has been observed with the activation energy close to the mean energy spacing of electron states within the localization domain. The study of non-linearity of the current-voltage characteristics provides information on the distance between the critical hops which govern the resistance of Q1D conductors in the strong localization (SL) regime. We observe the exponentially strong negative magnetoresistance; this orbital magnetoresistance is due to the universal magnetic-field dependence of the localization length in Q1D conductors. The method of measuring of the single-particle density of states (DoS) in the SL regime has been suggested. Our data indicate that there is a minimum of DoS at the Fermi level due to the long-range Coulomb interaction.Comment: 12 pages, 11 figures; the final version to appear in Phys. Rev.

Dopant-induced crossover from 1D to 3D charge transport in conjugated polymers

The interplay between inter- and intra-chain charge transport in bulk polythiophene in the hopping regime has been clarified by studying the conductivity as a function of frequency (up to 3 THz), temperature and doping level. We present a model which quantitatively explains the observed crossover from quasi-one-dimensional transport to three-dimensional hopping conduction with increasing doping level. At high frequencies the conductivity is dominated by charge transport on one-dimensional conducting chains.Comment: 4 pages, 2 figure

Illness Schema Activation and the Effects of Illness Seasonality on Accessibility of Implicit Illness-Related Information

The Common-Sense Model (CSM) of illness self-regulation is a leading theoretical framework describing the process by which an individual recognizes that he or she is physically ill and subsequently attempts to manage that illness state. The CSM proposes that people possess schematically organized implicit cognitive representations of health threats comprising information about illness such as symptoms, causes, label, duration, consequences, and procedures for managing threat [1, 2, 3, 4]. The proposed function of these stored knowledge structures is to activate a self-regulation process that might protect or restore a state of well-being [5]. The CSM proposes that the schematic representation is centrally activated by detection of deviations from the normal functioning self (i.e., experienced symptoms). The identification of illness and the initiation of self-management attempts follow from the search for illness-relevant cognitive structures and the matching of the content of illness schema to the symptomatic experience. For example, a headache (a symptomatic deviation from normal somatic experience) might activate illness schemata containing the cognitive representation of “headache” such as “hangover,” “dehydration,” or “flu.” The matching of the symptom to a particular illness schema will follow from the search and match to other aspects of plausible illness representations, such as its probable cause or duration (timeline).Full Tex