The dependence of hopping conductance on temperature and voltage for an ensemble of modestly long one-dimensional wires is studied numerically using the shortest-path algorithm. In a wide range of parameters this dependence can be approximated by a power law rather than the usual stretched-exponential form. The relation to recent experiments and prior analytical theory is discussed.

http://absimage.aps.org/image/MAR11/MWS_MAR11-2010-003748.pdf

Apparent Power-Law Behavior of Conductance in Disordered Quasi-One-Dimensional Systems

We investigate the direct-current response of crystalline organic semiconductors in the presence of finite external electric fields by the quantum-classical Ehrenfest dynamics complemented with instantaneous decoherence corrections (IDC). The IDC is carried out in the real-space representation with the energy-dependent reweighing factors to account for both intermolecular decoherence and energy relaxation by which conduction occurs. In this way, both the diffusion and drift motion of charge carriers are described in a unified framework. Based on an off-diagonal electron-phonon coupling model for pentacene, we find that the drift velocity initially increases with the electric field and then decreases at higher fields due to the Wannier-Stark localization, and a negative electric-field dependence of mobility is observed. The Einstein relation, which is a manifestation of the fluctuation-dissipation theorem, is found to be restored in electric fields up to ~$10^5$ V/cm for a wide temperature region studied. Furthermore, we show that the incorporated decoherence and energy relaxation could explain the large discrepancy between the mobilities calculated by the Ehrenfest dynamics and the full quantum methods, which proves the effectiveness of our approach to take back these missing processes.

Drift of Charge Carriers in Crystalline Organic Semiconductors

...................................................................... 1 Resumen...................................................................... 6 Brief Overview ............................................................. 10 Chapter 1...................................................................... 12

Transport mechanisms study in graphite oxide platelets obtained from bamboo for possible applications in electronic [recurso electrónico]

Die vorliegende Arbeit beschaftigt sich mit der Herstellung, der Optimierung
sowie mit der numerischen Simulation von Polymer-OLEDs, bei denen
Natriumstearat als alternativer Elektroneninjektor fungiert Gegenuber der standardmasig eingesetzten, anorganischen und toxischen Substanz Lithiumfluorid besitzt Natriumstearat den Vorteil, sowohl organisch als auch ungiftig zu sein, denn im Zeitalter der Massenproduktion elektronischer Gerate gewinnt die Umweltvertraglichkeit der verwendeten Materialien zunehmend an Bedeutung

Die Optimierung der hergestellten OLEDs erfolgt ua mit Hilfe von Bauteilsimulationen Weil sich kommerzielle Simulatoren fur diesen Zweck aufgrund der besonderen Injektionseigenschaften von Natriumstearat als
ungeeignet erwiesen, wird im Rahmen dieser Arbeit ein Simulationsprogramm
entwickelt und verwendet, welches speziell auf die Eigenschaften der untersuchten Leuchtdioden zugeschnitten ist
This thesis deals with the fabrication, optimization and numerical simulation of polymer light-emitting diodes using sodium stearate as an alternative electron injector In contrast to lithium fluoride, the most popular electron injector, sodium stearate has the advantage to be an organic and non-toxic material, since in the era of mass production and throw-away electronics, the environmental safety of the utilized materials is an important concern

Device simulations are used to optimize the fabricated OLEDs Due to the special injection properties of sodium stearate, commercial simulators turned out to be not suitable for this purpose Thus, in this thesis, a simulation program is developed, which fits the requirements and characteristics of the investigated devices

Herstellung, Optimierung und numerische Simulation von Polymer-Leuchtdioden mit Natriumstearat als Elektroneninjektor

......................................................................................................................... ii Acknowledgements ....................................................................................................... iv Table of contents ............................................................................................................ v 1. CHAPTER 1: INTRODUCTION....................................................... 1 1.1 Thermoelectrics.................................................................................................2 1.1.1 Overview and applications........................................................................2 1.1.2 Thermoelectric figure of merit and limiting value....................................4 1.1.3 Materials for thermoelectric energy conversion .......................................9 1.2 Skutterudites....................................................................................................13 1.2.1 Structure ..................................................................................................13 1.2.2 Ternary skutterudites...............................................................................16 1.2.3 Filled skutterudites ..................................................................................17 1.2.4 Thermoelectric properties of binary, ternary and filled skutterudites.....22 1.2.5 Anomalous phenomena in filled skutterudites........................................24 1.3 Equiatomic ternary phases ..............................................................................26 1.3.1 ZrSiS-type ...............................................................................................26 1.3.2 Anion-anion pair-forming phases ...........................................................28 FeS2 pyrite archetype ..............................................................................29 NiSbS ullmannite .....................................................................................30 CoAsS cobaltite .......................................................................................31 FeAsS asenopyrite ...................................................................................33 α-NiAs2-type ............................................................................................36 1.4 Shandites .........................................................................................................38 1.4.1 Metal-rich chalcogenides ........................................................................38 1.4.2 Shandite structure....................................................................................41 1.4.3 Parkerite structure ...................................................................................44 1.4.4 Structural relation between parkerite and shandite .................................45 1.4.5 Bonding in shandites ...............................................................................46 1.4.6 Electronic transport in shandites and parkerites......................................46 1.4.7 Half-metallicity and spintronics..............................................................48

Structural study and thermoelectric properties of some group 9 ternary metal chalcogenides

The conductivity of an $n$-type semiconductor has been calculated in the region of low-temperature $T$ and low impurity concentration ${n}_{D}$. The model is that of phonon-induced electron hopping from donor site to donor site where a fraction $K$ of the sites is vacant due to compensation. To first order in the electric field, the solution to the steady-state and current equations is shown to be equivalent to the solution of a linear resistance network. The network resistance is evaluated and the result shows that the $T$ dependence of the resistivity is $\ensuremath{\rho}\ensuremath{\propto}\mathrm{exp}(\frac{{\ensuremath{\epsilon}}_{3}}{\mathrm{kT}})$. For small $K$, ${\ensuremath{\epsilon}}_{3}=(\frac{{e}^{2}}{{\ensuremath{\kappa}}_{0}}){(\frac{4\ensuremath{\pi}{n}_{D}}{3})}^{\frac{1}{3}}(1\ensuremath{-}1.35{K}^{\frac{1}{3}})$, where ${\ensuremath{\kappa}}_{0}$ is the dielectric constant. At higher $K$, ${\ensuremath{\epsilon}}_{3}$ and $\ensuremath{\rho}$ attain a minimum near $K=0.5$. The dependence on ${n}_{D}$ is extracted; the agreement of the latter and of ${\ensuremath{\epsilon}}_{3}$ with experiment is satisfactory. The magnitude of $\ensuremath{\rho}$ is in fair agreement with experiment. The influence of excited donor states on $\ensuremath{\rho}$ is discussed.

Allen H. Miller

Papers

Impurity Conduction at Low Concentrations.