Investigation of the charge transport through disordered organic molecular heterojunctions

We develop a new three-dimensional multiparticle Monte Carlo ({\it 3DmpMC}) approach in order to study the hopping charge transport in disordered organic molecular media. The approach is applied here to study the charge transport across an energetically disordered organic molecular heterojunction, known to strongly influence the characteristics of the multilayer devices based on thin organic films. The role of energetic disorder and its spatial correlations, known to govern the transport in the bulk, are examined here for the bilayer homopolar system where the heterojunction represents the bottleneck for the transport. We study the effects of disorder on both sides of the heterojunction, the effects of the spatial correlation within each material and among the layers. Most importantly, the {\it 3DmpMC} approach permits us to treat correctly the effects of the Coulomb interaction among carriers in the region where the charge accumulation in the device is particularly important and the Coulomb interaction most pronounced. The Coulomb interaction enhances the current by increasing the electric field at the heterojunction as well as by affecting the thermalization of the carriers in front of the barrier. Our MC simulations are supplemented by the master equation (ME) calculations in order to build a rather comprehensive picture of the hopping transport over the homopolar heterojunction.Comment: 26 pages, 11 figures, LaTe

In the eyes of Janus:the intellectual structure of HRM-performance debate and its future prospects

Purpose The purpose of this paper is to offer a perspective on the future of the human resource management (HRM)-performance debate and its prospects for interaction with practice by evaluating the debate's intellectual structure. Design/methodology/approach With co-citation analysis the paper examines the intellectual structure that informed the HRM-performance debate. The findings were presented to a group of academics, who have been influential in the development of the debate. In several rounds of a quasi-Delphi interaction they discussed the state of the art, future development of the debate, upcoming theoretical sources of inspiration and topics on which they (dis)agreed. Findings The dominant knowledge domain is built upon resource-based view, social exchange theory, human capital theory, institutional theory and critical perspective. It became well established in the mid 1990s, when the strategic HRM domain merged with the high performance work systems domain, thus forming the conceptual backbone of the debate. More recently the debate has been informed by review studies, meta-analyses and critical reflections on the current methodological paradigms, which is aligned with the debate's life cycle stage. Originality/value The paper highlights the theoretical foundations of the HRM-performance debate and gives valuable suggestions on how to take the field forward along with important implications for researchers and their relationship with the business community. Keywords: High performance work systems, HR strategy, Organization effectivenes

Optical Susceptibilities of Polymers: Current-Current versus Dipole-Dipole Correlation

The static current operator leads to definitional zero frequency divergence and unphysical results in studying nonlinear optical susceptibilities of polymers. A well-defined dipole-dipole correlation is superior to the complicated current-current correlation to solve this problem. As illustrative examples, optical susceptibilities under both SSH and TLM models of trans-(CH)_x are studied. New analytical results are obtained. The reasons of previous improper results are analyzed

Looking beyond - socialization tactics:The role of human resource systems in the socialization process

Previous research questions whether the association between socialization tactics and human resource systems has been properly explored. Based on theory, we present a framework that links socialization tactics and human resource systems for various groups of newcomers. In doing so, we contribute to academic theory by exploring the under-researched areas of the content and context of socialization tactics, while illustrating helpful practices to retain key newcomers in organizations. The article provides new insights into socialization tactics and human resource systems by bridging the two theoretical areas, opening up this conceptual space for examination by organizational scholars. We also discuss the theoretical and practical implications for human resource scholars and practitioners accordingly

Fats and function:protein lipid modifications in plant cell signalling

The post-translational lipid modifications N-myristoylation, prenylation and S-acylation are traditionally associated with increasing protein membrane affinity. However this is an over-simplification, with evidence now implicating these modifications in a variety of roles such as membrane microdomain partitioning, protein trafficking, protein complex assembly and polarity maintenance. Evidence for a regulatory role is also emerging, with changes or manipulation of lipid modifications offering a means of directly controlling various aspects of protein function. Proteomics advances have revealed an enrichment of signalling proteins in the lipid-modified proteome, potentially indicating an important role for these modifications in responding to stimuli. This review highlights some of the key themes and possible functions of lipid modification during signalling processes in plants

Photoinduced charge separation in Q1D heterojunction materials: Evidence for electron-hole pair separation in mixed-halide MXMX solids

Resonance Raman experiments on doped and photoexcited single crystals of mixed-halide $MX$ complexes ($M$=Pt; $X$=Cl,Br) clearly indicate charge separation: electron polarons preferentially locate on PtBr segments while hole polarons are trapped within PtCl segments. This polaron selectivity, potentially very useful for device applications, is demonstrated theoretically using a discrete, 3/4-filled, two-band, tight-binding, extended Peierls-Hubbard model. Strong hybridization of the PtCl and PtBr electronic bands is the driving force for separation.Comment: n LaTeX, figures available by mail from JTG ([email protected]

Excitation Spectrum of One-dimensional Extended Ionic Hubbard Model

We use Perturbative Continuous Unitary Transformations (PCUT) to study the one dimensional Extended Ionic Hubbard Model (EIHM) at half-filling in the band insulator region. The extended ionic Hubbard model, in addition to the usual ionic Hubbard model, includes an inter-site nearest-neighbor (n.n.) repulsion, $V$. We consider the ionic potential as unperturbed part of the Hamiltonian, while the hopping and interaction (quartic) terms are treated as perturbation. We calculate total energy and ionicity in the ground state. Above the ground state, (i) we calculate the single particle excitation spectrum by adding an electron or a hole to the system. (ii) the coherence-length and spectrum of electron-hole excitation are obtained. Our calculations reveal that for V=0, there are two triplet bound state modes and three singlet modes, two anti-bound states and one bound state, while for finite values of $V$ there are four excitonic bound states corresponding to two singlet and two triplet modes. The major role of on-site Coulomb repulsion $U$ is to split singlet and triplet collective excitation branches, while $V$ tends to pull the singlet branches below the continuum to make them bound states.Comment: 10 eps figure

Pressure Tuning of the Charge Density Wave in the Halogen-Bridged Transition-Metal (MX) Solid Pt2Br6(NH3)4Pt_2Br_6(NH_3)_4

We report the pressure dependence up to 95 kbar of Raman active stretching modes in the quasi-one-dimensional MX chain solid $Pt_2Br_6(NH_3)_4$. The data indicate that a predicted pressure-induced insulator-to-metal transition does not occur, but are consistent with the solid undergoing either a three-dimensional structural distortion, or a transition from a charge-density wave to another broken-symmetry ground state. We show that such a transition cacan be well-modeled within a Peierls-Hubbard Hamiltonian. 1993 PACS: 71.30.+h, 71.45.Lr, 75.30.Fv, 78.30.-j, 81.40.VwComment: 4 pages, ReVTeX 3.0, figures available from the authors on request (Gary Kanner, [email protected]), to be published in Phys Rev B Rapid Commun, REVISION: minor typos corrected, LA-UR-94-246