1,721,161 research outputs found
Numerical investigation of non-ohmic hopping conduction in macroscopically non-homogeneousthin layers. Weak electron-phonon interaction
No full textThe current-field and the conductivity-field characteristics of random hopping non-uniform systems in the limit of a weak electron-phonon coupling (band-like hopping transport in disordered solids) have been calculated numerically within the Bottger-Bryksin model. In particular, we consider thin layers placed between two planar Ohmic contacts, with exponential spatial variations in the total centre concentration over the layer thickness. We find that firstly for r-hopping transport in spatially uniform layers the current decreases with increasing field, reaching a constant saturation value, and on increasing the degree of non-uniformity the saturation current becomes lower and secondly both uniform and non-uniform r- epsilon -hopping systems are almost exactly Ohmic in the investigated field range; conductivity decreases on increasing the degree of non-uniformity of the centre distribution. Degree of the layer non-uniformity in the limit of weak electron-phonon coupling are quite different from the dependences in the case of strong electron-phonon coupling. The dependences on the degree of the layer non-uniformity of the centre distribution. The dependences on the degree of the layer non-uniformity in the limit of weak electron-phonon coupling are quite different from the dependences in the case of strong electron-phonon coupling
A new program package for investigation of medium-range order in computer-simulated solids
No full textThe opportunity to gain detailed information on the representative sets of rings, and chains of atoms is of great importance in the analysis of medium-range order in the computer-simulated structures of solids. In this paper, a new program package (ANELLI) for ring and chain analysis of computer-simulated atomic structures is presented, and examples are given of its usage
Numerical investigation of non-ohmic hopping conduction in macroscopically non-homogeneousthin layers. Strong electron-phonon interaction
No full textThe current-field and conductivity-field characteristics of random r hopping as well as r-E hopping systems with a strong electron-phonon coupling have been calculated numerically and discussed by Bottger and co-workers (1985-86). They have assumed a random but macroscopically homogeneous distribution of centres over the sample. However, in most real cases an extremely thin layer can hardly be thought to be macroscopically homogeneous and the local hopping-centre density should depend on the distance from the electrodes. In the present work the authors apply the Bottger-Wegener procedure to random r hopping and r-E hopping systems with macroscopic average density exponentially dependent on the distance from the contact. Only a strong electron-phonon coupling will be considered, i.e. the authors shall consider small-polaron transport in a disordered solid. The influence of the inhomogeneity in the centre distribution on current field and conductivity-field characteristics may be summarized as follows. Firstly, for r-hopping transport in homogeneous layers, Bottger and Wegener observe a decrease in the differential conductivity with increasing field, its local minimum being followed by an exponential increase; the authors confirm the results for homogeneous systems, whereas for inhomogeneous systems they find that, on increasing the degree of the site distribution inhomogeneity the local conductivity minimum is no longer followed by an exponential conductivity increase, but the system becomes ohmic (conductivity saturation), at least up to the fields consistent with the assumption of constant carrier concentration. Secondly, for r-E hopping in homogeneous layers, Bottger et al. observe for not too high an energy spread in the hopping centres that the local conductivity maximum occurring just after the ohmic region is followed by a local minimum, that latter being followed by an exponential conductivity increase for still higher fields
Structure of partially reduced xPbO (1-x)SiO2 glasses: combined EXAFS and MD study
No full textWe have studied the structure of partially reduced lead-silicate glasses using combined EXAFS (extended X-ray absorption fine structure) and MD (molecular dynamics) methods. The analysis was performed for glasses of x[(l - p)Pb pPbO] (I - X)SiO2 composition, x = 0.3,0.5,0.7, where parameter (I - p) describes the degree of reduction, i.e. the content of the granular metallic phase, appearing as the result of the reduction process (e.g. annealing in hydrogen atmosphere). In the EXAFS experiment (1 - p) was expressed via the time of reduction realized at 400 degrees C (1.5 It, 24 It, 70 h), whereas in the MD simulations it was determined precisely by using proper numbers of particles (corresponding to (1 - p) = 0.0, 0.25, 0.5, 0.75 and 1.0). In the paper we describe in detail the local structure around lead atoms and its changes in the function of glass composition and reduction degree. The tendency for agglomeration of Pb-0 into clusters, the formation of the granular metallic phase, and continuity of silica and lead oxide subnetworks are discussed. A good agreement between EXAFS-extractcd and MD-extracted parameters of the short-range structure encouraged us to preform a medium-range order analysis, based on the MD simulations only. Moreover, combining the EXAFS and MD methods we could correlate the reduction time (technological parameter) with the degree of reduction (I - p) and the actual state of the granular structure. The latter relation may be useful for controlled production of reduced glasses of pre-requested physical properties. (c) 2005 Elsevier B.V. All rights reserved
Magnetoresistance in triphenyl-diamine derivative blue organic light emitting devices
No full textCopyright 2008 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. This article appeared in Journal of Applied Physics 103, 043706 (2008) and may be found at
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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