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Title: Understanding resonant tunnel transport in non-identical and non-aligned clusters as applied to disordered carbon systems

Abstract

We study the conductance spectra and the corresponding current-voltage characteristics of a set of three impurity clusters of different sizes arranged in the form of a scalene triangle and compare with the transport of their horizontal and vertical configurations. The tuning capability of resonant tunnelling features in a quantum dot device made of these non-aligned impurity clusters is demonstrated by re-distributing their diameters and inter-cluster distances in a systematic manner. By manipulating the inter-cluster coupling for a scalene triangular configuration, the transition of current-voltage curves from a step-like feature to a negative differential resistance can be produced. This process also yields conductance features for triangular configurations, which can be compared to the quantum dot structures perfectly aligned to the direction of the propagating wavevector. The strength of inter-cluster coupling or order parameter for these configurations is analysed from the relative variation of the width and the energy difference of the sharp and broad peaks observed in the density of states spectra. Based on the relative change of the inter-cluster coupling with the cluster configurations, a transport model applicable to structurally inhomogeneous systems is proposed in order to explain the experimentally observed variation of the energy band gap with the disordermore » parameters.« less

Authors:
 [1];  [2];  [1]
  1. Nano-Scale Transport Physics Laboratory, School of Physics, University of the Witwatersrand, Private Bag 3, WITS 2050 Johannesburg (South Africa)
  2. (United Kingdom)
Publication Date:
OSTI Identifier:
22305840
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 116; Journal Issue: 15; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; CARBON; COMPARATIVE EVALUATIONS; COUPLING; CURRENTS; ELECTRIC CONDUCTIVITY; IMPURITIES; ORDER PARAMETERS; QUANTUM DOTS; SPECTRA; TRIANGULAR CONFIGURATION; TUNNEL EFFECT

Citation Formats

Bhattacharyya, Somnath, E-mail: Somnath.Bhattacharyya@wits.ac.za, School of Physics and Astronomy, University of Leeds, E C Stoner Laboratory, Leeds LS2 9JT, and Churochkin, Dmitry. Understanding resonant tunnel transport in non-identical and non-aligned clusters as applied to disordered carbon systems. United States: N. p., 2014. Web. doi:10.1063/1.4898801.
Bhattacharyya, Somnath, E-mail: Somnath.Bhattacharyya@wits.ac.za, School of Physics and Astronomy, University of Leeds, E C Stoner Laboratory, Leeds LS2 9JT, & Churochkin, Dmitry. Understanding resonant tunnel transport in non-identical and non-aligned clusters as applied to disordered carbon systems. United States. doi:10.1063/1.4898801.
Bhattacharyya, Somnath, E-mail: Somnath.Bhattacharyya@wits.ac.za, School of Physics and Astronomy, University of Leeds, E C Stoner Laboratory, Leeds LS2 9JT, and Churochkin, Dmitry. Tue . "Understanding resonant tunnel transport in non-identical and non-aligned clusters as applied to disordered carbon systems". United States. doi:10.1063/1.4898801.
@article{osti_22305840,
title = {Understanding resonant tunnel transport in non-identical and non-aligned clusters as applied to disordered carbon systems},
author = {Bhattacharyya, Somnath, E-mail: Somnath.Bhattacharyya@wits.ac.za and School of Physics and Astronomy, University of Leeds, E C Stoner Laboratory, Leeds LS2 9JT and Churochkin, Dmitry},
abstractNote = {We study the conductance spectra and the corresponding current-voltage characteristics of a set of three impurity clusters of different sizes arranged in the form of a scalene triangle and compare with the transport of their horizontal and vertical configurations. The tuning capability of resonant tunnelling features in a quantum dot device made of these non-aligned impurity clusters is demonstrated by re-distributing their diameters and inter-cluster distances in a systematic manner. By manipulating the inter-cluster coupling for a scalene triangular configuration, the transition of current-voltage curves from a step-like feature to a negative differential resistance can be produced. This process also yields conductance features for triangular configurations, which can be compared to the quantum dot structures perfectly aligned to the direction of the propagating wavevector. The strength of inter-cluster coupling or order parameter for these configurations is analysed from the relative variation of the width and the energy difference of the sharp and broad peaks observed in the density of states spectra. Based on the relative change of the inter-cluster coupling with the cluster configurations, a transport model applicable to structurally inhomogeneous systems is proposed in order to explain the experimentally observed variation of the energy band gap with the disorder parameters.},
doi = {10.1063/1.4898801},
journal = {Journal of Applied Physics},
number = 15,
volume = 116,
place = {United States},
year = {Tue Oct 21 00:00:00 EDT 2014},
month = {Tue Oct 21 00:00:00 EDT 2014}
}
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  • The Raman spectra of a wide range of disordered and amorphous carbons have been measured under excitation from 785 to 229 nm. The dispersion of peak positions and intensities with excitation wavelength is used to understand the nature of resonant Raman scattering in carbon and how to derive the local bonding and disorder from the Raman spectra. The spectra show three basic features, the D and G around 1600 and 1350 cm{sup -1} for visible excitation and an extra T peak, for UV excitation, at {approx}1060 cm{sup -1}. The G peak, due to the stretching motion of sp{sup 2} pairs,more » is a good indicator of disorder. It shows dispersion only in amorphous networks, with a dispersion rate proportional to the degree of disorder. Its shift well above 1600 cm{sup -1} under UV excitation indicates the presence of sp{sup 2} chains. The dispersion of the D peak is strongest in ordered carbons. It shows little dispersion in amorphous carbon, so that in UV excitation it becomes like a density-of-states feature of vibrations of sp{sup 2} ringlike structures. The intensity ratio I(D)/I(G) falls with increasing UV excitation in all forms of carbon, with a faster decrease in more ordered carbons, so that it is generally small for UV excitation. The T peak, due to sp{sup 3} vibrations, only appears in UV Raman, lying around 1060 cm{sup -1} for H-free carbons and around 980 cm{sup -1} in hydrogenated carbons. In hydrogenated carbons, the sp{sup 3}C-H{sub x} stretching modes around 2920 cm{sup -1} can be clearly detected for UV excitation. This assignment is confirmed by deuterium substitution.« less