Monday, May 19, 2008

Conductors

Conductors can cause electricity to pass through it easily.

Transmission of electrons:
(Abraham Nitzan) Electron transmission through molecules and molecular interfaces has been a subject of intensive research due to recent interest in electron transfer phenomena underlying the operation of the scanning tunneling microscope (STM) on one hand, and in the transmission properties of molecular bridges between conducting leads on the other.
In these processes the traditional molecular view of electron transfer between donor and acceptor species give rise to a novel view of the molecule as a current carrying conductor, and observables such as electron transfer rates and yields are replaced by the conductivities, or more generally by current-voltage relationships, in molecular junctions.

(Noriaki Hamada et al.) There are variations in electronic transport in Carbon microtubules ( either they are metallic or semiconductors with narrow and moderate band gaps) depending on the diameter of the tubule and on the degree of helical arrangement of the carbon hexagons. This drastic variation in the band structure can be explained by the 2-dimensional band structure of graphite.
(Albert E. Seaver) Ohm's law (equation) is often used for the study of charge transport. When Ohm's law is combined with Gauss's law and the equation of continuity, a differential equation of volume charge density relaxation can be formed. The solution for this equation is material's permitivity divided by electrical conductivity that shows charge decays exponentially with a relaxation time.
Experiments show that good conductors follow a exponential decay and poor conductors show a decay which is more hyperbolic than exponential.

Following equation has been developed which can be used for both good conductors and poor insulators:



where
Pp is inserted charge
Pp0 is initial charge density
Tm is relaxation time constant
Tp is perturbation time constant.
(For further studies see references)
Properties of Conductors:
(J.B. Pendry et al.)Some microstructures, which are built from nonmagnetic conducting sheets, exhibit an effective magnetic permeability indicated by μeff, which can be tuned to values not accessible in naturally occurring materials, including large imaginary components of μeff.

Super conductors:
Extremely good conductors at low heat which produce no heat and causes no resistance. (Clovis Jacinto de Matos)There is a strong attractive gravitational forces between two electrons in superconductors which is concluded from the Eddington–Dirac large number relation, together with Beck and Mackey electromagnetic model of vacuum energy in superconductors.

Semi-Conductors:
Semi-conductors can pass electricity but not to that extent as conductors and they have the ability to pass electricity only at high temperatures.

Optical conductors:
Conductors which have the ability to pass light.

Transparent conductors:
(K. L. Chopra et al.) Studies are in process for the refinement and progress of transparent conductors. Non-stoichiometric, doped films of oxides of tin, indium, cadmium, zinc and their various alloys, deposited by numerous techniques, exhibit nearly metallic conductivity.

References:
Abraham Nitzan, Electron transmission through molecules and molecular interfaces. Condensed Matter

Albert E. Seaver, An Equation For Charge Decay Valid in Both Conductors
and Insulators.
Proceedings ESA-IEJ Joint Meeting 2002, Pages pp. 349-360.

Clovis Jacinto de Matos, Gravitational force between two electrons in superconductors. Physica C: Superconductivity, Volume 468, Issue 3, 1 February 2008, Pages 229-232.

J. B. Pendry, A. J. Holden, D. J. Robbins, W. J. Stewart, Magnetism from conductors and enhanced nonlinear phenomena. Ieee Transactions on Microwave Theory & Techniques , 1999Volume: 47, Issue: 11, Pages 2075-2084.

K. L. Chopra, S. Major, D. K. Pandya, Transparent conductors -- a status review. THIN SOL. FILMS. Vol. 102, no. 1, Pages, 1-46. 1983.

Noriaki Hamada, Shin-ichi Sawada, and Atsushi Oshiyama , New one-dimensional conductors: Graphitic microtubules. Physical review letters, 68, Pages 1579 - 1581 (1992)

Further Reading:
High Conductivity Solid Ionic Conductors: Recent Trends and Applications by International Conference on Solid State Ionics 1987 Garmisch-partenki

The Physics of Organic Superconductors and Conductors (Springer Series in Materials Science) by A. G. Lebed

Transparent Conductive Zinc Oxide: Basics and Applications in Thin Film Solar Cells by Klaus Ellmer, Andreas Klein, Bernd Rech

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