Coulomb blockade currents measured in a conducting polymer monolayer and a 2D charge transport model. Background is schematic of the monolayer on electrodes. Credit: Image courtesy of Osaka University
Generally, organic conductors has disorder structures so charge transfers from one place with high conductivity to another place with high conductivity. In such occasions, Coulomb blockade of charge transport takes place. It was thought Coulomb blockade took place in low dimensional aggregates of inorganic particulates only at very low temps.
Osaka Uni researchers succeeded in showing experimental evidence to prove Coulomb blockade taking place on 2D organic conducting polymer films. They also demonstrated its theoretical evidence through quantum calculations and the verification of conductivity models of experimental results. This research will possibly overturn conventional understanding of conduction mechanism of organic conductors and help one to understand and design properties of organic and molecular devices.
Organic devices have grown remarkably. Among them, conductive polymers in particular are synthesized from inexpensive carbon-based low molecules, and their properties can be changed into metals, semiconductors, and insulators by changing their structure and doping to be used for various devices. Low temp properties are very important in learning the essence of conduction. In organic materials, peculiar nonlinearity to current voltage, which is different from inorganics appears. Nonlinear conductivity has been considered one of the mysteries of organic condensed matter physics.
They created 2D ultrathin-films of regularly arranged hexylthiophene (P3HT) monolayers and attached the sheet of about 1-nm monolayer to a metal electrode with a gap of less than a micrometer and measured electrical conductivity. The current flowing in the molecular membrane showed the temperature-dependent threshold voltage in the low temperature range of 150K — 4K and increased in power law of the current-voltage beyond the threshold. This is a typical feature of Coulomb blockade. This group theoretically verified onset of 2D Coulomb blockade in the organic thin film through calculation of the delocalization of electric charge in the molecular film and the verification of a distribution model of conductive segment in the film. This group’s achievement suggests that in organic conductors, Coulomb blockade affects conductivity at room temperature as well. http://resou.osaka-u.ac.jp/en/research/2015/20151109_1
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