Mesoscopic charge transport

Landauer proposed in 1957 the first mesoscopic theoretical approach to charge transport [176]. Transport is treated as a scattering problem, ignoring initially all inelastic interactions. Phase coherence is assumed to be preserved within the entire conductor. Transport properties, such as the electrical conductance, are intimately related to the transmission probability for an electron to cross the system. Landauer considered the current as a consequence of the injection of electrons at one end of a sample, and the probability of the electrons reaching the other end. The total conductance is determined by the sum of all current-carrying eigenmodes and their transmission probability, which leads to the Landauer formula of a ID system ... 

Dye-sensitized systems are not suited to interpretation by conventional device physics methods on account of two features firstly, the mesoscopic phase separation of electron and hole conductors, which makes the porous material unable to sustain large electric fields and secondly, the separation, through the use of sensitizers, of optical absorption from charge transport in either material. Efforts to understand the photovoltaic action of the DSSC are leading to a reassessment of basic principles and the possibilities of novel photovoltaic designs. 

Many nanoscale energy conversion devices, like dye-sensitized and pol5mer-based solar cells, rely on efficient interfacial electron transfer processes. Multiscale modelling of such devices ultimately involves length-and time-scales that scan many orders of magnitude, ranging from ultrafast molecular-scale quantum phenomena such as photoinduced electron transfer, via mesoscopic properties such as charge transport, to macroscopic device performance such as I-V characteristics. 

In mesoscopic physics, because the geometries can be controlled so well, and because the measurements are very accurate, current under different conditions can be appropriately measured and calculated. The models used for mesoscopic transport are the so-called Landauer/Imry/Buttiker elastic scattering model for current, correlated electronic structure schemes to deal with Coulomb blockade limit and Kondo regime transport, and charging algorithms to characterize the effects of electron populations on the quantum dots. These are often based on capacitance analyses (this is a matter of thinking style - most chemists do not consider capacitances when discussing molecular transport junctions). 

Spintronics [136-138] is a word used to describe transport in a mesoscopic junction in which the transport medium (or the electrodes) contain unpaired electron spins. There are different aspects of spintronics, but the simplest idea is that one can transport spin without necessarily transporting charge. This leads to the idea of a molecular spin transistor, and other spin phenomena such as spin valves and spin gates. 

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