Chapter 8
Molecular-Scale Electronics
‘I don't like electrons; they've always had a negative influence on society’
Chris Lipe
8.1 Electron Transfer and Molecular Junctions
Electron transfer phenomena are the most important processes in chemistry [1]. Virtually the same processes are observed when: (i) electron is transferred inside a molecule from a donor to an acceptor moiety along a molecular bridge, (ii) an electron is injected from an excited molecule to the conduction band of a semiconductor, or (iii) electrons pass along a single molecule sandwiched between two metallic pads (Figure 8.1). The last is referred to as a molecular junction, provided its electron transport properties show some molecular signatures [2].
Figure 8.1 Different molecular assemblies for electron transport processes: donor–bridge–acceptor molecule (a), molecule attached to one electrode (b) and molecule sandwiched between electrodes (c). Adapted from [1] Copyright (2003) American Chemical Society.
From the point of view of infochemical applications and molecular-level electronics the third case is the most interesting. Due to the different chemical characters of the molecules involved in the formation of a molecular junction, four different classes of these systems can be delineated (Figure 8.2). In the simplest case just an alkane chain can join two conductors (Figure 8.2a). More sophisticated behaviour ...
