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Organic and Molecular Electronics
Crystals and films of conjugated molecules transport charge and can be used as functional semiconductors in thin film transistors, photovoltaic cells and light-emitting diodes. My research program focuses on understanding connections between structure and electrical transport behavior in organic semiconductors. We are particularly interested in the dependence of electron and hole mobility (the velocity per unit electric field) on molecular structure, crystal packing, intermolecular bonding, and defects in organic crystals and films. A theme of our experimental investigations is the development of methods for measuring transport behavior on length scales spanning nanometers to microns, so that we can accurately characterize the effects of specific structural features on transport. For example, we have used high resolution scanning probe microscopy techniques to measure electrical resistances and potential variations associated with individual grain boundaries in organic semiconductor films. Students are also actively involved in the fabrication and electrical characterization of organic transistors using electron beam lithography and other semiconductor processing equipment in the Microtechnology Laboratory. In collaboration with students and faculty in the chemistry and physics departments, we are actively exploring the synthesis and characterization of novel organic semiconductor materials with enhanced transport properties.
We are also interested in electrical transport through individual molecules. A key issue in molecular electronics is how one "wires up" single molecules or groups of molecules. We use conducting probe atomic force microscopy to contact small numbers of molecules and to test their electrical properties. Questions of interest include how the current-voltage characteristics of these molecular junctions depend on molecular size, bonding and functional group architecture, and the nature of the metal-molecule contacts.