Patrick Group - Ordered Molecular Materials

We use a combination of experiment and theory to study the chemical physics of crystallization in simple molecular semiconductor materials such as tetracene and pentacene, as well as fabricate and characterize the performance of devices such as organic field-effect transistors.  Our group has developed a powerful new approach for preparing films of these materials called organic vapor-liquid-solid (OVLS) deposition, which produces much larger crystals with more highly controlled growth characteristics than one can achieve by conventional methods.  In OVLS deposition, the substrate is coated by a thin organic solvent layer, into which a flux of molecular growth units is supplied carried by an impinging gas flow under near-ambient conditions. As the solvent layer becomes saturated, crystals form in a quasi-two dimensional liquid environment, but they tend to stay in fixed positions, similar to island growth on bare surfaces.

Much of our research involves thermotropic liquid crystals (LCs), which we study both in their own right, as fascinating and useful materials, but also in less conventional applications, as solvents for controlling the organization of molecules and small particles.  Liquid crystals are familiar to most people from liquid crystal displays, but they are used in a variety of other applications as well, from thermometers to switchable privacy windows.  Like conventional liquids, they flow and can be mixed with other substances, but unlike conventional liquids, in which the molecules are randomly oriented and randomly positioned, the molecules in a liquid crystal have orientational and/or positional order.  Some of our work involves polymerizable LCs, also called reactive mesogens. These are liquid crystalline compounds with reactive functional groups that can be thermally or photoreactively cross-linked, "locking in" orientation to prepare oriented polymer thin films.