Patrick Group - Ordered Molecular Materials

1. Nucleation and Crystal Growth in Organic Semiconductor Films

tetracene films

Modern electronics are mostly based on inorganic semiconductors like silicon.  For some applications though, major cost or performance advantages could in principle be gained by using molecular semiconductors instead, composed of polymers or small molecules.  Examples include less expensive, higher performance solar cells, thin, mechanically flexible displays, and lower cost, higher efficiency lighting.  Our research on molecular crystallization is aimed at better understanding nucleation and growth of small-molecule organic semiconductors to help improve their performance for electronic and optoelectronic applications.

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.

OVLS Schematic
Student uses chamber

Film formation thus combines elements of physical vapor deposition and solution-phase crystal growth.  Crystal nucleation and growth is observed in situ using sophisticated videomicroscopy imaging techniques, producing movies that can be analyzed frame-be-frame to learn about crystal nucleation and growth rates, size- and spatial distributions.  The resulting statistical descriptions are analyzed in the framework of kinetic and thermodynamic models which helps to enable broad generalizations about the design rules governing molecular crystallization.


  • "Multi-Scale Modeling of Early-State Morphology in Solution-Processed Polycrystalline Thin Films", Patrick, D.L.; Schaaf, C.#; Morehouse, R.*; Johnson, B. L. Phys. Chem. Chem. Phys. 2019, in press.
  • "Predictive modeling of nanoscale domain morphology in solution-processed organic thin films", Schaaf, C.; Jenkins, M.; Morehouse, R.; Stanfield, D.; McDowall, S.; Johnson, B.L.; Patrick, D.L. Phys. Rev. Mater20171, 043404. 
  • "High performance organic field-effect transistors using ambient deposition of tetracene single crystals", Morrison, L. A.; Stanfield, D.; Jenkins, M.; Baronov, A. A.; Patrick., D. L.; Leger, J. M. Organic Electronics 201633, 269. 
  • "A simple model of burst nucleation", Aleksandr Baronov, Kevin Bufkin, Daniel W. Shaw, Brad. L. Johnson, D. L. Patrick, Phys. Chem. Chem. Phys201517, 20846.  
  • "Organic-vapor-liquid-solid deposition with an impinging gas jet”, Daniel W. Shaw, Kevin Bufkin, Alexandr A. Baronov, Brad L. Johnson, and David L. Patrick, J. Appl. Phys.2012. 111, 074907.
  • "Engineered Growth of Organic Crystalline Films Using Liquid Crystal Solvents", F. Scott Wilkinson, R. F. Norwood, Joseph M. McLellan, L. Rhys Lawson, David L. Patrick, J. Am. Chem. Soc.2006 128, 16468. 

2. Liquid Crystal Solvents

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.

LC imprinting diagram
STM image
lc stamping schematic

We develop unconventional applications of liquid crystals, especially their use as media for controlling order in other molecular materials.  Our group was the first to demonstrate the use of LC solvents for depositing oriented films of molecules and small particles such as carbon nanotubes, and we are currently developing concepts for LC-based inks that can be used to print organized molecular films using patterned anchoring stamps.


  • "Stamping oriented molecular monolayers using liquid crystal inks”, R. Thompson, C. Lund, S. A. Hickman, E. Krohn, D. L. Patrick, Chem. Comm.2011. Edit media
  • Oriented SWCNTs
  • “Hierarchical Order in Organic Monolayers Deposited From Liquid Crystal Solvents”, N. Gislason, C. Murphy, D. L. Patrick, J. Phys. Chem. C2010 114, 12659. 
  • "Engineered Growth of Organic Crystalline Films Using Liquid Crystal Solvents", F. Scott Wilkinson, R. F. Norwood, Joseph M. McLellan, L. Rhys Lawson, David L. Patrick, J. Am. Chem. Soc.2006 128, 16468. 
  • Getting Organized at the Nanoscale with Liquid Crystal Solvents, D. L. Patrick, F. Scott Wilkinson, T. L. Fegurgur, Proc. SPIE, 5936, 5936A (2005).  
  • Controlling the Orientation of Micron-Sized Rod-Shaped SiC Particles with Nematic Liquid Crystal Solvents, M. D. Lynch, Chem. Mat. 16,762 (2004).  
  • Organizing Carbon Nanotubes with Liquid Crystal Solvents, M. Lynch, D. L. Patrick, Nanolett., 21197 (2002).