Thin films of organic molecular crystals (OMCs) have drawn widespread attention for their scientifically interesting and potentially useful properties, with applications ranging from mechanically flexible circuitry, to inexpensive photovoltaics, light emitting diodes, and chemical sensors. However because the properties of OMCs are extremely sensitive to structural imperfections, domain size, and crystallographic orientation, preparation of high quality thin films with controlled microstructural organization under technologically favorable conditions has long been a bottleneck toward practical applications and better controlled fundamental studies. The proposed research will investigate a new approach for fabricating OMC films called organic vapor-liquid-solid (OVLS) deposition. OVLS combines aspects of vapor-phase deposition with solution-phase growth using a liquid or liquid crystalline matrix, offering several advantages compared to conventional physical vapor deposition techniques. These include the ability to perform deposition at ambient pressure and temperature, compatibility with a wide range of molecular building blocks and solvent chemistries, and the ability to exert greater control over growth habit, film morphology, and crystallographic orientation. In short, OVLS deposition has the potential for improved control over several of the most important film growth variables while at the same time operating under conditions favorable for technological exploitation and basic understanding of nucleation and growth. This research, supported by the Solid State and Materials Chemistry program at NSF, will study OVLS deposition to develop a more detailed fundamental understanding of nucleation and growth mechanisms in organic materials and apply that understanding to explore device applications, while providing hands-on introduction to scientific research for 10-15 undergraduate chemistry and physics majors.
NON-TECHNICAL SUMMARY
Molecular crystals are important for many applications, from pharmaceuticals to plastic electronics. For example, in plastic semiconductors - carbon-based molecules that are being actively researched as potential lower-cost replacements for silicon electronics - electrical conductivity depends on how the molecules pack together in crystals, the shapes and sizes of the crystals, and other structural details. Consequently, better control over crystal structure could someday lead to improved electronic devices. Additionally, one would like to be able to grow and control crystallization using low-cost processing techniques, which means transitioning from high vacuum, high temperature methods used today to less severe ambient conditions of pressure and temperature. This research, supported by the Solid State and Materials Chemistry program at NSF, is aimed at developing such methods, and at using them to perform fundamental scientific studies of crystal growth and structure, while investigating their possible application in electronic devices like plastic transistors. The research will also provide hands-on training in advanced materials and scientific research to 10- 15 undergraduates, helping inspire and prepare a future generation of scientists.
