Supramolecular Assembly of In-Plane Organic Crystals via Solvent-Vapor Exposure

The exceptional electronic and optical properties of high-quality organic crystals are well known and have been exploited in active electronic and optoelectronic devices such as field-effect transistors, photodetectors and optical modulators. This paper describes a room temperature method for in-plane growth of organic crystal needles from initially amorphous thin films of the molecular organic semiconductor tris(8-hydroxyquinoline)aluminum (Alq3). Vacuum-deposited Alq3 films are exposed to methanol vapor at room temperature and pressure, yielding submicron-thick needles with typical in-plane dimensions of several microns wide by tens of microns long. This paper presents characterization results and discusses the mechanisms of crystal growth.