POSTDEPOSITION GROWTH OF A UNIQUELY NANOSTRUCTURED ORGANIC FILM BY VACUUM ANNEALING

The organic red pigment N-di(3,5-xylyl)perylene-3,4:9,10bis(dicarboxim ide) is easily vacuum deposited at ambient substrate temperatures to f orm ordinary looking smooth films. When subsequently annealed in vacuo between approximately 160 and 220-degrees-C, an initially 1000 angstr om uniformly thick film transforms to an extremely dense, random array of discrete, crystalline whiskers, uniformly oriented with their long axes normal to the substrate. Whisker growth occurs at zero supersatu ration ratio (no incident flux) and all film material is conserved. Wh isker cross sectional dimensions are approximately 27x55 nm, lengths 1 -1.5 mum, and areal number densities approximately 50 per square micro n. The high-aspect-ratio whiskers grow purely by surface diffusion to minimum energy binding sites believed to be emergent screw dislocation s on the whisker tips, while the uniform cross sectional shapes reflec t the ratio of surface free energies of the bounding crystal faces. Th e transformation has been followed in situ with reflection absorption IR spectroscopy as a function of time and temperature to obtain a dime nsionless growth parameter. The surface self-diffusion coefficient and surface entropy to free energy ratio are extracted. The pigment whisk ers are readily sputter or vapor-coated to provide conformally coated nanostructure-sized features with metal and semiconductor properties. Vapor coating and annealing of the original pigment films can be done reproducibly in large areas and offer a novel alternative approach to plasma etching and photolithography for producing nanostructured surfa ces with new properties.