Highly oriented growth of p-sexiphenyl molecular nanocrystals on rubbed polymethylene surface

Highly oriented nanocrystals of p-sexiphenyl molecules were prepared by thermal evaporation of this material on a rubbed polymethylene surface. The polymethylene thin film, generated on a gold surface by the gold-catalyzed decomposition of diazomethane, was gently rubbed in a fixed direction with a flannelette cloth to serve as the template for alignment, which induced the in-plane orientation as well as flat-lying geometry of the molecules in contact with the surface. Anisotropic growth from the aligned molecules resulted in oriented molecular crystals. Various techniques, including reflection-absorption IR spectroscopy (RAIRS), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, grazing incidence X-ray diffraction, and atomic force microscopy were used to elucidate the structural details at the rubbed polymethylene surfaces and the p-sexiphenyl crystals deposited on it. The polymethylene chains near the surface were markedly aligned after the rubbing action, with the carbon chain backbones aligned parallel to the rubbing direction. p-Sexiphenyl formed nanometer-scale, rodlike molecular crystals, with the long axes of the crystals perpendicular to the rubbing direction. Nevertheless, the molecules in the crystals lay "flat" on the rubbed polymethylene surface, with their long molecular axis parallel to the rubbing direction. Large-scale alignment of highly oriented molecular crystals can be achieved in this manner.