Interface Properties of Organic parapara-Hexaphenyl/α-Sexithiophene Heterostructures Deposited on Highly Oriented Pyrolytic Graphite

It was recently reported, that heterostructures of para hexaphenyl p 6P and amp; 945; sexithiophene 6T deposited on muscovite mica exhibit the intriguing possibility to prepare lasing nanofibers of tunable emission wavelength. For p 6P 6T heterostructures, two different types of 6T emission have been observed, namely, the well known red emission of bulk 6T crystals and additionally a green emission connected to the interface between p 6P and 6T. In this study, the origin of the green fluorescence is investigated by photoelectron spectroscopy PES . As a prerequisite, it is necessary to prepare structurally similar organic crystals on a conductive surface, which leads to the choice of highly oriented pyrolytic graphite HOPG as a substrate. The similarity between p 6P 6T heterostructures on muscovite mica and on HOPG is evidenced by X ray diffraction XRD , scanning force microscopy SFM , and optical spectroscopy. PES measurements show that the interface between p 6P and 6T crystals is sharp on a molecular level without any sign of interface dipole formation or chemical interaction between the molecules. We therefore conclude that the different emission colors of the two 6T phases are caused by different types of molecular aggregatio