Experimental Studies on the Structure and Interfacial Electronic Structure of Organic Ultrathin Films on Inorganic Solid Surfaces

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Recently, there has been much attention on the structure and functionality of organic ultrathin films on the surface of inorganic solidsk, in relation to various applications such as molecular devices and liquid crystal display devices. Much part of such functions depend on the structure of the thin films at the very interface, and the interfacial electronic structure is important for the electronic functions. There have been studies of structure and moleculra orientation of such films. On the other hand, the interfacial electronic structures have been mostly studied only through macroscopic measurements such as current-voltage characteristics. In this work, we constructed a new apparatus for directly determining the interfacial electronic structures by UV photoemission spectroscopy (UPS), with auxiliary techniuqes for estimating the structures such as Penning ionization electron spetroscopy (PIES). Measurements with this apparatus and also with the UPS system at Institute for Molecular Science using synchrotron radiation, we determined the electronic structures of several eletronically interesting organic solids and interfaces. The systems studied include : polysilanes and polygermanes, silacubane, alminoquinoline, p-sexiphenyl, polypyridine, poly (bipyridine), interfaces between merocyaine dyes and silver halides, and interfaces between porphyrins and metals (Au, Ag, Cu, and Al). The study of dye/silver halide interfaces showed excellent correlation with the actual sensitizing behavior of dyes, strongly supporting the electron transfer mechanism of spectral sensitization by dyes. The results of porphyrin/metal interfaces cast doubt on the traditional simple models, pointing out the importance of more extensive studies of organic/inorganic interfaces.