Metallophthalocyanine thin films: Structure and physical properties

Organic semiconductors represent a class of carbon-based compounds with a tremendous potential to exhibit novel physical properties, and to be used in new and important applications. They display different properties compared to their inorganic counterparts, and present many advantages such as unlimited potential to be synthesized in new molecular structures, and capability of being processed inexpensively. Metallophthalocyanines (MPc) belong to the small-molecule group of organic semiconductors, and represent a model system for the whole class of flat, organic molecules. This dissertation presents a study of the structure and the electrical and magnetic properties of thin phthalocyanine films and phthalocyanine-based devices. Chapter one gives an introduction to the general properties of organic semiconductors and the wide range of their physical properties. In particular, the metallophtalocyanines are introduced as being a model system for the small-molecule group of organic semiconductors. Metallophthalocyanines are very well suited to be grown in thin films using organic molecular beam deposition (OMBD) techniques. Chapter two discusses the fabrication of thin phthalocyanine films and devices using OMBD, and the study of their structural properties using a wide range of experimental methods. The molecular shape anisotropy, combined with the interplay between intermolecular and the molecule-substrate interactions, determine different thin film structures that can be controlled by the fabrication conditions. The structure of phthalocyanine thin films determines their electrical transport properties. Chapter three investigates the electrical transport properties of hybrid metal-organic sandwich devices. These properties are controlled not only by the organic film, but also by the metal-organic interfaces. It was found that the low- voltage regime is linear, i.e. Ohmic, for a wide range of temperatures and organic layer thicknesses. The conductance increases exponentially with the temperature and decreases exponentially with the thickness. This behavior was explained with a model that incorporates tunneling between localized states with thermally-induced overlap. Chapter 4 studies the magnetic properties of MPcs. They are controlled by the central metal ion, and the type of molecular stacking in thin films, and were studied using DC magnetometry and magneto-optical techniques. Experimental data suggest the existence of two different magnetic regimes as a function of temperature