From Growth to Electronic Structure of Dipolar Organic Semiconductors on Coinage Metal Surfaces

Abstract

In this thesis, I present a comprehensive study of the interfacial electronic structure and thin film growth of two types of dipolar organic semiconductors on noble metals by employing a surface science approach, which underlines the critical role of surface electronic states in determining the interfacial electronic structure and self-assembly of organic semiconductors. I show that the electronic structure at organic/metal interfaces is complex and depends on important factors such as molecular adsorption configuration, surface/molecule coupling strength, reactivity of the substrate, molecular electrostatics, and local film structure. I demonstrate the fundamental capability of the image potential states and resonances in probing the local film environment, especially in systems consisting of inhomogeneous film structure. I also show that the presence of adsorbates on a surface allows one to investigate quantum mechanical interference effects otherwise not accessible on the bare surface. The dipolar organic semiconductors studied here are vanadyl naphthalocyanine (VONc) and chloroboron-subphthalocyanine (ClB-SubPc). The single crystals of gold and copper with hexagonal surface symmetry (111) were used to investigate the interfacial properties of VONc and ClB-SubPc, respectively. The fundamental understanding of self-assembly of large π-conjugated organic semiconductors on metals is a crucial step in controlling fabrication of supramolecular structures. Here, I provide a first step in this direction with a detailed and quantitative analysis of molecular nearest-neighbor distances that unravels the fundamental intermolecular interactions of organic semiconductors on transition metal surfaces. I additionally investigated the interfacial electronic structure of these organic semiconductors to examine the relation between molecular adsorption orientation and charge transfer across the interface.