Structural and electronic properties of single molecules and organic layers on surfaces

Abstract

Single molecules and organic layers on well-defined solid surfaces have attracted tremendous attention owing to their interesting physical and chemical properties. The ultimate utility of single molecules or self-assembled monolayers (SAMs) for potential applications is critically dependent on the structural, electronic and dynamic properties. Therefore is it important to study the structural and electronic properties as well as the dynamic processes of single molecules and organic layers on surfaces. Using scanning tunneling microscopy (STM) single molecules or organic layers on surfaces are studied while their electronic and dynamic properties are probed using scanning tunneling spectroscopy (STS). In order to design and realize single-molecule devices it is essential to obtain a good understanding of the properties of an individual molecule. The transport through a single octanethiol molecule trapped between an STM tip and a Pt/Ge(001) substrate is systematically studied. Spatially resolved current-time (I(t)) spectroscopy combined with current-distance (I(z)) spectroscopy has been used to characterize the dynamic behavior of copper-phthalocyanine (CuPc) molecules adsorbed on a Au-modified Ge(001) surface. Also a new approach to measure the spatially resolved thermovoltage in an STM is described. The bulk part of this thesis describes the dynamics of SAMs or single molecules that interact with a surface using different scanning tunneling spectroscopic tools. Deep insights discovered in the dynamics of the SAMs down to the single molecular level were obtained. In addition, the conductance of an octanethiol and the switching frequency of a CuPc molecule can be accurately adjusted by precisely adjusting the tip-molecule distance. The work in this thesis further enhances the knowledge of dynamic processes in SAMs and other molecular systems induced by the interaction with the surface.