Towards Surface Science Studies of Surfaces Formed by Molecular Assemblies Using Scanning Tunneling Microscopy

Abstract

The adsorption of molecules on surfaces are the central issues for classical surface science studies since the beginning of this important field. It could be noted that the fundamental investigations have been dedicated to the surfaces of metals, semiconductors and oxides which have great implications in catalysis, microelectronic devices etc. With the fast evolving research field of constructing molecular architectures with expectations on various functions, the knowledge at single molecule level on the interacting mechanisms are keenly needed. The development of the molecular nanostructures has also ushered in an interesting studying topic relating to the interfaces between dissimilar molecular species. Studies on heterogeneous molecular interfaces could have multiple implications from understanding of fundamental aspects of inter-molecular interactions, to the working mechanisms of molecular devices. This category of studies could also form a natural extension of the classical surface science principles for metals, semiconductors and oxides. To this aspect, scanning tunnelling microscopy (STM), with the demonstrated resolution capability at single molecule level, could provide unique approaches to reveal interactions between dissimilar molecules. Numerous STM studies have helped gain important insight on the interactions among dissimilar molecules adsorbed on supporting surfaces, such as those in the molecular assemblies prepared under various conditions. In a less noted aspect, the STM can also provide direct evidence on the molecular adsorptions occurred on top of the close packed molecular layers serving as the support surfaces in the way exactly as traditional pristine surfaces of metals, semiconductors and oxides. The experimental foundations enabling such studies are due to the known STM resolution capability within one nanometer or so in the surface normal direction on conductive surfaces. This detection range is well suited for construction of two or even more molecular layers of similar or dissimilar species on top of the support conducting solid surfaces. From molecular adsorption’s perspective, the similarities of the investigations on such molecular surfaces with traditional solid surfaces are