Abstract
One of the fundamental requirements in the development of silicon-based molecular electronic devices is the ability to attach organic molecules to silicon surfaces to form well-defined structures that are stable and possess specific characteristics. Previous work has shown that, although norbornadiene (NBE) forms very stable structures on the Si(001) surface with its apex CH2 group pointing outward from the surface, these structures cannot be resolved in scanning tunneling microscopy. In this paper, we report the results of density functional theory calculations of the interaction with the Si(001) surface of 7-trifluoroacetoxy-norbornadiene (7-TFA-NBE) in which a hydrogen atom of the apex CH2 group is substituted by the trifluoroacetoxy OC(O)CF3 group. This molecule is shown to form very stable structures with the trifluoroacetoxy group sitting well above the surface. Moreover, in contrast to NBE, we find that the different 7-TFA-NBE chemisorption structures should be distinguishable in high-resolution scanning tunneling microscopy experiments. This raises the exciting possibility of employing norbornadiene-based molecules with appropriately chosen functional groups to create molecular structures on Si(001) that are stable and experimentally distinguishable and yield the requisite atomic and electronic properties.