Molecules on Si: Electronics with chemistry

Basic scientific interest in using a semiconducting electrode in moleculebased electronics arises from the rich electrostatic landscape presented by semiconductor interfaces. Technological interest rests on the promise that combining existing semiconductor (primarily Si) electronics with (mostly organic) molecules will result in a whole that is larger than the sum of its parts. Such a hybrid approach appears presently particularly relevant for sensors and photovoltaics. Semiconductors, especially Si, present an important experimental test-bed for assessing electronic transport behavior of molecules, because they allow varying the critical interface energetics without, to a first approximation, altering the interfacial chemistry. To investigate semiconductor-molecule electronics we need reproducible, high-yield preparations of samples that allow reliable and reproducible data collection. Only in that way can we explore how the molecule/electrode interfaces affect or even dictate charge transport, which may then provide a basis for models with predictive power. To consider these issues and questions we will, in this Progress Report, o review junctions based on direct bonding of molecules to oxide-fřee Si. o describe the possible charge transport mechanisms across such interfaces and evaluate in how far they can be quantified, o investigate to what extent imperfections in the monolayer are important for transport across the monolayer, o revisit the concept of energy levels in such hybrid systems.