Energy band and vacuum level alignment at a semiconductor-molecule-metal interface

We calculated the atomic structure and energy-level alignment at a representative Si-molecule-metal interface. The covalently bonded Si-molecule interface largely determines the overall band offset and the highest occupied molecular orbital position, while charge transfer across the metal-molecule interface induces localized pi levels, even in the absence of covalent bonding to the metal. We propose a scheme for the vacuum level adjustment, consistent with the formation of interfacial dipoles and charge transfer to the molecular layer. The highest occupied pi level of the molecule should be the main electronic state involved in the transport properties, while interface dipoles appear to be related to the interface-induced states. (C) 2008 American Institute of Physics.