Electronic structure of [121]tetramantane-6-thiol on gold and silver surfaces.

The mechanism for electron photoemission of [121]tetramantane and its functionalized compound [121]tetramantane-6-thiol adsorbed on different noble metal surfaces has been investigated by density functional theory calculations. It is found that good chemical bonding between molecules and metal surfaces is a helpful but not a necessary condition for electron photoemission. A lower work function and weaker hybridization between the molecule and the metal could lead to much more efficient electron photoemission. It is observed that, neglecting final state effect, a simple ground state picture cannot result in negative electron affinity for the systems under investigation. Calculations have shown that by exciting an electron in the lowest unoccupied molecular orbital, the highest singly occupied molecular orbital of the molecule can be shifted above the vacuum level, resulting in negative electron affinity and emission of the accumulated electrons.