Metal work-function changes induced by organic adsorbates: A combined experimental and theoretical study

The role of molecular dipole moment, charge transfer, and Pauli repulsion in determining the work-function change (Delta Phi) at organic-metal interfaces has been elucidated by a combined experimental and theoretical study of (CH3S)(2)/Au(111) and CH3S/Au(111). Comparison between experiment and theory allows us to determine the origin of the interface dipole layer for both phases. For CH3S/Au(111), Delta Phi can be ascribed almost entirely to the dipole moment of the CH3S layer. For (CH3S)(2)/Au(111), a Pauli repulsion mechanism occurs. The implications of these results on the interpretation of Delta Phi in the presence of strongly and weakly adsorbed molecules is discussed.