Two-photon photoemission from ex-situ prepared butanethiol SAMs on Au (111)

Abstract Self-assembled monolayers (SAMs) of butanethiol on a Au (111) single crystalline surface in the p × 3 lying-down phase prepared by deposition from solution were studied with two-photon photoemission (2PPE) spectroscopy. The spectra reveal clear signatures of two unoccupied resonance states at energies E  −  E F  = 3.7 eV and 3.9 eV. The low-energy state is assigned to the characteristic σ ∗ -resonance associated with the Au-S bond of the thiolate. The energy of the other resonance state agrees well with an interface state reported before for different alkanethiol SAMs on Au (111) in a standing-up phase. Furthermore the 2PPE data provide indications that the high quality of the ex-situ prepared SAMs support the formation of image potential states.