Paper SS-TuP2
MORTON S. TRAUM AWARD FINALIST: Coverage-Dependent Interfacial Electronic Structures of Thiophenol and p-Fluorothiophenol on Cu(111)

Tuesday, October 30, 2012, 6:00 pm, Room Central Hall

Femtosecond two-photon photoemission spectroscopy is used to investigate and compare the interfacial electronic structures of thiophenol and p-fluorothiophenol films on Cu(111) as a function of molecular coverage. A new state is found to emerge as the coverage is increased; simultaneously, the Cu(111) Shockley surface state disappears for both molecular species. This similarity in behavior is shown to originate from spatial lateral confinement of the surface electron. In addition, the change in the workfunction vs. coverage shows that the two thiophenols exhibit almost identical behavior until an inflection point at ~1/3 ML coverage but then subsequently diverge. This divergent behavior is attributed to the changing orientation of the phenyl group with coverage. At a full monolayer, the net change in the workfunction for the two molecules have opposite signs, which can be explained using a quantitative model based on a surface and molecular dipole moments.