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Abstract

This thesis examines the novel application of two-photon photoemission to the investigation of interfacial electronic structure between a metal substrate and a thin conjugated polymer film. Experimental considerations of the technique are discussed in detail. Theoretical aspects of employing the technique to study metal/conjugated polymer interfaces are compared to those of other, existing methodologies. Preliminary results from two-photon photoemission studies of poly(3-hexylthiophene) films on Au(111) substrates illustrate the ability of the technique to directly probe unoccupied interfacial states involved in electron transfer. The lowest unoccupied molecular orbital (LUMO) of poly(3-hexylthiophene) is found to lie 2.0eV above the Fermi level of the gold substrate, corresponding to a 0.8eV downward shift of the polymer energy levels upon interface formation. Results also illustrate the high sensitivity of the two-photon photoemission technique for studying these systems. A nearly 5000-fold increase in signal intensity from the polymer compared to the bare metal is attributed to the existence of long-lived excited states in the conjugated polymer.