Quantum confinement and anisotropy in thin-film molecular semiconductors

Unoccupied electronic states are probed in epitaxial films of metal phthalocyanines on Ag(111) using angle-resolved two-photon photoemission spectroscopy. Quantum confinement of an image state wave function results in band folding and the opening of a band gap. Angle-resolved photoemission intensity measurements resolve the probability density of the wave function, and are able to identify the symmetry of each band. These results are compared with predictions from a two-dimensional scattering model, and they point to the importance of the spatial extent and symmetry of functional groups in predicting and controlling electronic structure on surfaces and in molecular thin films.