Coverage-Dependent Modification of the Surface Electronic Structure of an Organic-Semiconductor-Adsorbate Layer

The electronic structure of a hexa-cata-hexabenzocoronene (HBC)/Cu(111) interface is investigated by two-photon photoemission over a range of coverage from 0 to 2 ML monolayers. It is found that increasing the HBC coverage shifts the vacuum level of the Cu substrate until this shift saturates at a coverage of ∼2 ML. Over this same range of coverage, the Shockley and the bare-surface Cu(111) image-potential states are shown to be quenched, while new unoccupied states appear and grow in strength with coverage. The use of momentum- and polarization-resolved photoemission spectra reveals that the new states are modified image states.