Understanding The Photoemission Distribution Of Strongly Interacting Two-Dimensional Overlayers

Photoemission tomography (PT), the analysis of the photoemission intensity distribution within the plane wave final-state approximation, is being established as a useful tool for extracting the electronic and geometric structure of weakly interacting organic overlayers. Here we present a simple method for extending PT, which until now has been based on the calculations of isolated molecules. By including the substrate and a damped plane-wave final state, we are able to simulate the photoemission intensity distribution of two-dimensional molecular overlayers with both strong intermolecular and molecule-substrate interactions, here demonstrated for the model system 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) on Cu(100). It is shown that the interaction and hybridization of the lowest unoccupied molecular orbital of PTCDA with substrate states leads to its occupation and the formation of a strongly dispersing intermolecular band, whose experimental magnitude of 1.1 eV and k-space periodicity is well reproduced theoretically.