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We study the molecular structure of one monolayer of picene on a Ag(100) surface. Low energy electron diffraction and scanning tunneling microscopy experiments show that the molecules arrange in a highly ordered manner exhibiting a point-on-line epitaxy with two differently arranged molecules per unit cell. Comparing measured and simulated photoelectron momentum maps allows further conclusions about the composition of the unit cell. The structural basis consists of two parallel molecules; one molecule lies face-on and the other is tilted by ≈45° around its long axis with respect to the surface normal.

Herein, we have studied highly ordered two-dimensional layers of 1,2:8,9-dibenzopentacene (trans-DBPen) adsorbed on a single-crystalline silver surface. While its parent molecule pentacene is known for a relatively high hole mobility, reports on trans-DBPen are rather scarce. Furthermore, it belongs to polycyclic aromatic hydrocarbons for which superconducting properties have been observed upon intercalation with potassium. Our scanning tunneling microscopy and low-energy electron diffraction results reveal a highly ordered monolayer structure of trans-DBPen on Ag(111). We further used angle-resolved ultraviolet photoelectron spectroscopy to measure photoelectron momentum maps (PMMs). The experimental PMMs agree very nicely with simulations based on our structural data while assuming free molecules for the density functional theory calculations. A comparison with pentacene yields some insights into the properties of the two related molecules. We conclude that the degree of hybridization between the molecular orbitals and substrate states is comparatively weak. These results are expected to serve as a starting point for future investigations of K-doped monolayers of trans-DBPen.