Defect-induced states in the electronic structure of a Cu(100)-benzenethiolate-pentacene heterostructure

We report on the influence of defects in the electronic properties of a pentacene single-layer grown on a benzenethiolate self-assembled-monolayer (Bt-SAM) adsorbed on Cu(100) at 300 K, using high-resolution ultraviolet photoelectron spectroscopy. The weak interaction between pentacene and the underlying Bt-SAM is deduced by the lineshape and evolution of the highest-occupied molecular orbital (HOMO). Closer inspection of the pentacene HOMO band reveals a skewed feature, where the contribution in the low binding energy side is found originating from states associated to structural defects that can be reduced by controlled mild-temperature annealing (355 K). Presence of such defects influences also the pentacene HOMO onset energy and hole-injection barrier that can be reduced to typical value of this organic heterostructure after the annealing. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2986157]