Probing high quality pentacene monolayers by optical methods

We report optical studies of pentacene monolayers grown on poly-alpha-methyl-styrene (PAMS) substrates of high uniformity that reaches into the micron length-scale in the lateral dimension. Raman scattering intensities from a two-monolayer pentacene film exhibit large resonance enhancements when incoming and outgoing photon energies overlap the free exciton measured in optical emission. The incoming and outgoing resonance enhancements are of about the same strength. The free exciton optical emission band is sharp and intense, and it blue-shifts by about 85 meV from that of the pentacene single crystal.