title: Pronounced polarization-induced energy level shifts at boundaries of organic semiconductor nanostructures.
abstract: Organic semiconductor devices rely on the movement of charge at and near interfaces, making an understanding of energy level alignment at these boundaries an essential element of optimizing materials for electronic and optoelectronic applications. Here we employ low temperature scanning tunneling microscopy and spectroscopy to investigate a model system: two-dimensional nanostructures of the prototypical organic semiconductor, PTCDA (3,4,9,10-perylenetetracarboxylic dianhydride) adsorbed on NaCl (2 ML)/Ag(111). Pixel-by-pixel scanning tunneling spectroscopy allows mapping of occupied and unoccupied electronic states across these nanoislands with sub-molecular spatial resolution, revealing strong electronic differences between molecules at the edges and those in the centre, with energy level shifts of up to 400 meV. We attribute this to the change in electrostatic environment at the boundaries of clusters, namely via polarization of neighbouring molecules. The observation of these strong shifts illustrates a crucial issue: interfacial energy level alignment can differ substantially from the bulk electronic structure in organic materials.
authors.affiliation: Department of Chemistry, University of British Columbia, Vancouver British Columbia, Canada V6T 1Z1.
authors.forename: K A
authors.initials: KA
authors.lastname: Cochrane
authors.affiliation: Department of Physics and Astronomy, University of British Columbia, Vancouver British Columbia, Canada V6T 1Z1.|Quantum Matter Institute, University of British Columbia, Vancouver British Columbia, Canada V6T 1Z4.
authors.forename: A
authors.initials: A
authors.lastname: Schiffrin
authors.affiliation: Department of Physics and Astronomy, University of British Columbia, Vancouver British Columbia, Canada V6T 1Z1.
authors.forename: T S
authors.initials: TS
authors.lastname: Roussy
authors.affiliation: Department of Physics and Astronomy, University of British Columbia, Vancouver British Columbia, Canada V6T 1Z1.
authors.forename: M
authors.initials: M
authors.lastname: Capsoni
authors.affiliation: Department of Chemistry, University of British Columbia, Vancouver British Columbia, Canada V6T 1Z1.|Department of Physics and Astronomy, University of British Columbia, Vancouver British Columbia, Canada V6T 1Z1.|Quantum Matter Institute, University of British Columbia, Vancouver British Columbia, Canada V6T 1Z4.
authors.forename: S A
authors.identifier: http://orcid.org/0000-0002-7337-0569
authors.initials: SA
authors.lastname: Burke