title: Sub-wavelength modulation of χ(2)optical nonlinearity in organic thin films.
abstract: Modulating the second-order nonlinear optical susceptibility (χ(2)) of materials at the nanoscale represents an ongoing technological challenge for a variety of integrated frequency conversion and nonlinear nanophotonic applications. Here we exploit the large hyperpolarizability of intermolecular charge transfer states, naturally aligned at an organic semiconductor donor-acceptor (DA) interface, as a means to control the magnitude and sign of χ(2)at the nanoscale. Focusing initially on a single pentacene-C60DA interface, we confirm that the charge transfer transition is strongly aligned orthogonal to the heterojunction and find that it is responsible for a large interfacial nonlinearity probed via second harmonic generation that is sufficient to achieve d33>10 pm V-1, when incorporated in a non-centrosymmetric DA multilayer stack. Using grating-shadowed oblique-angle deposition to laterally structure the DA interface distribution in such multilayers subsequently enables the demonstration of a χ(2)grating with 280 nm periodicity, which is the shortest reported to date.
authors.affiliation: Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: Yixin
authors.initials: Y
authors.lastname: Yan
authors.affiliation: Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: Yakun
authors.initials: Y
authors.lastname: Yuan
authors.affiliation: Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: Baomin
authors.initials: B
authors.lastname: Wang
authors.affiliation: Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: Venkatraman
authors.initials: V
authors.lastname: Gopalan
authors.affiliation: Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: Noel C
authors.identifier: 0000-0002-3798-5830
authors.initials: NC
authors.lastname: Giebink