title: Phonon-mediated electron transport through CaO thin films.
abstract: Scanning tunneling microscopy has developed into a powerful tool for the characterization of conductive surfaces, for which the overlap of tip and sample wave functions determines the image contrast. On insulating layers, as the CaO thin film grown on Mo(001) investigated here, direct overlap between initial and final states is not enabled anymore and electrons are transported via hopping through the conduction-band states of the oxide. Carrier transport is accompanied by strong phonon excitations in this case, imprinting an oscillatory signature on the differential conductance spectra of the system. The phonons show a characteristic spatial dependence and become softer around lattice irregularities in the oxide film, such as dislocation lines.
authors.affiliation: Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany.
authors.forename: Yi
authors.initials: Y
authors.lastname: Cui
authors.affiliation: Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, via Cozzi 53, 20125 Milano, Italy.
authors.forename: Sergio
authors.initials: S
authors.lastname: Tosoni
authors.affiliation: Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany and Ecole Polytechnique Fédérale de Lausanne, Institute of Physics, CH-1015 Lausanne, Switzerland.
authors.forename: Wolf-Dieter
authors.initials: WD
authors.lastname: Schneider
authors.affiliation: Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, via Cozzi 53, 20125 Milano, Italy.
authors.forename: Gianfranco
authors.initials: G
authors.lastname: Pacchioni
authors.affiliation: Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany and Carl von Ossietzky Universität Oldenburg, Institut für Physik, D-26111 Oldenburg, Germany.
authors.forename: Niklas
authors.initials: N
authors.lastname: Nilius
authors.affiliation: Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany.
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Freund