Probing Polarization and Dielectric Function of Molecules with Higher Order Harmonics in Scattering-near-field Scanning Optical Microscopy

The idealized system of an atomically flat metallic surface [highly oriented pyrolytic graphite (HOPG)] and an organic monolayer (porphyrin) was used to determine whether the dielectric function and associated properties of thin films can be accessed with scanning–near-field scanning optical microscopy (s-NSOM). Here, we demonstrate the use of harmonics up to fourth order and the polarization dependence of incident light to probe dielectric properties on idealized samples of monolayers of organic molecules on atomically smooth substrates. An analytical treatment of light/ sample interaction using the s-NSOM tip was developed in order to quantify the dielectric properties. The theoretical analysis and numerical modeling, as well as experimental data, demonstrate that higher order harmonic scattering can be used to extract the dielectric properties of materials with tens of nanometer spatial resolution. To date, the third harmonic provides the best lateral resolution(~50 nm) and dielectric constant contrast for a porphyrin film on HOPG. Disciplines Engineering | Materials Science and Engineering Comments Suggested Citation: Nikiforov, M.P., et.al. (2009). "Probing polarization and dielectric function of molecules with higher order harmonics in scattering-near-field scanning optical microscopy." Journal of Applied Physics. 106, 114307. © 2009 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. http://dx.doi.org/10.1063/1.3245392 Author(s) Maxim P. Nikiforov, Susanne C. Kehr, Tae-Hong Park, Peter Milde, Ulrich Zerweck, Christian Loppacher, Lukas M. Eng, Michael J. Therien, Nader Engheta, and Dawn A. Bonnell This journal article is available at ScholarlyCommons: http://repository.upenn.edu/mse_papers/189 Probing polarization and dielectric function of molecules with higher order harmonics in scattering–near-field scanning optical microscopy Maxim P. Nikiforov, Susanne C. Kehr, Tae-Hong Park, Peter Milde, Ulrich Zerweck, Christian Loppacher, Lukas M. Eng, Michael J. Therien, Nader Engheta, and Dawn Bonnell The Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA Institute of Applied Photophysics, Technische Universität Dresden, Dresden, 01069, Germany Department of Physics, University of California, Berkeley, California 94720, USA Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA IM2NP-UMR CNRS 6242 and Aix-Marseille University, F–13397 Marseille Cedex 20, France Department of Chemistry, Duke University, Durham, North Carolina 27708, USA Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA Received 4 February 2009; accepted 19 September 2009; published online 3 December 2009 The idealized system of an atomically flat metallic surface highly oriented pyrolytic graphite HOPG and an organic monolayer porphyrin was used to determine whether the dielectric function and associated properties of thin films can be accessed with scanning–near-field scanning optical microscopy s-NSOM . Here, we demonstrate the use of harmonics up to fourth order and the polarization dependence of incident light to probe dielectric properties on idealized samples of monolayers of organic molecules on atomically smooth substrates. An analytical treatment of light/ sample interaction using the s-NSOM tip was developed in order to quantify the dielectric properties. The theoretical analysis and numerical modeling, as well as experimental data, demonstrate that higher order harmonic scattering can be used to extract the dielectric properties of materials with tens of nanometer spatial resolution. To date, the third harmonic provides the best lateral resolution 50 nm and dielectric constant contrast for a porphyrin film on HOPG. © 2009 American Institute of Physics. doi:10.1063/1.3245392