Probing polarization and dielectric function of molecules with higher order harmonics in scattering-near-field scanning optical microscopy

Abstract

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.

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10.1063/1.3245392

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Nikiforov, MP, SC Kehr, TH Park, P Milde, U Zerweck, C Loppacher, LM Eng, MJ Therien, 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(11). p. 114307. 10.1063/1.3245392 Retrieved from https://hdl.handle.net/10161/3353.

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Therien

Michael J. Therien

William R. Kenan, Jr. Distinguished Professor of Chemistry

Our research involves the synthesis of compounds, supermolecular assemblies, nano-scale objects, and electronic materials with unusual ground-and excited-state characteristics, and interrogating these structures using state-of-the-art transient optical, spectroscopic, photophysical, and electrochemical methods. Research activities span physical inorganic chemistry, physical organic chemistry, synthetic chemistry, bioinorganic chemistry, spectroscopy, photophysics, excited-state dynamics, spintronics, and imaging. My laboratory: (i) designs chromophores and supermolecules that display exceptional opto-electronic properties and elucidates their excited-state dynamics, (ii) engineers highly conjugated molecular structures for optical limiting, specialized emission, and high charge mobility, (iii) designs conjugated materials and hybrid molecular-nanoscale structures for energy conversion reactions, (iv) develops molecular wires that propagate spin-polarized currents, (v) fabricates emissive nanoscale structures for in vivo optical imaging, (vi) engineers de novo transition metal cofactor-binding proteins that test light-driven biological energy transducing mechanisms and realize opto-electronic functionalities not found in nature, and (vii) designs and interrogates complex molecular and nanoscale assemblies in which ultrafast energy and charge migration reactions are controlled by quantum coherence effects.


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