Browsing by Author "Therien, MJ"

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    Carrier Dynamics Engineering for High-Performance Electron-Transport-Layer-free Perovskite Photovoltaics
    (CHEM, 2018-10-11) Han, Q; Ding, J; Bai, Y; Li, T; Ma, JY; Chen, YX; Zhou, Y; Liu, J; Ge, QQ; Chen, J; Glass, JT; Therien, MJ; Liu, J; Mitzi, DB; Hu, JS
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    Predicting the frequency dispersion of electronic hyperpolarizabilities on the basis of absorption data and thomas-kuhn sum rules
    (Journal of Physical Chemistry C, 2010-02-11) Hu, X; Xiao, D; Keinan, S; Asselberghs, I; Therien, MJ; Clays, K; Yang, W; Beratan, DN
    Successfully predicting the frequency dispersion of electronic hyperpolarizabilities is an unresolved challenge in materials science and electronic structure theory. We show that the generalized Thomas-Kuhn sum rules, combined with linear absorption data and measured hyperpolarizability at one or two frequencies, may be used to predict the entire frequency-dependent electronic hyperpolarizability spectrum. This treatment includes two- and three-level contributions that arise from the lowest two or three excited electronic state manifolds, enabling us to describe the unusual observed frequency dispersion of the dynamic hyperpolarizability in high oscillator strength M-PZn chromophores, where (porphinato)zinc(II) (PZn) and metal(II)polypyridyl (M) units are connected via an ethyne unit that aligns the high oscillator strength transition dipoles of these components in a head-to-tail arrangement. We show that some of these structures can possess very similar linear absorption spectra yet manifest dramatically different frequency dependent hyperpolarizabilities, because of three-level contributions that result from excited state-to excited state transition dipoles among charge polarized states. Importantly, this approach provides a quantitative scheme to use linear optical absorption spectra and very limited individual hyperpolarizability measurements to predict the entire frequency-dependent nonlinear optical response. Copyright © 2010 American Chemical Society.
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    Probing polarization and dielectric function of molecules with higher order harmonics in scattering-near-field scanning optical microscopy
    (Journal of Applied Physics, 2009-12-28) Nikiforov, MP; Kehr, SC; Park, TH; Milde, P; Zerweck, U; Loppacher, C; Eng, LM; Therien, MJ; Engheta, N; Bonnell, D
    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.