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November 2018
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  1. CFN Colloquium

    4 pm, Bldg 735, Seminar Room, 2nd Floor

    Hosted by: Mircea Cotlet

    Metal halide perovskites have drawn significant attention because of their ability to deliver high efficiency solar cells. Mixed halide lead perovskites offer a useful strategy for continuous tuning of the semiconductor bandgap. For example, by varying the halide ion composition of methylammonium lead iodide/bromide (CH3NH3PbBr¬xI3-x (x=0 to 3)) it is possible to tune the bandgap between 1.55 eV and 2.43 eV. In addition to photovoltaic applications these mixed halide perovskites offer rich photophysical properties with applications in lasing and optoelectronic devices. An intriguing property of mixed halide lead perovskites (e.g.,CH3NH3PbI3-xBrx) is phase segregation to create iodide-rich and bromide- rich regions under visible irradiation. The halide ion movement in mixed halide films can be tracked from the changes in the photoluminescence and absorption spectra. Photoinduced segregation in mixed halide perovskite has a direct influence on decreasing the solar cell efficiency as segregated I-rich domains serve as charge recombination centers. The recovery of loss in the external quantum efficiency mirrors the dark recovery of the absorption showing the reversibility of the photoinduced halide segregation. Implication of such halide ion migration in mixed halide perovskite solar cell will be discussed. Related Readings 1. Manser, J. S.; Saidaminov, M. I.; Christians, J. A.; Bakr, O. M.; Kamat, P. V., Making and Breaking of Lead Halide Perovskites. Accounts of Chemical Research 2016, 49, 330-338. 2. Manser, J. S.; Christians, J. A.; Kamat, P. V. Intriguing Optoelectronic Properties of Metal Halide Perovskites. Chem. Rev. 2016, 116, 12956–13008. 3. Hoffman, J. B.; Schleper, A. L.; Kamat, P. V., Transformation of Sintered CsPbBr3 Nanocrystals to Cubic CsPbI3 and Gradient CsPbBrxI3–x through Halide Exchange. J. Am. Chem. Soc. 2016, 138, 8603–8611. 4. Draguta, S.; Sharia, O.

  2. CFNS Seminar

    4 pm, CFNS Seminar Room 2-38

    Hosted by: Andrey Tarasov

    "A graph by graph correspondence between decay probabilities (timelike) and light cone wavefunctions (spacelike) is described in massless (regularized) QCD. This correspondence is broken in unregularized QCD by running coupling effects. Through NLO in soft gluons a Gell Mann-Low type QCD is described where the correspondence remains correct."

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  1. Center for Functional Nanomaterials Seminar

    1 pm, Bldg. 735 conference room A, 1st floor

    Hosted by: Dario Stacchiola

    Department of Chemistry, NIS Centre and INSTM Reference Center, University of Turin, Turin, Italy. University of Oslo, Department of Chemistry, Oslo, Norway. Cu-exchanged chabazite (Cu-CHA) is currently the object of intensive research efforts to rationalize its outstanding performance in the NH3-assisted selective catalytic reduction (SCR) of NOx1 and its recently proved activity in the direct conversion of methane to methanol (MTM).2 Cu is usually introduced into the zeolites via aqueous ion exchange, resulting in the formation of [Cu(OH)]+ and/or Cu2+ counterions. Recent works pointed out that the relative abundance of [Cu(OH)]+ and Cu2+ depends on the Cu/Al and Si/Al ratios, and proposed that only [Cu(OH)]+ can be 'self-reduced' to Cu+ sites during activation in inert atmosphere.3 To shed light on this aspect, which has important implications on the design and understanding of active catalysts for both SCR and MTM reactions, we prepared a large set of Cu-CHA samples with different Cu/Al and Si/Al ratios. These were characterized in situ by X ray Absorption (XAS) and FTIR of adsorbed probe molecules, to follow Cu speciation and evolution during activation in different conditions.4,5 Use of multivariate data-modelling allowed us to access an unprecedented level of understanding in a complex multi-component catalytic system, yielding novel insights into the birth of Cu-active sites in the cages of the CHA zeolite.4 For more details on: "Cu-CHA – a model system for applied selective redox catalysis", see the review by Borfecchia et al. 6 References: 1 Beale, A. M.; Gao, F.; Lezcano-Gonzalez, I.; Peden, C. H. F.; Szanyi, J. Chem Soc Rev 2015, 44, 7371-7405. 2 Wulfers M.J., Teketel, S., Ipek, B., Lobo R. F., Chem. Commun. 2015, 51, 4447-4450. 3 Paolucci, C.; Parekh, A. A.; Khurana, I.; Di Iorio, J. R.; Li, H.; Caballero, J. D. A.; Shih, A. J.; Anggara, T.; Delgass, et al. J Am Chem Soc 201

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  1. DEC

    6

    Thursday

    CFN Colloquium

    "Metamaterial, Metasurface and Plasmonic Optics"

    Presented by David Smith, Duke University

    2 pm, Bldg 735, CFN Seminar Room, 2nd Floor

    Thursday, December 6, 2018, 2:00 pm

    Hosted by: Don Dimarzo / Mircea Cotlet

    In 2000, the demonstration of an artificially structured metamaterial with simultaneously negative permittivity and permeability—or a negative index metamaterial—stimulated widespread interest both in the fundamental properties of metamaterials as well as those of plasmonic materials. This interest has had an impact on virtually every aspect of optics and photonics research and technology. Nanostructured materials have the potential for unique and unprecedent photonic devices relevant to applications such as sensing, imaging, information storage and retrieval, processing, and many more. Our group has focused on several metasurface platforms as a means of investigating and demonstrating key concepts. While structuring of a surface or volume provides an important means of controlling the propagation of light with tremendous precision, the use of plasmonic nanostructures provides the means of actually interacting with the radiative dynamics of emitters and other sources, modifying density of states; enhancing or suppressing stimulated and spontaneous emission; modifying nonlinear scattering and harmonic generation; and so forth. The combination of tools available with metamaterials, metasurfaces and plasmonic materials—while still not yet fully exploited—lead to the opportunity for new inventive photonic devices with improved and flexible performance metrics. In this talk, I will describe our group's efforts in the areas of holographic metamaterials, and the need to go beyond holography for multifunctional optical devices. I will also describe the film-coupled nanoparticle platform we have developed over the years and discuss the capability of field enhancement in nanogaps to impact diverse applications such as lasing; ultrafast and ultrabright light sources; light absorbing surfaces; and controlled emission surfaces.

  2. JAN

    3

    Thursday

    CFN Colloquium

    "TBD"

    Presented by Antonio Mezzacapo, IBM T.J. Watson Research Center

    4 pm, CFN, Bldg 735, 2nd Floor Seminar Room

    Thursday, January 3, 2019, 4:00 pm

    Hosted by: Deyu Lu

    TBD