Bulletin of the American Physical Society
2016 Fall Meeting of the APS Ohio-Region Section
Volume 61, Number 12
Friday–Saturday, October 7–8, 2016; Bowling Green, Ohio
Session C3: Photonics, Nanoscience and Photochemistry I |
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Chair: Natalia Razgoniaeva, Bowling Green State University Room: 202 |
Saturday, October 8, 2016 9:30AM - 9:42AM |
C3.00001: Simultaneous Spectroscopic and Topographic Imaging of Single-Molecule Interfacial Electron Transfer Reactivity and Local Nanoscale Environment Yufan He, Vishal Rao, Jin Cao, Peter Lu The fundamental information related to the energy flow between molecules and substrate surfaces as a function of surface site geometry and molecular structure are critical for understanding interfacial electron transfer (ET) dynamics. The inhomogeneous nanoscale molecule-surface and molecule-molecule interactions are presumably the origins of the complexity in interfacial ET dynamics, thus, identifying the environment of molecules at nanoscale is crucial. We have developed AFM correlated single-molecule fluorescence intensity/lifetime imaging microscopy (AFM-SMFLIM) capable of identifying and characterizing individual molecules distributed across the heterogeneous surface at nanometer length scale. Using the combined AFM-SMFLIM imaging, we are able to obtain nanoscale morphology and interfacial ET dynamics at single-molecule level. Moreover, the correlated information about the fluorescence blinking behavior of each individual dye molecule and its lifetime along with the local nano scale topography explains the inhomogeneity of coupling strength of each dye with TiO2 NPs and its effect on interfacial electron transfer reactivity intermittency. The molecular-level understanding of the interfacial ET reactivity, derived from our study, sheds light on the intrinsic fluctuating and inhomogeneous interfacial ET dynamics, which may, for example, help on the development of solar energy conversion science and photocatalysis. ( J. Phys. Chem. Lett., 7,2221-2227(2016)) [Preview Abstract] |
Saturday, October 8, 2016 9:42AM - 9:54AM |
C3.00002: Hot-injection Colloidal Synthesis and Characterization of Nanocrystalline Marcasite Iron Ditelluride {FeTe}$_{\mathrm{\mathbf{2}}}$ Ebin Bastola, Khagendra Bhandari, Randy Ellingson Colloidal semiconductor nanocrystalline (NC) materials are promising functional materials for advanced opto-electronic applications. Iron dichalcogenide nanocrystals such as iron pyrite (FeS$_{\mathrm{2}})$ have been successfully applied as hole transport material to enhance the performance of solar cells. Here, we report a hot-injection colloidal synthesis of NC iron ditelluride (FeTe$_{\mathrm{2}})$ using iron (II) bromide as an iron source and elemental tellurium (Te). The synthesized NC FeTe$_{\mathrm{2}}$ are characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM) imaging, energy dispersive X-ray spectroscopy (EDS), and Raman spectroscopy. These NC FeTe$_{\mathrm{2}}$ exhibit orthorhombic crystal structure in marcasite phase. The SEM images show irregular shape and size, and based on the EDS analysis, the average atomic ratio of tellurium (Te) to iron (Fe) is 2.04. Additionally, we discuss optical and electronic properties of thin films of these as-synthesized NC FeTe$_{\mathrm{2}}$ and its possible application. [Preview Abstract] |
Saturday, October 8, 2016 9:54AM - 10:06AM |
C3.00003: Colloidal Synthesis of Monodisperse Semiconductor Nanocrystals through the Saturated Ionic Layer Adsorption. Natalia Razgoniaeva We demonstrate a general strategy for the synthesis of colloidal semiconductor nanocrystals (NCs) exhibiting the size dispersion below 5{\%}. The present approach relies on the sequential deposition of fully saturated cationic and anionic monolayers onto small-diameter clusters, which leads to focusing of nanocrystal sizes with the increasing particle diameter. Each ionic layer is grown through a room-temperature colloidal atomic layer deposition (ALD) process that employs a two-solvent mixture to separate the precursor and nanocrystal phases. As a result, unreacted precursors can be removed after each deposition cycle, preventing the secondary nucleation. By using CdS NCs as a model system, we demonstrate that a narrow size dispersion can be achieved through a sequential growth of Cd$^{2+}$ and S$^{2-}$ layers onto starting CdS cluster ``seeds''. Besides shape uniformity, the demonstrated methodology offers an excellent batch-to-batch reproducibility and an improved control over the nanocrystal surface stoichiometry. The present synthesis is amenable to other types of semiconductor nanocrystals and can potentially offer a viable alternative to traditional hot-injection strategies of the nanoparticle growth. [Preview Abstract] |
Saturday, October 8, 2016 10:06AM - 10:18AM |
C3.00004: What Controls the Size of Silver Glutathionate Molecular Nanoparticles During Their Formation? Yeakub Zaker, Nathan Diemler, Brian Ashenfelter, Anil Desireddy, Badri Bhattarai, Terry Bigioni Size control remains a longstanding challenge in the production of molecular metal nanoparticles. For example, the silver:glutathione (Ag:SG) system is known to produce \textgreater 20 different discrete molecular species, therefore isolation of any particular size requires size fractionation of the mixed-size products. It is possible to obtain singular Ag:SG nanoparticle products by attrition, i.e. destroying all but the desired product, but this is a laborious procedure with low yield. Here, we present a methodology for producing nearly single-sized products of Ag:SG molecular nanoparticles directly, with no post-processing required, with good yield. By studying the consequences of different reaction conditions on the size distribution, the effects of reduction rate, pH, buffer composition, temperature, time, and precursor solubility could be disentangled. The rate of the reaction was found to have the most significant effect, with slower reaction rates producing small sizes and the narrowest distributions. These results were used to develop a facile method for producing Ag$_{\mathrm{15}}$(SG)$_{\mathrm{11}}$ and Ag$_{\mathrm{32}}$(SG)$_{\mathrm{19}}$ in high yield. [Preview Abstract] |
Saturday, October 8, 2016 10:18AM - 10:30AM |
C3.00005: Electronic Properties of Graphene Nanoribbons Using Extended H\"{u}ckel Theory Spencer Jones, Mahfuza Khatun We will present results of electronic properties of armchair and zigzag graphene nanoribbons (GNRs) calculated with extended H\"{u}ckel (EHT) theory. Energy band structures and density of states (DOS) are calculated using a tight-binding TB model, and Green's function method and the Landauer formula have been implemented determining the transmission function, conductance, and local density of states (LDOS). We have investigated the effects of edge states of the ribbons where edge atoms are terminated with hydrogen atom. Results of without- and with- edge terminated structures have been studied near the Fermi level. The interesting observation is the effect of the dangling bonds at the edges. The EHT technique not only includes the Pz orbital interactions but also the other three S, Px, and Py orbital interactions We observe that there is no fundamental difference in the electronic properties near the Fermi energy for the edge terminated GNRs. The only difference between the two methods is in the conduction and valence band regions away from the Fermi level. We expect the characteristics of electronic properties will be different if the edges are terminated with heavy element (s). [Preview Abstract] |
Saturday, October 8, 2016 10:30AM - 10:42AM |
C3.00006: Thinking Green with Molecular Silver Nanoparticle Production Badri Bhattarai, Indranath Chakraborty, Brian Conn, Aydar Atnagulov, Thalappil Pradeep, Terry Bigioni Solution-phase (NP) syntheses involve large amounts of solvent and produce small quantities of product. Although dry methods of making NPs exist (e.g. ball milling), for ligand-passivated colloidal NPs the costs (financial, environmental, health, etc.) associated with solvent use seem to be inevitable. A partially solid-state synthesis was recently proposed wherein the amount of solvent was significantly reduced, however it was not well developed and lacked generality. We have studied this process to understand the limits of the solid-state approach and to leverage the best features of both solid-state and liquid-state approaches. Most importantly, we used a silver-thiolate paste as a precursor, instead of a metal salt solution, to achieve intimate mixing of solid-state reagents, eliminate solvent waste, and retain the high mobility needed for a high yield reaction. The synthesis yielded solid NPs, in paste form, which may be processed using a nominal quantity of solvent. This produced only Na$_{\mathrm{4}}$Ag$_{\mathrm{44}}(p$-MBA)$_{\mathrm{30}}$ NPs with an 89{\%} yield and reduced solvent use by \textasciitilde 90{\%}. [Preview Abstract] |
Saturday, October 8, 2016 10:42AM - 10:54AM |
C3.00007: Relationship between HOMO-LUMO gap and stability of noble metal molecular nanoparticles (MNPs) in gas and condensed phases Aydar Atnagulov, Sameera Wickramasinghe, Terry Bigioni The energy difference between the highest occupied and lowest unoccupied molecular orbitals, the HOMO-LUMO gap, is often used to rationalize the stability of noble gas atoms, transition metal complexes, and gas phase metal clusters. In the latter case, electrons delocalized across the metal atoms occupy orbitals that are analogous to atomic orbitals such that the cluster may be treated as a ``superatom''. In the gas phase, it has been shown that bare metal clusters with closed electronic shells exhibit higher stability compared to those with incomplete shells. In the condensed phase, the HOMO-LUMO gap has also been adopted to characterize the expected stability of ligand-protected clusters, but the extent to which this is correct remains untested. Here, we address the relationship between HOMO-LUMO gap and gas and condensed phase stabilities using a binary system of M3Ag17(TBBT)12 and M4Ag44(TBBT)30, where TBBT is 4-tert-butylbenzenethiol and M is an alkali metal. Gas phase stabilities of these nanoparticles were evaluated by measuring their fragmentation using mass spectrometry. Condensed phase stabilities were evaluated by analyzing the composition of solutions at different time points. We found that the HOMO-LUMO gap correlated with gas phase stability, but the cluster with the smaller HOMO-LUMO gap was more stable in solution. This implies that the notion of an energy gap fails to predict stability in the condensed phase. [Preview Abstract] |
Saturday, October 8, 2016 10:54AM - 11:06AM |
C3.00008: Enhanced Photoconversion Efficiency in CH$_{\mathrm{3}}$NH$_{\mathrm{3}}$PbI$_{\mathrm{3\thinspace }}$Solar Cells with Cadmium Incorporation Suneth Watthage, Zhaoning Song, Niraj Shrestha, Adam Phillips, Geethika Liyanage, Paul Roland, Randy Ellingson, Michael Heben Non-radiative recombination is the primary energy loss in organic-inorganic metal halide perovskites solar cells, which significantly reduces the power conversion efficiency of the devices. To reduce the density of trap states that controls non-radiative recombination, it is important to prepare perovskite films consisting of large-sized grains with a high degree of crystallinity. Here, we show that the addition of small concentrations of Cd2$+$ in the methylammonium iodide precursor solution during the two-step sequential deposition can significantly improve the grain size and crystallinity of methylammonium lead iodide perovskite thin films. The grains are highly oriented in the \textless 110\textgreater direction compare to films produced by the standard two-step deposition, indicating a change in the growth mechanism. Time resolved photoluminescence measurements indicated a dramatic increase in the carrier lifetime which can be attributed to a reduction in the active trap density. Highly reproducible photovoltaic devices were obtained from the Cd-modified perovskites with a 13.8 {\%} device efficiency, while only 7.1 {\%} PCE was obtained from the standard two-step process. [Preview Abstract] |
Saturday, October 8, 2016 11:06AM - 11:18AM |
C3.00009: Electronic Coupling--Decoupling-Dependent Single-Molecule Interfacial Electron Transfer Dynamics in Electrostatically Attached Porphyrin on TiO$_{\mathrm{2}}$ Nanoparticles B. Dhital, V. Govind Rao, H. P. Lu Interfacial electron transfer (ET) is of crucial importance in a multitude of chemical and physical applications including solar energy conversion and photocatalytic reactions. Extensive ensemble-averaged studies have indicated complex dynamics involving various regulating parameters for interfacial ET. To characterize the role of electronic coupling in inhomogeneous and complex ET mechanism, we applied photon-stamping spectroscopy to study the interfacial ET dynamics of single cationic dyes electrostatically attached on the surface of TiO$_{\mathrm{2}}$ nanoparticles (NPs). By changing the surface charge on the TiO$_{\mathrm{2}}$ NP, positive or negative, we were able to change the coupling between dye and TiO$_{\mathrm{2}}$ NP. The interfacial ET activity of individual molecules altered depending on the electronic coupling strength between dye and TiO$_{\mathrm{2}}$ NP. Our data showed high ET activity of cationic dyes attached on negatively charged TiO$_{\mathrm{2}}$ NP surface compared to positively charged TiO$_{\mathrm{2}}$ NP surface. The observed difference in ET activity attributed to the change in purely electronic coupling factor via electrostatic interaction. Thus, our real-time single molecule experiment revealed the significant changes in ET activity with electronic coupling for electrostatically attached dyes on TiO$_{\mathrm{2\thinspace }}$surface.[\textit{J. Phys. Chem.} C \textbf{2016}, \textit{120}, 12313] [Preview Abstract] |
Saturday, October 8, 2016 11:18AM - 11:30AM |
C3.00010: Translationally Invariant Local One-Body Densities for $^6$He Matthew Burrows, Charlotte Elster, Gabriela Popa Applications of No-Core-Shell-Model (NCSM) densities in reaction calculations require that they are translationally invariant. In order to obtain translationally invariant local one-body densities for $^6$He we first reconstruct them in a space-fixed, coordinate-space frame from the output of NCSM calculation. Then the center-of-mass contribution is removed exactly in momentum-space. Space-fixed and translationally invariant densities are compared. RMS radii are computed from the translationally invariant local densities. [Preview Abstract] |
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