Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session S26: Focus Session: At the Interface of Molecules and Materials: IV |
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Sponsoring Units: DCP Chair: Bruce Weisman, Rice University Room: 204A |
Thursday, March 5, 2015 8:00AM - 8:36AM |
S26.00001: Variance Spectroscopy: A New Bridge between Ensemble and Single-Particle Studies Invited Speaker: R. Bruce Weisman We have developed a new experimental technique that probes variations in the spectra from small regions of heterogeneous bulk samples resulting from statistical variations in composition. The method is demonstrated using suspensions of single-walled carbon nanotubes (SWCNTs), which contain mixtures of distinct structural species emitting photoluminescence at characteristic short-wave infrared wavelengths. Using dilute SWCNT suspensions, focused excitation beams, multichannel detection, and quick data collection, we capture several thousand emission spectra representing different spatial regions of the sample. The data sets are analyzed to find emission mean and variance values as a function of wavelength. The combined mean and variance spectra contain information unavailable from conventional methods, including the abundances of different emissive species and their relative emission efficiencies. The variance data are also analyzed for correlations between intensity fluctuations at different wavelengths to give novel two-dimensional maps that reveal the spectra of homogeneous sub-populations within heterogeneously broadened bulk spectra. The off-diagonal features in these maps expose spatially correlated concentration variations for nanotubes of different types, which arise from earliest stages of aggregation. Variance spectroscopy should prove a powerful new experimental tool for characterizing nanoparticle samples. [Preview Abstract] |
Thursday, March 5, 2015 8:36AM - 9:12AM |
S26.00002: TBD Invited Speaker: Libai Huang |
Thursday, March 5, 2015 9:12AM - 9:48AM |
S26.00003: Multiphoton Photoemission/Velocity Map Imaging Studies of Single Particle Plasmonics: A New Ultrafast Laser Microscopy Tool for Nanomaterials Invited Speaker: David Nesbitt The ability to look with ultrafast laser microscopy at nanoparticules has lead to an explosion of novel research opportunities in chemistry, physics and engineering. By way of example, this talk will attempt to present recent ``vignettes'' from our group in ultrafast photoelectron studies of novel plasmonic nanomaterials. In particular, scanning photoionization microscopy (SPIM) and dynamics of Au, Ag plasmonic rods, cubes, nanoshells, nanostars, etc) have been investigated at the single nanoparticle level, exploiting ultrafast laser pulses tuned over the nanoparticle plasmon resonance features and monitored by time-resolved, coherent multiphoton electron photoemission and velocity map imaging methods. The focus will be on simple physical pictures that help explain and interpret the underlying chemical physics on the nanoscale level.\\[4pt] In collaboration with Andrej Grubisic, NASA and Jacob Pettine, JILA, University of Colorado. [Preview Abstract] |
Thursday, March 5, 2015 9:48AM - 10:00AM |
S26.00004: Femtosecond nanoplasmonic dephasing of individual silver nanoparticles Richa Mittal, Rachel Glenn, Ilyas Saytashev, Marcos Dantus Localized surface plasmon emission from individual silver nanoparticles and cluster of 100nm silver nanoparticles are probed by 15fs laser pulse replica generated by a pulse shaper. The Fourier transform of the nanoplasmonic coherence oscillations reveals different frequency components, phases, and dephasing rates for each nanoparticle. We find broadly distributed coherence dephasing rates that correspond to the cluster size. Our results provide insight into inhomogenous and homogenous broadening mechanisms in nanoplasmonic spectroscopy. [Preview Abstract] |
Thursday, March 5, 2015 10:00AM - 10:12AM |
S26.00005: Flicker Noise as a Probe of Electronic Interaction at Metal-Organic Interfaces Olgun Adak, Ethan Rosenthal, Jeffery Meisner, Erick Andrade, Abhay Pasupathy, Colin Nuckolls, Mark Hybertsen, Latha Venkataraman Understanding the nature of the charge transport at metal-organic interfaces is fundamental for achieving functional organic electronic devices. The charge transport at such interfaces can be achieved by through-bond and through-space interaction. While through-bond interaction~dominates the electronic coupling in most systems, through-space interaction plays important role when through-bond interaction is suppressed, for example, due to quantum interference. In this talk, we first shed light into the origin of the flicker noise phenomenon in single molecule junctions and show how it can be used to distinguish between through-bond and through-space interaction at metal-organic interfaces using a scanning-tunneling microscope based break junction technique. [Preview Abstract] |
Thursday, March 5, 2015 10:12AM - 10:24AM |
S26.00006: Dynamic Oxidation of Gallium Phosphide Surface Tracked by Near Ambient Pressure XPS Sylwia Ptasinska, Xueqiang Zhang Both from applied and fundamental points of view, it is important that we have a detailed molecular-level understanding of gas-solid interface interactions, especially under operational conditions. Recent progress in \textit{in-situ} instrumentations (e.g., Near Ambient Pressure X-ray Photoelectron Spectroscopy---NAP XPS), has enabled us to explore the physicochemical processes at the gas-solid interface over a varied range of pressures (up to mbar range), bridging the gap in our knowledge of interfacial interactions. Our recent investigations have focused on dissociative adsorption of small gas-phase molecules onto III-V semiconductors, which leads to surface oxidation. In this work, we carried out a pressure- and temperature-dependent study of GaP(111) oxidation in an O$_{\mathrm{2}}$ environment. Dynamic changes in chemical evolutions at the O$_{\mathrm{2}}$/GaP(111) interface were reflected in Ga 2p$_{\mathrm{3/2}}$,$_{\mathrm{\thinspace }}$O 1s, and P 2p spectra. Different oxidation states were observed, involving Ga$_{\mathrm{2}}$O, Ga$_{\mathrm{2}}$O$_{\mathrm{3}}$ and GaPO$_{\mathrm{4}}$ formation. A ``phase diagram'' of GaP(111) oxidation under various O$_{\mathrm{2}}$ pressures and temperatures can help us visualize transition states and gain more insights into chemical pathways leading to the final products of GaP oxidation. Further, an estimation of work function changes of the oxidized GaP surface was obtained under near ambient conditions. [Preview Abstract] |
Thursday, March 5, 2015 10:24AM - 10:36AM |
S26.00007: One Dimensional Surface Phonon Polaritons in Boron Nitride Nanotubes: High Field Confinement and Localization Xiaoji Xu, Behnood Ghamsari, Dmitri Golberg, Pierre Berini, Gilbert Walker We report the direct observation of one dimensional surface phonon polaritons (SPhPs) in boron nitride (BN) nanotubes at the mid infrared frequencies. High spatial resolution infrared near-field microscopy is used to spatially map the distribution of SPhPs in BN nanotubes. The polaritonic wavelength is experimentally found to be tuneable by the tubular diameter as well as the configurations of the conductive supporting substrate. Effective refractive index of the SPhPs is found to be as high as $\sim$ 70 for a thin BN nanotube. Furthermore, strong field localization and mitigation of the polariton damping is achieved with the use of a rough gold substrate. The randomly spaced nanometer-sized gold grains on the substrate act as distributed reflectors for propagating SPhPs, and confined the surface waves in the one-dimension nanotube. Such geometry allows high field concentration at mid infrared frequencies for chemical sensing and nonlinear optics. Given the analogy between phonon polaritons and plasmon polaritons, BN nanotubes can be used for building blocks for nano-photonics devices in the mid infrared frequencies, with design principles learnt from well-established metallic plasmonics. [Preview Abstract] |
Thursday, March 5, 2015 10:36AM - 10:48AM |
S26.00008: Characterization of Size, Anisotropy, and Density Heterogeneity of Nanoparticles by Sedimentation Velocity Borries Demeler A critical problem in materials science is the accurate characterization of the size dependent properties of colloidal inorganic nanocrystals. Due to the intrinsic polydispersity present during synthesis, dispersions of such materials exhibit simultaneous heterogeneity in density, molar mass, and particle diameter. The density increments with respect to diameter and molar mass of these nanoparticles, if known, can then provide important information about crystal growth and particle size distributions. For most classes of nanocrystals, a mixture of surfactants is added during synthesis to control their shape, size, and optical properties. However, it remains a challenge to accurately determine the amount of passivating ligand bound to the particle surface post synthesis. The presence of the ligand shell hampers an accurate determination of the nanocrystal diameter. Using CdSe and PbS nanocrystals, and the silver nanoparticle (M4Ag44(p-MBA)30), as model systems, we describe how appropriate parametrizations of the flow equation can be used to extract high resolution composition information for mixtures of solutes that are heterogeneous in two out of three hydrodynamic parameters when the third is known. We show how this approach can yield important detail to the understanding of solution composition. [Preview Abstract] |
Thursday, March 5, 2015 10:48AM - 11:00AM |
S26.00009: Design of photo-absorption properties of hybrid organic-inorganic halide perovskite photovoltaic devices by cation manipulation Oscar Granas, Dmitry Vinichenko, Efthimios Kaxiras Photovoltaic devices based on hybrid organic-inorganic halide perovskite materials have lately sailed up as one of the most promising technologies for cost effective harvest of solar energy. In just a few years the efficiency has surpassed that of both conventional dye-sensitized- and organic solar cells. In this study we investigate the influence of the size of the cationic $\pi $-system on the electronic and structural properties of the perovskite photo-absorbing material. Using theoretical simulations we investigate key quantities for photovoltaic efficiency, such as band-gap, electron- and hole mass. We show that by changing the cation the band-gap and effective masses can be controlled. Structural changes are addressed, where we can see an enhanced influence of dispersion interaction as the cation polarizability increases. The effects of spin-orbit coupling is considered for both structural and electronic properties. [Preview Abstract] |
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