Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session B10: Focus Sessions: Physical Chemistry of Nanoscale System II |
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Sponsoring Units: DCP Chair: Haw Yang, University of California, Berkeley; Clemens Burda, Case Western Reserve University Room: Baltimore Convention Center 302 |
Monday, March 13, 2006 11:15AM - 11:51AM |
B10.00001: Potential Application of the Enhanced Absorption and the Enhanced Scattering Processes of Plasmonic (Gold and Silver) Nanoparticles of Different Shapes Invited Speaker: The crossections of absorption and scattering of plasmonic nanoparticles are orders of magnitude larger than those of molecular dyes. Their strong scattering properties make them much better contrast agents in biological and medical applications than fluorescent dyes. Their strong absorption makes them useful in photothermal therapy and in changing their shape or their location in assembled arrays. These applications will be illustrated. [Preview Abstract] |
Monday, March 13, 2006 11:51AM - 12:03PM |
B10.00002: Studying Photoluminescence Dynamics of Single Quantum Dots Photon by Photon Haw Yang, Kai Zhang, Aihua Fu, Paul Alivisatos, Carl Hayden Colloidal semiconductor nanocrystals, or quantum dots (QDs), have been the focus of much research effort in the past decade. The development of these colloidal dots has allowed the concepts of quantum confinement and dimensional control of electronic and optical properties to find entirely new areas of application, for instance in fluorescent labeling of biological specimens. At the single-particle level, however, colloidal QDs exhibit surprisingly complicated time-dependent behavior in their photoluminescence (PL) characteristics. The PL dynamics of the biologically compatible CdSe/ZnS/streptavidin quantum dots were studied using time-resolved single-molecule spectroscopy. Statistical tests of the photon-counting data suggested that the simple ``on/off'' discrete state model is inconsistent with experimental results. Instead, a continuous emission state distribution model was found to be more appropriate. Autocorrelation analysis of lifetime and intensity fluctuations showed a nonlinear correlation between them. These results were consistent with the model that charged quantum dots were also emissive, and that time-dependent charge migration gave rise to the observed photo-luminescence dynamics. [Preview Abstract] |
Monday, March 13, 2006 12:03PM - 12:15PM |
B10.00003: Photothermal properties of gold nanocages studied by time-resolved spectroscopy Min Hu, Jingyi Chen, Younan Xia, Xingde Li, Hristina Petrova, Gregory Hartland, Manuel Marquez Gold nanocages of different sizes synthesized via galvanic replacement reaction have been studied by ultrafast time-resolved spectroscopy. The vibrational phonon modes were excited and the periods of these modes increase with the size of the gold nanocages. For a specific size of nanocage, experiments with different excitation powers of the pump laser were performed (from 2 $\mu $J to 20 $\mu $J), we found that the period of the vibrational mode increased with the laser intensity. This was compared to experiments on spherical gold nanoparticles, which allow us to roughly estimate the temperature of the nanocages when the electrons and the phonons reach the equilibrium. The temperature of the nanocages can increase up to 1000 K, near the melting point of the bulk metal, while the particles maintain their integrity. This makes the nanocages potentially useful for photothermal therapy applications. The heat dissipation rate for the nanocages was also studied in these experiments, and was found to have the similar trend as spherical nanoparticles, i.e., larger particles stay hot for longer times than smaller particles. [Preview Abstract] |
Monday, March 13, 2006 12:15PM - 12:27PM |
B10.00004: Photoluminescence and Dynamics Measurements of Individual CdSe Quantum Wires John Glennon, Rui Tang, William Buhro, Richard Loomis The photoluminescence (PL) spectroscopy of highly monodispersed colloidal CdSe quantum wires (QWs) are investigated in the single nanocrystal environment using confocal fluorescence microscopy and are compared to similar studies preformed on three dimensionally confined CdSe quantum dots (QDs). The PL intensity of the QWs is observed to increase and then to decrease at room temperature ambient conditions with continued irradiation at moderate to high laser powers ($>$10 kW*cm$^{-2})$ at much slower rates than similar processes in QDs. The energy of the peak intensity of the PL is monitored throughout the experiments and does not shift for the QWs. This is in contrast to the blue-shift observed for QDs as the PL intensity decays. For the QWs, it is shown that the change in PL intensity is localized to the diffraction limit irradiation spot and is not delocalized along the length of the QW. Differences in exposed crystalline facets and surface coverage between QWs and QDs are explored in context of the experimental observations. These phenomena are studied under different atmospheres and surface environments in order to elucidate the optical properties of these quantum-confined semiconductors. [Preview Abstract] |
Monday, March 13, 2006 12:27PM - 12:39PM |
B10.00005: Photo-Induced Single Molecule Electron Transfer at the Molecule-Nanoparticle Interface Tianquan Lian, Wanhee Goh, Jianchang Guo, Xi Liu, Michael Ahrens, Emilie Schierloh, Michael Wasielewski Single molecule fluorescence spectroscopy was used to study photoinduced electron transfer (ET) dynamics across single donor-bridge-acceptor junctions consisting of perylene-3,4:9,10-bis(dicarboximide) (PDI), n-phenylene bridge with COOH anchoring group, and antimony doped Tin Oxide(ATO) nanoparticles. Photo-excitation of PDI initiates electron transfer from its excited state into ATO nanoparticles. Electron transfer was confirmed and ensemble average rate was measured by transient infrared absorption spectroscopy, in which injected electrons in ATO were directly monitored. Single molecule fluorescence from donor molecule was confirmed by the observed blinking behavior, fluorescence spectrum, and excitation polarization dependence. Single molecule fluorescence lifetime was measured by time-correlated single photon counting, from which forward electron transfer rate from adsorbate excited state to nanoparticle was determined. The dependence of these single molecule ET rates and their fluctuation on the length of phenylene bridge and the nature of semiconductors are being investigated. [Preview Abstract] |
Monday, March 13, 2006 12:39PM - 1:15PM |
B10.00006: Dynamics of photoexcitations in quasi-one-dimensional systems Invited Speaker: Low dimensional materials, and in particular, quasi-one-dimensional systems have attracted considerable interest owing to their unusual electronic properties. In many of these systems, strong electron-phonon couplings can lead to the formation of nonlinear excitations such as self-trapped excitons and polarons, in which electronic excitations become localized as a result of their interaction with the lattice. I will present the results of femtosecond time-resolved experiments in which we have studied the dynamics of the formation and evolution of localized excitations in quasi-one-dimensional molecular solids. This work has been carried out on mixed-valence halide-bridged transition metal linear chain (or MX) complexes, a class of materials that serve as model systems for the physics of low-dimensional materials. In these complexes, the relative strengths of the electron-electron and electron-phonon interactions, the fundamental physical parameters that determine the properties of the excitations, can be systematically tuned by chemical substitutions in the chain structure. Using femtosecond vibrationally impulsive excitation techniques, we have studied the coupled electronic and vibrational dynamics associated with excitonic self-trapping in a series of quasi-one-dimensional structures, and using time-resolved THz techniques, we have studied the dynamics of the formation and subsequent evolution of polarons. [Preview Abstract] |
Monday, March 13, 2006 1:15PM - 1:27PM |
B10.00007: Dynamics of the heat transfer at the interface of diamond {\{}111{\}} nanosurfaces. Oleg A. Mazyar Energy transfer across the interface between a small, hot model diamond {\{}111{\}} nanosurface and a much larger identical, cold nanosurface was studied by a classical molecular dynamics method. Kinetics of this energy transfer was found to be exponential with a rate constant increasing linearly with the increase of the normal load applied to the hot nanosurface. The rate constant of the heat transfer depends on the thickness of the small, hot nanosurface, both chemical and isotopic composition of the interface, but does not demonstrate significant changes with the increase of the nanosurfaces' contact area or the increase of the initial temperature difference between the nanosurfaces. [Preview Abstract] |
Monday, March 13, 2006 1:27PM - 1:39PM |
B10.00008: The Static and Dynamic Wetting of Si Nanorod Arrays Jianguo Fan, Yiping Zhao The wettability of a solid state surface is affected by both the surface roughness and the surface chemical composition. Here, we report a systematic investigation on the static and dynamic wetting of vertically aligned Si nanorod arrays with different heights (aspect ratio) fabricated by the glancing angle deposition technique. For as-deposited hydrophilic films, there was a contact angle transition from a rough surface to a hemi-wicking porous surface at normal film thickness $d$ = 500 nm; while for the HF treated hydrophobic films, a transition from partial composite to composite surface was observed at the same film thickness. The observed results can be reasonably interpreted within framework of the classic Young's theory. We have also observed that for the hydrophilic nanorod arrays, the spreading of the water droplet causes the bundling of Si nanorods, and generates intriguing percolation patterns that change with the spreading diameter. The dynamic spreading process of a water droplet on the same surface has been recorded by a fast CCD camera, and scaling laws of the contact line, the precursor rim, and the spreading speed have been observed. Models based on capillary force, mechanical bending, as well as flow in a groove, have been proposed to qualitatively explain all the phenomena observed. [Preview Abstract] |
Monday, March 13, 2006 1:39PM - 1:51PM |
B10.00009: Inorganic Nanotubes, Nanofluidic Transistors and DNA Translocation Peidong Yang Inorganic nanotubes, representing a new class of nanostructures, have been attracting considerable attention during the past few years. Single crystalline semiconductor GaN nanotubes can be synthesized by nanowire templated epitaxial casting method. Partial conversion of existing nanowires leads to the synthesis of silica nanotubes after etching off remaining cores. Silica nanotubes can be integrated into metal-oxide-solution field effect transistors (MOS\textit{ol}FETs) which exhibit rapid field effect modulation of ionic conductance. Surface functionalization can change inherent carrier concentration as well channel polarity to fabricate p-type, n-type and ambipolar transistors. These nanofluidic devices were further demonstrated to be useful in single molecule sensing. Single DNA molecules can be electrically detected either by charge effect or geometry effect. These nanofluidic FETs have potential implications in sub-femtoliter analytical technology and large-scale nanofluidic integration. [Preview Abstract] |
Monday, March 13, 2006 1:51PM - 2:03PM |
B10.00010: Monitoring Gold Nanorod Synthesis based on their Localized Surface Plasmon Resonance Amneet Gulati, Hongwei Liao, Jason Hafner The extinction spectra of structurally anisotropic gold nanoparticles exhibit surface plasmon resonances that may be tuned through the visible and near-infrared portions of the electromagnetic spectrum by controlling their geometry. Gold nanorods, whose longitudinal extinction peak is proportional to their aspect ratio, are synthesized by reduction of gold chloride onto gold seed nanoparticles. While growth anisotropy is known to be induced by a surfactant (cetyltrimethylammonium bromide), the detailed growth mechanism is poorly understood. Here, we study the growth kinetics of nanorods by continually monitoring their extinction spectra during synthesis. The spectra are analyzed by Rayleigh-Gans theory to determine the instantaneous length and diameter of the growing nanorods. This data yields microscopic growth rates which provide insight into the mechanism of nanorod synthesis. [Preview Abstract] |
Monday, March 13, 2006 2:03PM - 2:15PM |
B10.00011: Desorption and Dissociation of Water Induced by Photoexcitation of Silver Nanoparticles Dinko Chakarov, Hans Fredriksson The photodesorption and photodissociation of water from silver nanoparticles grown in situ on graphite has been studied by HREELS, TPD and PID. We discuss the factors which influence dissociative versus associative desorption pathways when the system is irradiated with cw and ns pulsed UV light. The observations are attributed to increased optical absorption and hot electron production at the Ag clusters and their vicinity due to particle plasmon excitations. [Preview Abstract] |
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