Bulletin of the American Physical Society
Joint Fall 2009 Meeting of the Texas Sections of the APS, AAPT, and SPS
Volume 54, Number 13
Thursday–Saturday, October 22–24, 2009; San Marcos, Texas
Session C2: Nanoscience |
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Chair: Jennifer Steele, Trinity University Room: LBJ Student Center 3-13.1 |
Friday, October 23, 2009 2:00PM - 2:12PM |
C2.00001: A Universal Mechanism for Ultrafast Laser Pulse Control of Vibrational Excitations Xiang Zhou, Zhibin Lin, Chenwei Jiang, Roland Allen An important task for ultrafast laser techniques is to control the vibrational excitations of materials. Recently off-resonant ultrafast laser experiments show that the vibrational excitation modes and amplitudes depend on the properties of the laser pulses. A numerical-simulation investigation has suggested that the vibrational excitations depend only on the laser pulse duration, but did not provide a clear and satisfactory explanation. Our theoretical investigation for carbon nanotubes shows that there exists a universal mechanism for controlling vibrational excitations by ultrafast laser pulses, which is independently confirmed by our numerical simulations with semiclassical electron-radiation-ion dynamics (SERID). [Preview Abstract] |
Friday, October 23, 2009 2:12PM - 2:24PM |
C2.00002: Coupled dynamics of electron quasiparticles, the electromagnetic field, and nuclear motion in complex systems Roland Allen, Xiang Zhou, Meng Gao, Chenwei Jiang, Zhibin Lin A vast number of problems in physics, chemistry, biology, and engineering involve the coupled dynamics of electrons and ions in materials and molecules, and their interaction with the radiation field. Here we review some recent work by the present investigators in both developing new techniques to address these problems and performing detailed simulations for systems that are currently of intense interest -- for example, graphene and carbon nanotubes. The new theoretical ideas focus largely on (1) the inclusion of many-body effects (through e.g. a time-dependent GW self-energy) and (2) the use of the Kadanoff-Baym equations for nonequilibrium Green's functions. We will derive a time-dependent quasiparticle equation, which is the time-domain and nonequilibrium version of the well-known frequency-domain and equilibrium quasiparticle equation derived by Hedin and subsequently used by many groups (to obtain e.g. the correct band gaps of semiconductors). [Preview Abstract] |
Friday, October 23, 2009 2:24PM - 2:36PM |
C2.00003: Dynamical simulations of photochemical reactions of \textit{trans}-stilbene, and coherent control of C$_{60}$ vibrational response Chenwei Jiang, Fuli Li, Ruihua Xie, Roland Allen \textit{Trans}-to-\textit{cis} photoisomerization of stilbene, induced by a femtosecond-scale laser pulse, has been observed in simulations employing semiclassical electron-radiation-ion dynamics (SERID). Our results demonstrate that \textit{trans}-to-\textit{cis} and \textit{cis}-to-\textit{trans} isomerization involve the same basic mechanism. We also predict that another photochemical reaction, photocyclization of \textit{trans}-stilbene to 4a,4b-dihydrophenanthrene (DHP), can be achieved using an ultrashort laser pulse. Specifically, the trans-stilbene molecule is observed first to isomerize to cis-stilbene (as an excited-state intermediate) after more than one picosecond, and then to form a new bond to become DHP, after a few hundred additional femtoseconds. For C$_{60}$ at low temperature, we predict that specific vibrational modes can be excited by optimally choosing the delay between two femtosecond-scale pulses. [Preview Abstract] |
Friday, October 23, 2009 2:36PM - 2:48PM |
C2.00004: Iron nitride nanoparticles synthesized by inert gas condensation Prasanna Shah, Brent Ford, Andrew Dean, Diandra Pelecky Inert gas condensation (IGC) is a highly versatile technique to synthesize monodisperse nanoparticles (NP). Earlier research done in our group on iron oxide nanoparticles and Fe- and Co- based fluids suggests that these NP's are well suited for magnetic drug delivery, however, their utility would be dramatically enhanced if they exhibited higher saturation magnetization. Iron-oxide nanoparticles are the most commonly studied system; however, the saturation magnetization (70-90 emu/g) is considerably lower than pure Fe (210 emu/g). Fe NPs tend to oxidize easily, so we are exploring Fe-N and Fe-C alternatives. We have used IGC to synthesize Fe-N nanoparticles (mean sizes $\sim $ 10-20 nm) using Fe deposition followed by gaseous nitrogenation, and via reactive inert-gas condensation. Post-deposition nitrogenation does not form Fe-N phases, nor protect the nanoparticles from oxidation. By reactive sputtering with varying relative concentration of N:Ar, we can produce Fe$_{x}$N phases ranging from x=1 (non-magnetic $\gamma $-FeN) x=4. A systematic study of nitride phase formation as a function of Ar/N$_{2}$ ratio during sputtering will be reported. [Preview Abstract] |
Friday, October 23, 2009 2:48PM - 3:00PM |
C2.00005: Fe/Au Core-Shell Nanoparticles for Biomedical Applications Amandeep Sra, Diandra Leslie-Pelecky The physical properties of nanoparticles, including size, composition and surface chemistry, greatly influence biological and pharmacological properties and, ultimately, their clinical applications. Superparamagnetic iron oxide nanoparticles are widely used for applications such as MRI contrast agents, drug delivery via magnetic targeting and hyperthermia due to their chemical stability and biocompatibility; however, enhancing the saturation magnetization (M$_{s})$ of nanoparticles would produce greater sensitivity. Our design strategy involves a bottom-up wet chemistry approach to the synthesis of Fe nanoparticles. Specific advantages of Fe are the high value of M$_{s}$ (210 emu/g in bulk) coupled with low toxicity; however, Fe nanoparticles must be protected from oxidation, which causes a dramatic reduction in M$_{s}$. To circumvent oxidation, Fe nanoparticles are coated with a Au shell that prevents the oxidation of the magnetic core and also provides the nanoparticles with plasmonic properties for optical stimulation. Ligands of various functionalities can be introduced through the well established Au-thiol surface chemistry for different biomedical applications while maintaining the magnetic functionality of the Fe core. In this presentation, we will discuss the physical, chemical and magnetic properties of our Fe/Au nanoparticles and their resistance to oxidation. [Preview Abstract] |
Friday, October 23, 2009 3:00PM - 3:12PM |
C2.00006: Multiple-mode grating-coupled enhancement of fluorescence by gold nanowires Iuri Gagnidze, Stephanie Wiele, Jennifer Steele We demonstrate directional enhanced fluorescence emission from a gold wire grating. The dominant enhancement mechanism was shown to be excited fluorophores decaying into surface plasmon modes that radiate via the periodicity of the grating. The emission from fluorophores decaying in this way was strongly directional. The fluorophores efficiently coupled to multiple surface plasmon grating modes on both the top and substrate side of the grating, enhancing a broad spectrum of fluorescence wavelengths. This makes periodic systems more flexible than their nanoparticle counterparts. Coupling to multiple modes also allows gratings to enhance fluorescence at wavelengths smaller than the period of the grating, allowing gratings with micron and larger sized features to enhance fluorescence wavelengths in the visible range. This greatly loosens fabrication requirements for potential applications. [Preview Abstract] |
Friday, October 23, 2009 3:12PM - 3:24PM |
C2.00007: Reduction Kinetics of Graphene Oxide Determined by Temperature Programmed Desorption Carl Ventrice, Nicholas Clark, Daniel Field, Heike Geisler, Inhwa Jung, Dongxing Yang, Richard Piner, Rodney Ruoff Graphene oxide, which is an electrical insulator, shows promise for use in several technological applications such as dielectric layers in nanoscale electronic devices or as the active region of chemical sensors. In principle, graphene oxide films could also be used as a precursor for the formation of large-scale graphene films by either thermal or chemical reduction of the graphene oxide. In order to determine the thermal stability and reduction kinetics of graphene oxide, temperature program desorption (TPD) measurements have been performed on multilayer films of graphene oxide deposited on SiO$_{2}$/Si(100) substrates. The graphene oxide was exfoliated from the graphite oxide source material by slow-stirring in aqueous solution, which produces single-layer platelets with an average lateral size of $\sim $10 $\mu$m. From the TPD measurements, it was determined that the decomposition process begins at $\sim $80 $^{\circ}$C. The primary desorption products of the graphene oxide films for temperatures up to 300 $^{\circ}$C are H$_{2}$O, CO$_{2}$, and CO, with only trace amounts of O$_{2}$ being detected. An activation energy of 1.4 eV/molecule was determined by assuming an Arrhenius dependence for the decomposition process. [Preview Abstract] |
Friday, October 23, 2009 3:24PM - 3:36PM |
C2.00008: In-situ dispersion and optical manipulation of magnetic carbon nanoparticles Sunil Gusain, Samarendra Mohanty, Ali Koymen Magnetic carbon nanoparticles are finding increasing use in enhancing contrast of imaging and photo thermal therapy of cancer. However, conventional synthesis of these nanoparticles involves very cumbersome and skillful interventions. We developed a simple method for controlled synthesis of amorphous carbon nanoparticles using dense medium plasma generated in the cavitation field of an ultrasonic horn in Benzene using two metal electrodes. In this method, the electrode (magnetic) material is incorporated into the C nanoparticles, as confirmed by hysteresis curve, measured using SQUID magnetometer. TEM images showed that the size of the C nanoparticles is in the range of 8-14 nm and the electron diffraction established that these nanoparticles are amorphous. The absorption spectrum in near-IR region was measured to be of similar value as in the visible region, making it a very useful candidate for photothermal therapy using near-infrared laser in the biological window. These carbon nanoparticles aggregates and tend to form clusters. For in-situ dispersion of these nanoparticles, we made use of the absorption property of these nanoparticles using a focused near-IR cw laser microbeam (1064nm). We believe the magnetic property of these nanoparticles would allow effective localization in the tumor region by application of external magnetic field. [Preview Abstract] |
Friday, October 23, 2009 3:36PM - 3:48PM |
C2.00009: The nanoscale grain size of materials of electrodes of AMTEC and its longevity M.A.K. Lodhi, Javid Sami The Alkali Metal Thermal-to-Electric Converter (AMTEC) is perhaps one of the most desirable devices for directly converting heat into electrical energy, particularly for space applications. Two major components responsible for power output of AMTEC are the electrolyte and the electrode. In this work we have focused the research on the AMTEC electrodes, which have further reduced the power degradation as the time goes by in using the AMTEC. If the grain size of the electrode material reaches a certain dimension, about 750 nm, the power output starts degrading fast. It is very important because this condition should not occur until after the desirable lifetime of AMTEC and its acceptable fraction of power degradation have reached. We have worked out the parameters for a 15 years of life and 10{\%} of acceptable power degradation factor for various electrode materials. This study aims at improving the performance of the electrode by looking into the changes of the material properties with respect to time. These parameters refer to the grain growth involved in the grain mobility model for electrode materials [Preview Abstract] |
Friday, October 23, 2009 3:48PM - 4:00PM |
C2.00010: A lanthanide complex doped silica thin film for detecting trace chemical toxins John Como, Louisa Hope-Weeks, Kelvin Cheng A highly luminescent lanthanide metal--ligand complex was doped into a mesoporous silica sol-gel matrix for the development of a nanosensor to detect trace toxic chemicals. The metal ion Eu$^{3+}$ was coordinated with various organic ligands to produce different self-assembling compounds that exhibit different sensitivity to targeted chemical toxins. Under ultra-violet excitation, the compound exhibited intense, long-lived millisecond phosphorescence with a large Stokes shift. A detector was fabricated by doping a silica sol-gel thin film matrix with the Eu$^{3+}$ compound and was exposed to liquid and gas phase toxins. Upon exposure, the compound underwent fast fluorescence quenching and the emission/source intensity ratio was measured as a function of time for various concentrations of toxins. [Preview Abstract] |
Friday, October 23, 2009 4:00PM - 4:12PM |
C2.00011: The formation of silicon nanoparticles at atmospheric pressure by rapid thermal anneal Justin Frasier, Jonathan Preiss, Benedict Anyamesem-Mensah, Anup Bandyopadhyay, Gregory Spencer In this study, the formation of silicon nanoparticles by thermal annealing of an initial silicon-on-insulator (SOI) structure is being performed. The SOI samples are synthesized by thermal oxidation of Si (100) wafers followed by magnetron or ion beam sputtering of a thin Si top layer. The thermal anneals are performed in a rapid thermal anneal system at temperatures ranging from 600$^{\circ}$C to 900$^{\circ}$C under atmospheric pressure of flowing Ar gas. The nanoparticle formation process is being studied as a function of the thermal anneal temperature, anneal time, and Si layer thickness. The annealed samples are measured by atomic force microscopy to determine the resulting nanoparticle size distributions and synthesis details. Electron microscopy is also being used for analysis. Results for these synthesis experiments and comparisons with other methods will be presented. [Preview Abstract] |
Friday, October 23, 2009 4:12PM - 4:24PM |
C2.00012: Synthesis and Characterization of Double Metal Hydroxide Nanoparticles Gary Beall, Sergio Crosby, Yelena Vecherkina A series of double metal hydroxide nanoparticles have been synthesized under hydrothermal conditions with varying charge density. The effect on dispersibility and catalytic behavior have been studied for these particles as a function of charge density. Several of the samples have been converted to organophobic forms by ion exchanging the chloride with various carboxylic acids. The stability studies of dispersion of these organophillic nanoparticle in a number of organic solvents has also been conducted. All of the samples have been characterized by TGA. SEM, XRD, and DSC and data from all of these techniques will be reported. The catalytic decomposition of these materials will also be report. [Preview Abstract] |
Friday, October 23, 2009 4:24PM - 4:36PM |
C2.00013: Aberrated Optical Tweezers For Manipulation Of Nanoparticles Samarendra Mohanty, Kunal Tiwari Asymmetry leading to aberrations is the most unwanted parameter in optics, especially while working on a microscopic system such as optical tweezers using high numerical aperture microscope objectives. While considerable efforts are being made to minimize aberrations in optical tweezers for stable trapping, optical tweezers that are asymmetric in size along transverse directions due to astigmatic beams, enabled controlled rotation of microscopic objects. More interestingly, adding further aberrations (such as coma) in the intensity profile of the asymmetrically shaped optical tweezers, even more complex tasks such as parallel transport of microscopic objects has been achieved. Here, we report transport of dielectric nanoparticles of different sizes using aberrated optical tweezers. The aberrated optical tweezers was generated by using Gaussian output from Ytterbium fiber laser which was first stretched using a cylindrical lens and subsequent aberrations were introduced by either tilting the beam with respect to the microscope objective or by use of an additional lens. We could generate the asymmetric potentials selectively in a controlled way in X and or Y-directions over an extended spatial region. This development would further facilitate the growing use of optical tweezers for mixing as well as sorting at nano level. [Preview Abstract] |
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