Bulletin of the American Physical Society
74th Annual Meeting of the Southeastern Section
Volume 52, Number 13
Thursday–Saturday, November 8–10, 2007; Nashville, Tennessee
Session JB: Molecules, Nanostructures and Surfaces |
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Chair: Laura Clarke, North Carolina State University Room: Scarritt-Bennett Center Laskey C |
Friday, November 9, 2007 1:30PM - 1:42PM |
JB.00001: Molecular Motion in Poly(vinylmethylsiloxane) Derrick Stevens, Julie Crowe-Willoughby, Jan Genzer, Laura Clarke Responsive surfaces~change their physico-chemical characteristics upon the introduction of external stimuli. Modified poly(vinylmethylsiloxane) (PVMS) networks have been shown to exhibit rapid wettability changes due to surface reconstruction~ upon exposure to water [Crowe, J.A.; Genzer, J., J. Am. Chem. Soc. 127, 17610-17611 (2005)].~We aim~to correlate the dynamics of the side and backbone motion within the modified PVMS networks to the observed surface chemistry rearrangement. Polymer samples were placed upon interdigitated electrodes and dielectric relaxation spectroscopy, as a function of temperature, was conducted. This technique allows us to probe the network and see changes in molecular motion as a function of temperature and network composition.~ Dynamic mechanical analysis (DMA) was also performed and coincided well with the dielectric results. The side chain motion and their effect on the response of the PVMS network will be discussed. [Preview Abstract] |
Friday, November 9, 2007 1:42PM - 1:54PM |
JB.00002: Spatially resolved micro-Raman spectroscopy on nanostructured surfaces Jed I. Ziegler, Dimitri S. Koktysh, Kevin A. Tetz, Richard F. Haglund, Jr. Surface-enhanced Raman scattering (SERS) is a promising technique for detecting weak molecular fingerprints for ultrasensitive chemical analysis. SERS arises from plasmonic electric field effects on surfaces with nanoscale asperities. We are using nanoparticles (NPs) and NP arrays tailored specifically for SERS in order to enhance sensitivity and correlate experimental result with finite-difference time- domain calculations of the nanoscale electromagnetic fields. Gold NPs and silver-gold core-shell NPs are prepared either by self-assembly into NP colloids or by lithographic fabrication into NP arrays on silicon substrates. Benzenethiol and other molecules with thiol groups are then spread on the NP-covered substrate where they bind to the gold surfaces of the NPs. Spatially resolved Raman spectra from NP colloids or single NPs with approximately 250 nm lateral resolution are obtained in a confocal inverted microscope configuration, while visible reflectivity measurements are used to correlate the location of the analyte molecules with particle morphology. [Preview Abstract] |
Friday, November 9, 2007 1:54PM - 2:06PM |
JB.00003: Measurements of Long-Lived Radicals in Ultra-High Molecular Weight Polyethylene Muhammad Jahan, Muhammad Fuzail, Marlon Ridley, Benjamin Walters Ultra-high molecular weight polyethylene (UHMWPE), a polymer of choice for orthopedic applications, was gamma-irradiated in air, nitrogen or vacuum at 22\r{ }C and subsequently aged for 10 years in its own environment at 22\r{ }C, 37\r{ }C, or 75\r{ }C. Free radical measurements were conducted using an X-band electron spin resonance (ESR) spectrometer. The samples aged in sealed environments (nitrogen or vacuum) show the presence of the primary radicals (alkyl, allyl, polyenyl), although the concentration of these radicals in each case is very low to insignificant. However, there is no detectable transformation from the primary to oxygen-induced radicals (OIR). The ESR spectra of the open samples, on the other hand, show the presence of only OIR. Similar OIRs are detected in retrieved hip- and knee-joint parts 18 years after retrieval. These joints were gamma-irradiated in air prior to implantation, and were retrieved 6-8 years after use. OIRs are also detected in vitamin-E-doped UHMWPE after gamma irradiation in nitrogen and subsequent exposure to air for one year. [Preview Abstract] |
Friday, November 9, 2007 2:06PM - 2:18PM |
JB.00004: Second harmonic generation in arrays of centrosymmetric gold nano-dimers Davon W. Ferrara, Kevin A. Tetz, Matthew D. McMahon, Richard F. Haglund, Jr. Second-harmonic generation (SHG) is an important signature of electron dynamics in nanoparticles as well as a sensitive probe of surface effects. In the gap between closely spaced pairs of nanoparticles, or nanodimers (ND), localized electromagnetic field energy creates a ``hot spot'' that has been shown to affect SHG from asymmetric NDs. We will present new experimental results demonstrating the role that gap size and field localization plays in SHG from centrosymmetric ND arrays. Arrays of ellipsoidal nanoparticles were fabricated using focused ion-beam lithography techniques with gold deposited via thermal evaporation to give particles 20 nm in height with varying areal aspect ratios. In the ND arrays, symmetry forbids SHG in the forward direction, but not at larger angles. Our experiments indicate suppression in SHG intensity with decreasing gap size and evidence of stronger long range interactions between particles with separation over 200 nm. Finite-difference time-domain (FDTD) simulations were also performed in order to correlate field localization with SHG. Our simulations show a strong dependence on the polarization of incident light. [Preview Abstract] |
Friday, November 9, 2007 2:18PM - 2:30PM |
JB.00005: Novel Optoelectronic Transport Studies of Supramolecular Nanotube Assemblies Harsh Chaturvedi, Jordan Poler Single Walled Carbon Nanotubes (SWNT) are important materials for future devices and sensors.. Ruthenium complexes have very strong absorbance in the visible spectrum. SWNTs have exceptional electron accepting and charge transfer properties. We have shown specific binding of these complexes with the end of SWNTs. Properties of these supramolecular nano-assemblies are being investigated to develop applications like sensors and photovoltaic cells. Photon enhanced aggregation properties of SWNT due to these ruthenium complexes are demonstrated. These organometalic based molecular adsorbates onto the nanotubes affect the field effect transistor response of SWNTs.~ Ruthenium centered phenanthroline complexes exhibit a strong metal to ligand charge transfer. We believe that the nanotube quenches charge from the ligand after the complex has been optically excited. This results in optically altering the carrier density, and therefore the transport properties of the nanotubes.~ We believe this is due to charge transfer from the metal center through the ligand and finally onto the nanotubes. Photon induced affects on the charge transport are shown. Advancements towards realizing real-time optoelectronic sensors and nano devices are demonstrated. [Preview Abstract] |
Friday, November 9, 2007 2:30PM - 2:42PM |
JB.00006: Optical Properties of Helical Ag Nanostructures calculated by Discrete Dipole Approximation Method Zhongyue Zhang, Yiping Zhao As a commonplace structure in nature, helical structure remains a mystery to scientific researchers, which interacts differently with left and right circularly polarized light, and gives the well-known phenomena of circular birefringence and circular dichroism. Most helical structures studied so far are dielectric or molecular structures. In this presentation, the extinction spectra and field distribution of Ag helical nanostructures calculated using the discrete dipole approximation method have been investigated. The plasmon peak of the Ag helix can be tuned not only by the structural parameters but also by the polarizations of the incident light, especially the circular polarizations. In addition, the polarization direction of the incident light can change the spatial distribution of the maximum $E$ field, which provides a simple way to spatially resolve analyte's distribution on the nanostructures for sensing applications. [Preview Abstract] |
Friday, November 9, 2007 2:42PM - 2:54PM |
JB.00007: AC Field Modulation of Diffraction in Dye and Carbon Nanotube Doped Liquid Crystal Permanent Gratings Gene Carlisle, Mikail Abbasov, Tina Maxwell We have written permanent gratings in planar nematic liquid crystal (LC) cells doped with Methyl Red (MR) and single-wall carbon nanotubes (CNT). This was accomplished using low-intensity visible light and without application of electric fields. The diffraction efficiency can be enhanced and controlled with ac fields. We report our results for voltages ranging as high as 21 V and frequencies ranging from near zero to 1 MHz. Cells doped with both MR and CNT produced approximately twice the diffraction efficiency as cells doped only with MR. A mechanism is proposed for grating formation based on trans-cis photoisomerism of MR followed by adsorption of the cis-isomer on the alignment layers in the bright regions of the light interference pattern. The gratings are robust and have remained stable for over two years. [Preview Abstract] |
Friday, November 9, 2007 2:54PM - 3:06PM |
JB.00008: Surface Electromagnetic Phenomena in Pristine and Doped Carbon Nanotubes Igor Bondarev Recent theoretical effort towards understanding the near-field optoelectronic properties of pristine and atomically doped carbon nanotubes will be reviewed. The research is motivated by the need for the development of materials that may host quantum coherent states with long coherence lifetimes [1]. A variety of electromagnetic phenomena, such as atomic spontaneous decay dynamics [2] and atom-nanotube van der Waals coupling[3], light absorption [4,6] and entanglement of atomic states [5,6] close to carbon nanotubes, exciton-plasmon interactions on the nanotube surface [7], as well as their potential applications in modern nanophotonics and optoelectronics, will be discussed. [1] T.Brandes, Phys. Rep. 408, 315 (2005). [2] I.V.Bondarev, Ph.Lambin, Phys. Rev. B 70, 035407 (2004). [3] I.V.Bondarev, Ph.Lambin, Phys. Rev. B 72, 035451 (2005). [4] I.V.Bondarev, B.Vlahovic, Phys. Rev. B 74, 073401 (2006). [5] I.V.Bondarev, B.Vlahovic, Phys. Rev. B 75, 033402 (2007). [6] I.V.Bondarev, Journal of Electronic Materials, \textit{in print}. [7] I.V.Bondarev, H.Qasmi, Physica E, \textit{in print}. [Preview Abstract] |
Friday, November 9, 2007 3:06PM - 3:18PM |
JB.00009: ZnO Nanowires for PV: Size Control and Scalability Studies Darlene Gunther, Jenifer Lawrie, Akira Ueda, Richard Mu Our research attempts to understand the carbothermal vapor- solid growth process for novel ZnO nanowires (NW's). In addition to being a relatively simple growth process, the ZnO NW's, most often n- type, have high electron mobility and a large bandgap (3.4 eV). This makes them an attractive electron conductor. Our team expects these ZnO NW's to provide a means of reducing the charge recombination problems currently hampering the efficiencies of photovoltaic (PV) cells. Current growth methods are limited to small sample sizes in a horizontal tube furnace. We propose an innovative vertical design that provides optimal control of the growth parameters, allowing us to study each of the factors to determine their role in growing the required ZnO structures, e.g. gas flow turbulence, oxygen supply, distance from source to substrate, temperature control and uniform density. We report the results of our initial experiments where we grew dense ZnO nw's on a large (11.3 x 44.8 mm) silicon substrate (100). [Preview Abstract] |
Friday, November 9, 2007 3:18PM - 3:30PM |
JB.00010: Photosensitization of ZnO nanowires via pulsed electron beam deposition of CdTe quantum dots. Roberto Aga, Dawit Jowhar, Akira Ueda, Zhengda Pan, Richard Mu We demonstrate the photosensitization effect of CdTe quantum dots (QDs) on ZnO nanowires (ZnO-NWs). The QDs are directly deposited on a network of ZnO-NWs grown on glass substrate via pulsed electron beam deposition technique under 17 millitorr argon background gas pressure. The ablation parameters that we employ result to an average deposition rate of 0.06 nm/pulse. CdTe deposition with 25 pulses increases the photocurrent at 2V-bias of the ZnO-NWs by an order of magnitude under sub-bandgap illumination. Before photosensitization, the ZnO-NWs already exhibit weak sub-bandgap photoconductivity due to the presence of defect states between the bandgap. The enhancement in photoconductivity that resulted from the deposition of QDs, which can absorb photons with wavelengths up to 800 nm, is attributed to the efficient transfer of photo-excited electrons from the conduction band of CdTe towards the conduction band of ZnO. [Preview Abstract] |
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