Bulletin of the American Physical Society
75th Annual Meeting of the Southeastern Section of APS
Volume 53, Number 13
Thursday–Saturday, October 30–November 1 2008; Raleigh, North Carolina
Session BB: Nano-Materials |
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Chair: Ravindra Kumar, Shaw University Room: Holiday Inn Brownstone Washington |
Thursday, October 30, 2008 8:30AM - 8:42AM |
BB.00001: Nonlinear optical properties of semiconductor nanocrystals: theory and experiments Qiguang Yang, Jaetae Seo, Seongmin Ma, William Yu, SungSoo Jung, Bagher Tabibi, Jessica Freeman, Doyle Temple The third-order nonlinearities of various semiconductor nanocrystals have been investigated both theoretically and experimentally. The theoretical calculations have been done by using density matrix method and the experimental measurements have been fulfilled using time-resolved four-wave mixing, Z-scan, and I-scan methods under different experimental conditions. The experimental data have been compared to the theoretical calculations and the physical origins of the third-order nonlinearities of the semiconductor nanocrystals have been discussed. The possible nonlinear photonic device applications of these materials have been suggested. [Preview Abstract] |
Thursday, October 30, 2008 8:42AM - 8:54AM |
BB.00002: Ultrafast intensity-dependent dephasing in CdSe nanocrystals Jessica Freeman, Qiguang Yang, Jaetae Seo, William Yu, SungSoo Jung, Bagher Tabibi, Doyle Temple The intensity-dependent photon-echo relaxation time in CdSe nanocrystals at room temperature was investigated using femtosecond-resolved forward degenerate four-wave mixing (DFWM) at 775 nm. Our studies show that as the intensity of the excitation pulse increased the dephasing time of CdSe decreased.~ The dependency of the dephasing time on the pump intensity is due to instantaneous spectral diffusion which may be caused by collision of the light generated excitons with other excitons, phonons, and/or surface defects. The third-order nonlinear susceptibility of the sample was also measured and will be discussed. [Preview Abstract] |
Thursday, October 30, 2008 8:54AM - 9:06AM |
BB.00003: Synthesis and characterization of nanocrystalline RE-substituted (RE=La, Ce, Gd, Dy, Er, Yb) Mn-Zn ferrites Tatiana Brusentsova, Robert Peale, Nikolay Khokchlatchev, Viatcheslav Kuznetsov Nanocrystalline ferrites Mn$_{0.6}$Zn$_{0.4}$Fe$_{2y}$RE$_{y}$O$_{4}$ (RE=La, Ce, Gd, Dy, Er, Yb; y=0; 0.1; 0.2; 0.3) were synthesized by chemical co-precipitation method. The formation of FCC spinel structure and absence of impurity phases within each of the sample was confirmed by X-ray diffraction analysis. The cationic distribution within ferrites was obtained by atomic emission spectroscopy. Mean particle size calculated by Scherrer's formula from XRD data of dried powders ($\sim $10 nm) is in good agreement with one showed by transmission electron microscopy of the initially obtained particles in a diluted aqueous solution. Scanning electron microscopy confirmed the nanocrystalline morphology of the dried ferrite powders. Magnetic measurements in a temperature range 4 -- 393 K showed a typical superparamagnetic behavior, like non-hysteretic M(H) curves and a blocking temperature on M(T) dependencies. Infrared transmission spectra have been investigated in a range 40-3500 cm$^{-1}$. All spectra show a typical for cubic spinel lattice double peak in far IR, corresponding to the stretch-type vibrations on Me-O bonds in octahedral and tetrahedral sublattices. [Preview Abstract] |
Thursday, October 30, 2008 9:06AM - 9:18AM |
BB.00004: ABSTRACT WITHDRAWN |
Thursday, October 30, 2008 9:18AM - 9:30AM |
BB.00005: Impact of complex geometries on the percolation in nanocomposites D.R. Stevens, L.N. Downen, L.I. Clarke As utilization of nanocomposites (polymer matrix doped with a nanoparticle) expands, the prevalence of composites with complex morphologies is increasing. Nanocomposite materials are desirable in that the addition of a nanoparticle can produce a significant alteration in properties such as electrical conductivity, while retaining some of the processability associated with the neat polymer. Enhancements of the mechanical or electrical properties are dependent on the formation of continuous networks of particle within the composite volume. This percolation process may be significantly influenced by the specific geometry of the composite. In this work the nanostructure of interest is a mat of electrospun nanofibers with diameters of $\sim $100 nm and high porosity. To understand percolation within these mats, two series of Monte Carlo calculations are performed. The critical volume percent is investigated in continuous samples (purposefully non-complex structures) to determine the effect of sample size and shape; this is representative of the percolation in a single fiber. In addition, computational realizations of experimentally produced electrospun mats are tested for critical volume percentages; the aim being to establish which factors of the nanostructure influence the percolation process and how do these results compare to the continuous system. [Preview Abstract] |
Thursday, October 30, 2008 9:30AM - 9:42AM |
BB.00006: Sizing morphology-controlled gold nanoparticles by linear absorption spectroscopy. Jasmine Austin, Qiguang Yang, Jaetae Seo, Bagher Tabibi, Wanjoong Kim, Jinhwa Heo, Sang Woo Han, Wan Soo Yun, SungSoo Jung, Justin Vazquez, Jessica Freeman, Doyle Temple The most remarkable optical property of gold nanoparticles is surface plasmon resonance (SPR) which dramatically differs from its bulk counterpart. Within the frame of Mie theory, we investigated the relationship between the size and the SPR and its corresponding bandwidth. An empirical fitting function will be given for the sizing curve for morphology-controlled gold nanoparticles in water and possible physical mechanisms for the size-dependent optical properties will be discussed in this paper. [Preview Abstract] |
Thursday, October 30, 2008 9:42AM - 9:54AM |
BB.00007: Microscopic investigation on the static polarizability of nanocluster composed of chains of atoms Zachary Bond, Hye-Young Kim, Milton Cole, Darrell Velegol The dispersion interaction between nanoclusters at very large separation may be calculated by considering each cluster as a point particle characterized by a static polarizability tensor. The static polarizability of a cluster is evaluated by including all many-body interactions self-consistently. In the present study, various numbers of chains of atoms, composed of identical or two different atoms at alternating sites along each chain, are chosen as cluster. The results of the present calculation show the effects of anisotropic shape (aspect ratio), finite size, and substance. The dependence on the separation between nearby chains within a cluster is also explored. The static polarizability depends also on material, diverging when a coupling constant $\nu $ reaches a limiting value $\nu _{max}$, where the coupling constant $\nu $ is defined as the atomic polarizability per unit volume. We will present microscopic (atomic) views on how the static polarizability of a cluster varies over a wide range of $\nu$ values. [Preview Abstract] |
Thursday, October 30, 2008 9:54AM - 10:06AM |
BB.00008: A novel method for size uniform 200nm particles: multimetallic particles and in vitro gene delivery Lamar Mair, Kris Ford, Richard Superfine We report on the fabrication of arrays of mono- and multimetallic particles via metal evaporation onto lithographically patterned posts. Metal particles evaporated on cylindrical structures 0.20$\mu$m in diameter and 0.33$\mu$m tall are released via photoresist dissolution, resulting in freely suspended, shape defined particles. These Post-Particles have highly tunable composition, as demonstrated by our deposition of five different multimetallic particle blends. We calculate the susceptibility and magnetization of 200nm Fe particles in an applied 0.081T magnetic field. In order to evaluate their usefulness as magnetofection agents an antisense oligonucleotide designed to correct the aberrant splicing of enhanced green fluorescent protein mRNA was successfully attached to Fe Post-Particles via a polyethyleneimine linker and transfected into a modified HeLa cell line. [Preview Abstract] |
Thursday, October 30, 2008 10:06AM - 10:18AM |
BB.00009: Ligand induced ferromagnetism in ZnO nanostructures Qiang Sun, Qian Wang, Puru Jena We provide the first theoretical understanding of the origin of magnetism in ligated ZnO nanoparticles as well as the structural properties of the ligated systems by using density functional theory and generalized gradient approximation for exchange and correlation, and a cluster model for the nanoparticles. We show that N or S atoms of the ligand bind to the Zn sites. The accompanying changes in the ZnO bond length, hybridization between Zn 4s orbitals with N 2p or S 3p orbitals, and consequently the redistribution of charges between Zn and O atoms result in a magnetic system where the 2p electrons in O and N, and 3p electrons in S sites are spin polarized. Furthermore, the sites nearest to the Zn atom attached to the ligand carry bulk of the magnetic moment. Studies, as a function of cluster size, also illustrate that magnetism resides only on the surface. Our results confirm that use of ligands can pave a new way for introducing magnetism in ZnO nanostructures, which can be used to develop magnetic sensors to detect N and S containing molecules. [Preview Abstract] |
Thursday, October 30, 2008 10:18AM - 10:30AM |
BB.00010: The Constrained Crystallization of Nylon-6 Anushree Mohan, Alan Tonelli Non-covalently bonded crystalline inclusion compounds (ICs) have been formed by threading host cyclic starches, cyclodextrins (CDs) onto guest nylon 6 (N6) chains. When excess N6 is employed, non-stoichiometric (n-s)-N6-CD-ICs with partially uncovered and dangling N6 chains result. While the crystalline CD lattice is stable to $\sim $300\r{ } C, the uncovered and dangling, yet constrained, N6 chains may crystallize below or, as shown below, be molten above $\sim $225\r{ } C. We have been studying the constrained crystallization of the dangling N6 chains in (n-S)-N6-CD-ICs, with comparison to bulk N6 samples, as a function of N6 molecular weights, lengths of uncovered N6 chains, and the CD host used. In the IC channels formed with host $\alpha $- and $\gamma $-CDs containing 6 and 8 glucose units, respectively, single and pairs of side-by-side N6 chains are threaded and included. In the $\alpha $-CD-ICs the $\sim $ 0.5 nm channels are separated by $\sim $ 1.4 nm, while in $\gamma $-CD-ICs the $\sim $ 1 nm channels are $\sim $ 1.7 nm apart, with each $\gamma $-CD channel including 2 N6 chains. N6 chains in the bulk and in the dense (n-s)-N6-CD-IC brushes show distinctly different kinetic and thermodynamic crystallization behaviors. [Preview Abstract] |
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