Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session X34: Nanostructures: Assembly, Growth, and Characterization |
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Sponsoring Units: DCMP Chair: Eric Stinaff, Ohio University Room: C141 |
Thursday, March 24, 2011 2:30PM - 2:42PM |
X34.00001: Vapor-Liquid-Solid Glancing Angle Deposition (VLS-GLAD): A New Approach to Fabricate Crystalline Semiconductor Nanowires Arif Sinan Alagoz, Tansel Karabacak Vapor-liquid-solid (VLS) method has become one of the few and most powerful bottom-up single crystal nanowire growth techniques. On the other hand, control of growth direction and crystal orientation of semiconductor nanowires stand as major issues in VLS technique. In order to overcome these challenges, we developed a new vapor-liquid-solid glancing angle deposition (VLS-GLAD) fabrication approach for the growth of semiconductor nanowire arrays with a controlled geometry and crystal orientations. VLS-GLAD is a physical vapor deposition nanowire fabrication approach based on selective deposition of nanowire source atoms onto metal catalyst nanoislands placed on a crystal wafer. In this technique, collimated obliquely incident flux of source atoms selectively deposit on catalyst islands by using ``shadowing effect''. Geometrical showing effect combined with conventional VLS growth mechanism leads to the growth of tilted crystalline semiconductor nanowire arrays. In this presentation, we show the morphological and structural properties of tilted single crystal Si and Ge nanowire arrays fabricated by utilizing a conventional thermal evaporation system for VLS-GLAD. [Preview Abstract] |
Thursday, March 24, 2011 2:42PM - 2:54PM |
X34.00002: LEEM and STM observations of Growth of Nanowires of Ag on Ge(110) and Surface Structural Phases of Ir on Ge(111) Cory Mullet, Marshall van Zijll, Emilie Huffman, Shirley Chiang We have used both low energy electron microscopy (LEEM) and scanning tunneling microscopy (STM) to characterize the growth of silver on Ge(110) and iridium on Ge(111) as a function of coverage, deposition temperature, and annealing temperature. We observed 1D island growth along [-110] as Ag is deposited onto Ge(110) above 430 C. Island dimensions varied with deposition temperature. At 480 C, Ag islands are $\sim $100nm wide and 1-20 $\mu $m long for 9 ML coverage. Between 380 C and 430 C, we observed two novel low coverage phases, with the higher coverage phase completing at 0.12 ML. Ir deposited onto the Ge(111) c(2x8) above 400 C forms a ($\surd $3x$\surd $3)R30$^{o}$ phase, with island size dependent upon substrate temperature during deposition. Deposition at 400-425 C produces Ir islands, which are 1-20 nm in diameter at 0.5 ML coverage. Island heights range from one to several atomic layers, and exhibit a unique growth mode with islands connected by ``streamers'' of Ir. We observed Stranski-Krastanov growth in LEEM at 670 C. Ir desorbs from Ge(111) at 870 C, beginning from areas of high step density. [Preview Abstract] |
Thursday, March 24, 2011 2:54PM - 3:06PM |
X34.00003: ABSTRACT WITHDRAWN |
Thursday, March 24, 2011 3:06PM - 3:18PM |
X34.00004: Alignment of Gold Nanorods in Thermoresponsive Hydrogels Heung-Shik Park, Oleg Lavrentovich The unique optoelectronic properties of the anisotropic metallic nanorods (NRs) are of great interest because of their potential applications in biomedical science, transformative optics and materials science. In order to utilize metallic NRs for the practical devices, the control of orientation and immobilization of NRs in bulk materials are essential. We report an experimental study of gold NR embedded in thermoresponsive gels which can align NRs by volume-contraction transition. When temperature increases, an NR hydrogel stripe experiences an abrupt shrinkage in two lateral (x,y) directions; in the third z-direction, the size remains fixed as the stripe is clamped. The shrunk stripes show high birefringence and anisotropic absorption associated with alignment of the NRs. The alignment of NRs in anisotropically shrunk hydrogels can be achieved also when one uses aggregates of side-by-side preassembled NRs rather than individual NRs. These aggregates can be transferred into a polymer hydrogel preserving their structural and optical features. The hydrogel stripes with preassembled NRs show optical anisotropy opposite to that one of stripes with isolated NRs. [Preview Abstract] |
Thursday, March 24, 2011 3:18PM - 3:30PM |
X34.00005: Programmable Nanofabrication of Nanoparticle Assemblies of arbitrarily Shapes on DNA Templates Mauricio Pilo-Pais, Sarah Goldberg, Enrique Samano, Henok Mebrahtu, Thomas LaBean, Gleb Finkelstein We present a method for producing metallic structures with nanoscale dimensions and programmable design. Rectangular ``DNA origami'' structures ($\sim $90x70nm) were modified to have uniquely coded binding sites and adsorbed onto silicon dioxide substrates. Gold nanoparticles functionalized with a complimentary DNA sequence were attached to these binding sites in a highly controllable fashion. The seed nanoparticles were then enlarged (and even fused, if desired) by a silver reduction chemistry. Using this method we constructed a variety of metallic structures, including parallel wires, H-shapes, and rings. Due to the flexibility of the design and the multiply parallel nature of the method, these structures may offer great promise for plasmonic applications. [Preview Abstract] |
Thursday, March 24, 2011 3:30PM - 3:42PM |
X34.00006: Controlling Nanostructure Self-assembly for Design of Three-dimensional Semiconductor Heterostructures Santino D. Carnevale, J. Yang, P.J. Phillips, M.J. Mills, R.C. Myers We examine the control of vertical and coaxial growth in self-assembled GaN/AlN nanowires grown on Si (111) by plasma assisted molecular beam epitaxy. To grow nanowires vertically and not radially a two-step growth method is used. Nanowires are nucleated at low temperatures and grown vertically at high temperatures, allowing for independent control of density and height and constant radius. A second method is used to promote radial growth. GaN nanowire cores are formed, then growth temperature is reduced and growth continues. Vertically and coaxially oriented AlN/GaN heterostructures grown using these methods are presented. We discuss the structural and optical properties of these GaN/AlN quantum disk and core-shell heterostructures using scanning electron microscopy, scanning transmission electron microscopy, and temperature dependent photoluminescence measurements. [Preview Abstract] |
Thursday, March 24, 2011 3:42PM - 3:54PM |
X34.00007: Preparation of monodisperse silicon nanocrystals through density-gradient unltracentrifugation in organic solvents Joseph B. Miller, Austin Van Sickle, Swathi Iyer, Rebecca A. Anthony, Uwe R. Kortshagen, Erik K. Hobbie Monodisperse colloidal suspensions of ligand-coated silicon nanocrystals, synthesized through a nonthermal low-pressure plasma reaction, have been prepared through density-gradient ultracentrifugation in mixed organic solvents. Density-gradient profiles of mixed chloroform and m-xylene are used to tune and control the settling speed of the nanoparticles and hence optimize their transient separation by size along the depth of polyoxymethylene ultracentrifuge tubes. The mean size and polydispersity of the extracted fractions are characterized through photoluminescence spectroscopy and transmission electron microscopy, and the self-assembly of fractions into close-packed crystal lattices is achieved using an immiscible two-fluid evaporation scheme. The photophysical properties of the nanocrystal lattices are compared with those of the starting materials and suspensions, and the influence of atmospheric oxygen on the stability of the nanocrystal photoluminescence is measured. [Preview Abstract] |
Thursday, March 24, 2011 3:54PM - 4:06PM |
X34.00008: Self-assembled Au Nanoparticle Arrays with Engineered Hot Spots for SERS A. Chen, U. Welp, V. Vlasko-Vlasov, A.E. DePrince III, A. Demortiere, A. Joshi-Imre, E.V. Shevchenko, S.K. Gray We demonstrate a cost-effective bottom-up self-assembly of 80 nm Au nanoparticles (NPs) with controllable regular arrays of hot spots for high-fidelity and high-sensitivity sensor applications. The self-assembly of gold NPs is implemented using solvent evaporation techniques. By careful control of surface stabilizers on NPs and optimization of assembly conditions, we fabricated hcp arrays of NPs extended over more than 200 $\mu$m. Electromagnetic hot spots localized in the nanometer gaps between Au NPs are well defined and reproducible over large areas of the arrays. UV-Vis-NIR extinction spectra of our 2D plasmonic crystals exhibit unique resonances due to strong particle-particle interactions, in a good agreement with results of our finite-difference-time-domain (FDTD) simulations. We experimentally demonstrate large enhancements of both photoluminescence and surface enhanced Raman scatterings of 5nm CdSe quantum dots coated on 80nm Au NP arrays. High-resolution SEM imaging of quantum dots gave a precise estimate of their density and positions and allowed direct evaluation of the enhancement factors. [Preview Abstract] |
Thursday, March 24, 2011 4:06PM - 4:18PM |
X34.00009: Fine tuning nanoparticle spacing in freestanding membranes through ion and electron beams Pongsakorn Kanjanaboos, Alexandra Joshi-Imre, Xiao-Min Lin, Heinrich Jaeger Freestanding membranes of ligated nanoparticles can be assembled in a one-step drying-mediated process. These 2D sheets have remarkable mechanical properties, in particular extreme bending flexibility coupled with effective Young's moduli in the range of 1-20GPa, depending on the nanoparticle and ligand types and sizes. We report on experiments in which used a focused Ga ion beam to strategically place cuts into freestanding monolayer membranes. Exposed to electron beams, the cuts expand and the membranes act as if additional strains were deposited. Given that the exposed membranes behave like strained elastic sheets, we can easily design various strain patterns. With calibration, the electron beam dose serves as a knob to fine-tune interparticle distances in these patterns. \\ K. E. Mueggenburg, X. Lin, R. H. Goldsmith, and H. M. Jaeger, Nature Materials 6, 656 (2007). J. He, P. Kanjanaboos, N. L. Frazer, X. Lin, and H. M. Jaeger, Small 6, 1449 (2010) W. Cheng et al. Nature Materials 8, 519 (2009) [Preview Abstract] |
Thursday, March 24, 2011 4:18PM - 4:30PM |
X34.00010: Mechanics of colloidal nanoparticle arrays Jie Yin, Markus Retsch, Edwin L. Thomas, Mary C. Boyce Hollow colloidal nanoparticles have become a focal point of studies for applications in drug delivery and nanostructured materials. The mechanical properties of individual nanoparticle and the collective behavior of colloidal nanoparticle arrays are of great importance. In this paper, the mechanics of colloidal arrays of hollow amorphous silica spherical nanoparticles during microindentation are explored. The study reveals that the consecutive contact process of nanoparticles during indentation results in highly nonlinear indentation load-displacement curves. The contacted nanoparticles successively become flattened and locally bend and buckle to form a localized dimple as the indentor encounters each particle. By using the contact mechanics model of single hollow particle, the indentation load-displacement formula is obtained for indentation on hollow spherical nanoparticle arrays and the Young's modulus of an individual particle is extracted from the measured load-displacement behavior of an array. The reduced Young's modulus is consistent with the measurement of single hollow amorphous silica nanoparticle by using AFM. [Preview Abstract] |
Thursday, March 24, 2011 4:30PM - 4:42PM |
X34.00011: Au/Fe nanoparticles prepared by multilayers annealing Aida Serrano, Oscar Rodriguez de la Fuente, Miguel Angel Garcia Metallic nanoparticles supported onto a substrate can be obtained by thin film deposition and subsequent annealing. The stress relief after the thermal annealing due to the difference of thermal expansion coefficient between the metal and the substrate promotes hillock formation and subsequent hole nucleation, growth and percolation leading to the formation of nanoparticles layers. The nanoparticle size and inter-particle distance can be tuned by controlling the initial film thickness and the annealing time, temperature and atmosphere, providing a simple and low cost method to prepare NPs layers over large areas. The method has been successfully applied to obtain nanoparticles from a single metallic layer in the past. We report here the formation of complex nanoparticles ensembles by deposition and annealing of Au-Fe multilayers. The optical properties of gold nanoparticles (surface plasmon resonance absorption) and the magnetic properties of Fe/Fe oxide ones as well as cross-over effects are studied as a function of multilayers structure and annealing conditions. [Preview Abstract] |
Thursday, March 24, 2011 4:42PM - 4:54PM |
X34.00012: Effects of ligand binding strength and facet coverage on the morphology of nanocrystal superlattices Clive Bealing, Richard Hennig Nanocrystals (NCs) of lead-salt have been proposed for a number of photovoltaic applications. These NCs consist of an inorganic core, in the rock salt structure, whose surface is usually passivated by oleate ligands. The self-assembly of NCs from colloidal solutions into mesoscale superlattices provides a path to materials with tunable electronic, physical and chemical properties that are promising for applications. The self-assembly is controlled by the NC shape and by ligand-mediated interactions between NCs; to understand this, it is necessary to know the effect of the ligands on the surface energies, as well as the relative coverage of the different facets. Our density functional calculations of the binding energies of carboxylic acid-based ligands on PbSe and PbS show that the ligands exhibit a strong energetic preference to particular facets. The results suggest that the transformation of the NC superlattice structure from \emph{fcc} to \emph{bcc} in aged NC assemblies is caused by the preferential detachment of ligands from particular facets, leading to anisotropic ligand coverage. Combined with the experimental results, our calculations present a potential route to greater control over the morphology of the NC superlattice assembly. [Preview Abstract] |
Thursday, March 24, 2011 4:54PM - 5:06PM |
X34.00013: Scanning Tunneling Microscopy and Spectroscopy of Rare Earth-Monopnictide Nanostructures Embedded in a Semiconducting Matrix Jason Kawasaki, Rainer Timm, Trevor Buehl, Edvin Lundgren, Anders Mikkelsen, Arthur Gossard, Chris Palmstr{\O}m The atomic and electronic structure of molecular beam epitaxy (MBE)-grown rare earth-monopnictide nanostructures embedded within a III-V semiconductor matrix are examined via scanning tunneling microscopy (STM) and spectroscopy (STS). We examine several systems, including ErSb nanoparticles embedded in GaSb, ScAs nanoparticles embedded in GaAs, and ErAs nanoparticles and nanorods embedded in GaAs. Tunneling current I(V) and differential conductance dI/dV spectra show that for both ErAs nanoparticles and nanorods the local density of states (LDOS) exhibits a sharp but finite minimum at the Fermi level, demonstrating that both the particles and rods are semimetallic and not semiconducting. This observation lies in contrast to previous models of quantum confinement in ErAs. We also use STS to measure the LDOS across the ErAs/GaAs interface and discuss the formation of interface states and band bending at the interface. Finally, we discuss possible changes in the LDOS with varying nanoparticle size and varying levels of doping in the semiconductor matrix. [Preview Abstract] |
Thursday, March 24, 2011 5:06PM - 5:18PM |
X34.00014: \textit{Ab Initio }Studies of Si$_{m}$Ge$_{n }$(m+n $\leq$ 5) Nanoclusters Sarah Duesman, Asok Ray Electronic and geometric structure properties of Si$_{m}$Ge$_{n}$(m+n $\leq$ 5) nanoclusters have been investigated using hybrid density functional B3LYP, 6-311G (3df, 3pd) basis set, and the GAUSSIAN 03 software. For the Si atom, the computed values of the ionization potential and electron affinity are 8.11 and 1.10eV, and for the Ge atom, the values are 7.90 and 1.14eV. The experimental values are 8.15, 1.39, 7.90, and 1.23eV, respectively. Various possible geometries have been spin-optimized to determine the global minimum for each nanocluster. We will present the electronic and geometric structures of the isomers of each nanocluster, including bond length, symmetry group, electronic state, binding energy, HOMO-LUMO gap, ionization potential, and electron affinity. In addition, the harmonic frequencies, fragmentation energies, average coordination number and Mulliken atomic charges will also be discussed for the ground states of the nanoclusters. [Preview Abstract] |
Thursday, March 24, 2011 5:18PM - 5:30PM |
X34.00015: Competition of Nonlinear Optical Properties in ZnO Nanoparticles Jie Lin, Antonio Llopis, Benny Urban, Yasuhisa Fujita, Arup Neogi ZnO nanoparticles have attracted increased attention due to its large exciton binding energy. Moreover it has enhanced nonlinear optical properties due to its noncentrosymmetric crystal structure which results in a second order nonlinearity. The presence of oxygen vacancy and modified surface states also yields third order nonlinearity such as two photon absorption which yield significant two-photon emission. However, the presence of high second order nonlinearity in a system can result in the retardation of the third order nonlinearity. We thereby present the relative efficiencies of the second and the third-order nonlinear processes in ZnO nanoparticle system. Using tunable femtosecond laser irradiation the recombination lifetime due to single and two-photon induced electron-hole recombination process has been studied. Our results show that the second harmonic generation (SHG) process compete with the two photon emission(TPE) process in the region 700nm---900nm. The TPE process is more efficient in 700 nm-740nm whereas the SHG process is more efficient from 745-900nm) region. We also observed the increase of the two photon emission with excited energy is caused by the increased life of its virtual state. [Preview Abstract] |
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