Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session D43: Synthesis and Growth of Nanostructured Materials |
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Sponsoring Units: DCMP Chair: Chris Palmstrom, Univeristy of Minnesota Room: Colorado Convention Center 506 |
Monday, March 5, 2007 2:30PM - 2:42PM |
D43.00001: Detailed Structure Determination of Nanostructures by Low-Energy Electron Diffraction. Michel Van Hove, G.M. Gavaza, Z.X. Yu, L. Tsang, C.H. Chan, S.Y. Tong Detailed structural information of nanostructures (e.g. bond lengths and bond angles) is needed to allow the understanding and prediction of their physical and other properties. To that end we have extended the theoretical capabilities of surface structure determination by Low Energy Electron Diffraction (LEED) to nanostructures. Our new computational method has a compute time that scales as NlogN in terms of the number N of independent atoms, in contrast to N$^{2}$ or N$^{3}$ which typical of conventional LEED calculations of electron multiple scattering. We exhibit the resulting ability to solve detailed nanostructures of different kinds: buckyballs adsorbed on a Cu(111) surface; endohedral and exohedral buckyballs with additional Li or Cu atoms; adsorbed carbon nanotubes; and silicon nanowires. This demonstration of the capability to solve nanostructures should spur the development of experimental methods to measure electron diffraction from nanostructures. [Preview Abstract] |
Monday, March 5, 2007 2:42PM - 2:54PM |
D43.00002: Modeling the Role of Ligands in Controlling the Sizes, Shapes and Supramolecular Ordering of Quantum Dots Michael Tambasco, Sanat Kumar, Igal Szleifer The density of electronic states controls many physical properties of a quantum dot and can be tuned by altering the dot's size, shape, or composition. In colloidal methods, ligands are used to control quantum dot size, shape, and polydispersity; however, there exists no a-priori means of describing specific conditions that will optimize the synthesis procedure. We apply a mean field theory to study the role of ligands in quantum dot synthesis with particular emphasis on non-spherical shapes. We examine the effects of ligand type and concentration on thermodynamic and structural properties, and compare our results with available data. [Preview Abstract] |
Monday, March 5, 2007 2:54PM - 3:06PM |
D43.00003: Migration-influenced island size distribution in interfacial growth Da-Jun Shu, Mu Wang By considering island migration, island interaction and temperature, we demonstrate that distribution of both island size and spatial dispersion on surface can be tuned. It is shown that at lower temperature and stronger inter-island interaction, a narrow size distribution is accompanied by spatial uniformity when island migration is free; yet both size and spatial distribution become random when island migration is forbidden. At higher temperature and weaker inter-island interaction, however, entropy effect dominates, and a narrow size distribution is associated with a fluctuant spatial distribution when island migration is forbidden. These unexpected features are enlightening to fabricate quantum dots where uniformity in both size and spatial distributions are essential. [Preview Abstract] |
Monday, March 5, 2007 3:06PM - 3:18PM |
D43.00004: A level-set method for self-organized pattern formation during heteroepitaxial growth Christian Ratsch, Young-Ju Lee, Xiaobin Niu, Russel Caflisch We have developed an island dynamics model for heteroepitaxial growth that employs an island dynamics model with the level-set technique in combination with a fully self-consistent elastic model. At every timestep in the simulation, we solve the elastic equations for the entire system. This is possible within our approach because the numerical timestep can be chosen much larger than in an atomistic simulation. At every lattice site strain then changes the local bonding, and thus the potential energy surface for adatoms and the microscopic parameters of the simulation. In particular, strain changes the diffusivity of adatoms and enhances the rate of detachment from island edges. We will show how islands become smaller and more regular upon increasing strain. The reason is that bigger islands are typically more strained than smaller islands, and thus their growth is slowed down. We also present results that show that strain moves the system from layer-by-layer growth to the formation of coherent islands as a mechanism for strain relieve. [Preview Abstract] |
Monday, March 5, 2007 3:18PM - 3:30PM |
D43.00005: Phononic Band Gaps in Colloidal Crystals at Hypersonic Frequencies George Fytas, Wei Cheng, Eugenia Nunez, Ulrich Jonas, Nikolaos Stefanou The phononic properties of fabricated closed packed fcc colloidal crystals were investigated by high resolution Brillouin light scattering spectroscopy in the GHz frequency range. The dispersion relation has revealed two phononic band gaps: (i) a Bragg --gap occurring at the boundary of the first Brillouin zone and (ii) a hybridization-gap resulting from the interaction of particle eigenmodes with the acoustic mode of the effective medium. Crystallinity is a prerequisite for the appearance only of the Bragg-gap. Depending on the particle size and the speed of sound in the infiltrated fluid, the frequency and the width of the Bragg-gap can be tuned. Since hypersonic crystals can simultaneously exhibit phononic and photonic band gaps in the visible spectral region, the technological applications could range from tunable filters and heat management to acoustic-optical devices. [Preview Abstract] |
Monday, March 5, 2007 3:30PM - 3:42PM |
D43.00006: Local crystal structure of iron oxide nanoparticles synthesized from Ferritin Michael Krispin, Marcus Preisinger, Peter Pfalzer, Siegfried Horn, Daniel Strongin We have investigated the size dependence of the local crystal structure of nanosized iron oxide by extended x-ray absorption fine structure (EXAFS) at the iron K-edge. Hematite ($\alpha $-Fe$_{2}$O$_{3})$ nanoparticles of different diameters were produced by thermal treatment of horse spleen ferritin molecules and remineralized apo-ferritin molecules, respectively. The structure of these particles was compared to $\alpha $-Fe$_{2}$O$_{3}$ and $\gamma $-Fe$_{2}$O$_{3}$ nanopowder references. The Fourier transformed EXAFS spectra of the nanoparticles differ significantly from hematite and maghemite reference spectra and change systematically as a function of particle diameter, signalling a corresponding evolution of the structure. We show that the Fe--O bond length decreases with decreasing diameter of the particles and with decreasing particle density. This is explained by a core-shell model, in which the fraction of a $\gamma $-Fe$_{2}$O$_{3}$ like particle shell increases while the hematite core decreases with decreasing particle size. [Preview Abstract] |
Monday, March 5, 2007 3:42PM - 3:54PM |
D43.00007: Viscoplasticity and granularity in films of colloidal nanocrystals Dongyun Lee, Shengguo Jia, Sarbajit Banerjee, Joze Bevk, Irving Herman, Jeffrey Kysar Thin films composed of colloidal CdSe nanocrystals have been electrophoretically deposited onto Au/Si substrates with thicknesses ranging from 300 to 3200 nm. The mechanical properties of these films have been measured by nanoindentation. Indentation is carried out to 25{\%} of total thickness of the films, and the elastic modulus and hardness of the films are measured at 10{\%} of the total film thickness to minimize substrate effects. In addition, the force is held at peak load for up to 20 s to observe the creep behavior of the films. The elastic modulus and hardness of 3.2 nm nanocrystal films are $\sim $10 GPa and $\sim $450 MPa, respectively. Furthermore, after particle cross-linking and partial ligand removal, the films exhibit compaction of the cores. This mechanical response suggests these nanocrystal films have polymeric features that can be attributed to the organic ligands and granular characteristics due to the inorganic cores. Both characteristics have also been confirmed by investigating larger nanocrystals and by removing the capping ligands. This work was supported primarily by the MRSEC Program of the NSF under Award No. DMR-0213574 and by NYSTAR. Nanoindentation studies at the Oak Ridge National Laboratory SHaRE User Center were sponsored under DE-AC05-00OR22725. [Preview Abstract] |
Monday, March 5, 2007 3:54PM - 4:06PM |
D43.00008: Doping colloidal nanocrystals: the role of surfactacts Mao-Hua Du, Steven Erwin, Alexander Efros The intentional doping of nanocrystals (NCs) with impurity atoms will be critical to their functioning in a variety of technologies. For NCs grown by colloidal synthesis, doping efforts have been far less successful than for their bulk counterparts. We recently proposed a theoretical model that explains this difference [1]. The central idea is that because the temperatures used in colloidal growth are low (250-300 C), thermal equilibrium is never established. Instead, kinetic factors -- such as impurity adsorption on the NC surface -- play a dominant role in dopant incorporation. Here we consider another kinetic factor known to strongly affect doping in colloidal NCs: the surfactant molecules that are added to passivate the growing NC. We show that the binding strength between the surfactant and dopants in solution strongly affects the dopant sticking coefficient on the NC surfaces, and the dopant solubility in solution. We focus on Mn doping of CdSe NCs, and use first-principles calculations to shed light on the competition between dopant-surface, surfactant-surface, and dopant-surfactant interactions. Our findings are consistent with experimental results for Mn incorporation in CdSe NCs. [1] S.C. Erwin, L. Zu, M.I. Haftel, Al.L. Efros, T.A. Kennedy, and D.J. Norris. Doping semiconductor nanocrystals. Nature \textbf{436}, 91 (2005). [Preview Abstract] |
Monday, March 5, 2007 4:06PM - 4:18PM |
D43.00009: ABSTRACT WITHDRAWN |
Monday, March 5, 2007 4:18PM - 4:30PM |
D43.00010: Sub-100 nm interferometric lithography realized with table top extreme ultraviolet lasers Mario Marconi, Przemyslaw Wachulak, Dineshchandra Patel, Maria Gabriela Capeluto, Carmen Menoni, Jorge Rocca We demonstrated patterning of arrays of nano-dots with feature sizes below 100 nm by interferometric lithography using a table top extreme ultraviolet 46.9 nm wavelength laser. The interferometric lithography setup was based on a Lloyd's mirror interferometer and multiple exposures. That allowed the patterning of arrays of nano-dots over areas of 500$\times $500 $\mu $m$^{2}$ on commercial photoresists with different motifs. This new technique demonstrates the printing capability of nano-scale patterns with a compact table-top set up at extreme ultraviolet wavelengths. [Preview Abstract] |
Monday, March 5, 2007 4:30PM - 4:42PM |
D43.00011: Chemical Nanomachining of Si Jeremy Robinson, Paul Evans, J. Alex Liddle, Oscan Dubon We demonstrate a simple process for chemical nanomachining of reproducible Si nanonstructures. Using a stencil mask containing windows of various geometries, we evaporate Au onto a Si surface rinsed in HF. The pattern formed by the spontaneous oxidation of Si at and around each patterned Au feature serves as a mask for the underlying Si and permits the use of simple wet chemistry to produce highly ordered nanostructures of diverse shapes including rings, pillars, wires, and nanopores. Pillars are formed by etching a Si sample patterned with an array of nominally 1 nm-thick Au squares having a side dimension of 200 nm. Remarkably, the Au capped core of these pillars can be removed by briefly rinsing the Au-patterned sample with HF prior to etching with KOH. When the Au-squares are sufficiently close together, the anodic oxide patterns surrounding the Au squares overlap to form a continuous surface oxide. Etching in this case with HF followed by KOH produces a continuous Si film with holes. Thus, this unique catalyzed patterning process opens the door for the rapid, parallel fabrication of a variety of nanostructures that are unfeasible or impractical to fabricate with traditional processing routes. [Preview Abstract] |
Monday, March 5, 2007 4:42PM - 4:54PM |
D43.00012: Sculpting of Nanopores in Silicon-Nitride Membranes Kristin Lucas, Jeffrey L. Wasserman, Soo Hyung Lee, Nina Markovic Fabrication of controllable-diameter nanopores in a suspended membrane is of great interest for dynamic stencil deposition techniques, as well as DNA sequencing and other applications. We have developed a method for the production of nanometer-scale pores in a silicon-nitride membrane. We punch holes in a membrane of low-stress silicon-nitride through focused ion beam or lithographic techniques. By exposing the holes to an electron beam we can shrink the pore diameter down to a few nanometers. We can also produce complex pore shapes through selective sculpting of the pore. We will discuss the details of the process and its applications. [Preview Abstract] |
Monday, March 5, 2007 4:54PM - 5:06PM |
D43.00013: Nanocrystalline Composite Media in the GeO$_{2}$-Ga$_{2}$O$_{3}$ Mullite-Type System: Synthesis and Conventional as Well as Synchrotron Based Characterization Kristina E. Lipinska-Kalita, Patricia E. Kalita, Oliver Hemmers, Cedric L. Gobin, Gino Mariotto, Thomas Hartmann, Longzhou Ma In the frame of our extensive project on nanocomposites based on dielectric matrices, we designed and synthesized a series of optically transparent glass-based composites, containing nanometer-sized crystals embedded in an isotropic host matrix. We determined the structure of the nanocrystals to be an orthorhombic GeO$_{2}$-Ga$_{2}$O$_{3}$ mullite-type phase, isostructural with SiO$_{2}$-Al$_{2}$O$_{3}$ mullite. In order to characterize the materials synchrotron X-ray diffraction, optical spectroscopy and electron microscopy were used. High-pressure compression and decompression studies up to 40 GPa were also performed to investigate the structural integrity of the nanocrystals. This work is the first report of a controlled, successful synthesis of Ge-Ga mullite type nanocrystalline composites. [Preview Abstract] |
Monday, March 5, 2007 5:06PM - 5:18PM |
D43.00014: GaAs$_{x}$P$_{1-x}$ Superlattice nanowires. Romaneh Jalilian, Sharvil Desai, Anton Sidorov, Zhiqiang Chen, B. K. Pradhan, Gamini Sumanasekera Semiconductor alloys provide a natural tool to tune the bandgap by managing the spatial spreading and distribution of alloys sequentially along a nanowire. A growth technique has been developed using laser ablation to synthesize ternary alloys of GaAs$_{x}$P$_{1-x}$ superlattice nanowires. These superlattice nanowires exhibit very interesting structures; alternating crystalline structures of GaAs$_{x}$P$_{1-x }$alloys grow in one direction. Continuous modulation of growth routine, specially the ablation time can control the composition of the segments in the superlattice nanowires. SEM, HRTEM, SAD, EDS, EELS, XRD, XPS have been used to study the morphology, crystalline structures and relative distribution of gallium, arsenic and phosphorus in ternary alloys superlattice. Optical absorption, luminescence and electrical properties have been explored. [Preview Abstract] |
Monday, March 5, 2007 5:18PM - 5:30PM |
D43.00015: Quantitative structural characterization of annealed InAs/GaSb superlattices Ge Liu, Bernd Fruhberger, Ivan K. Schuller, Heather J. Haugan, Gail J. Brown MBE grown InAs/GaSb superlattices without \textit{in situ} thermal processing were post-growth annealed in vacuum and analyzed by a combination of XRD and structural refinement. The refinement shows a FWHM of satellite peak broadening and a d-spacing contraction in InAs constituent layers, which are caused by interfacial roughness and inhomogeneous strain, when the annealing temperature is above 200 $^{o}$C. Furthermore, the annealing above 450 $^{o}$C destroys the superlattice structure and annihilates all satellite peaks. An additional series of satellite peaks showing InSb-like behavior was found in annealed superlattices which is reduced by further annealing at 200 $^{o}$C. The refinement reveals that these peaks arise from the ``superlattice'' composed of InSb-like structure. The surface morphology studied using AFM shows that the InAs/GaSb superlattice surfaces evolve from flat plane, porous structure, and pebble structure to island structure as the annealing temperature increases. [Preview Abstract] |
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