Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session V9: Self Assembly I |
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Sponsoring Units: DFD Chair: Steve Granick, University of Illinois at Urbana-Champaign Room: D220 |
Thursday, March 24, 2011 8:00AM - 8:12AM |
V9.00001: Effects of cluster diffusion on the island density and size-distribution in submonolayer island growth Yevgen Kryukov, Jacques Amar The effects of cluster diffusion on the submonolayer island density and island-size distribution (ISD) $N_s(\theta)$ (where $N_s(\theta)$ is the number of islands of size $s$ at coverage $\theta$) are studied for the case of irreversible submonolayer growth of compact islands on a 2D substrate. In our model, monomers are deposited with deposition rate $F$ while the mobility $D_s$ of an island of size $s$ satisfies $D_s \sim s^{-\mu}$. Results are presented for $\mu = 1/2$ (corresponding to Brownian motion) as well as for higher values of $\mu$. In general, we find that the exponents describing the flux-dependence of the island and monomer densities vary continuously as a function of $\mu$. For $\mu < 1$ we also find that the ISD exhibits power-law behavior up to a cross-over size $S_c$. However, the values of the corresponding exponents are significantly larger than previous theoretical predictions. A generalized scaling form for the ISD for $\mu < 1$ is also proposed which leads to excellent scaling of the entire distribution. In contrast, for $\mu \ge 1$ we find that, due to a competition between size-scales, neither our generalized scaling form nor the standard scaling form $N_s(\theta) = \theta/S^2~f(s/S)$ (where $S$ is the average island-size) lead to scaling of the entire ISD. Instead, the scaled ISD becomes more sharply peaked with increasing $D_1/F$ and coverage. This is in contrast to models with limited cluster mobility for which good scaling occurs over a wide range of coverages and $D_1/F$. [Preview Abstract] |
Thursday, March 24, 2011 8:12AM - 8:24AM |
V9.00002: Rate-equation approach to irreversible island growth with cluster diffusion Bradley Hubartt, Yevgen Kryukov, Jacques Amar A self-consistent rate-equation (RE) approach to irreversible island growth and nucleation is presented which takes into account the effects of cluster mobility. As a first application we consider the irreversible growth of compact islands on a 2D surface in the presence of monomer deposition (with rate $F$) and monomer diffusion (with rate $D_1$) while the mobility of an island of size $s$ is assumed to satisfy $D_s = D_1 s^{-\mu}$ where $\mu \ge 0$. For coverages up to the peak island-density, we find excellent agreement between our RE and simulation results for the dependence of the island-density $N(\theta)$ on coverage $\theta$ for all values of $\mu$ considered, ranging from $\mu = 1/2$ (Brownian motion) to $\mu = \infty$ (immobile clusters). For $\mu \le 2$, excellent agreement is also found between our simulation and RE results for the island-size distribution (ISD), while for higher values of $\mu$ the effects of correlations become important. We also demonstrate that the discrepancies between recent theoretical predictions for the exponents $\tau(\mu)$ and $\zeta(\mu)$ describing the size-dependence of the ISD for $\mu < 1$ and simulations can be explained by the geometry of compact islands. Our self-consistent RE approach may also be generalized to higher dimensions as well as to an arbitrary dependence of the cluster mobility on island-size. [Preview Abstract] |
Thursday, March 24, 2011 8:24AM - 8:36AM |
V9.00003: Kinetics and Thermodynamics of the Association of DNA Coated Colloids Kun-Ta Wu, Feng Lang, Ruojie Sha, Remi Dreyfus, Nadrian Seeman, Paul Chaikin We have investigated the aggregation kinetics and thermodynamics of complementary DNA coated particles as a function of DNA coverage. The streptavidin on our particles can accommodate 69800 biotinalated DNA which has 50 base pair double strands and 11 base sticky ends. For full 100\% coverage, the melting temperature, $T_m$, is 50.3 C. The transition width, $\Delta T$, is 0.8 C, and the characteristic aggregation time, $\tau$, is 4 minutes. For 2.5\% (40 times less) coverage $T_m$ = 22 C, $\Delta T$ = 5 C, and $\tau$ = 11 hours. A simple model which takes into account the number of DNA bonds and the multiplicity of their arrangements accounts for the full time and temperature dependence of the particle aggregation. [Preview Abstract] |
Thursday, March 24, 2011 8:36AM - 8:48AM |
V9.00004: DNA driven 2D Assembly of Nanoparticles on Lipid Surfaces Sunita Srivastava, Dmytro Nykypanchuk, Oleg Gang Use of biomolecular linkers such as DNA due to its sequence-specific hybridization properties provides a versatile platform for assembly of nanoscale components. Here we investigated the DNA-based self-assembly of gold nanoparticles in 2D using lipid layer as fluid substrate. We examined the effect of lipid composition by vary the fraction of cationic and zwitterion lipids on formation of a particle monolayer. Using in-situ X -ray reflectivity we observed adsorption of DNA functionalized nanoparticles on charged lipid surfaces. The surface density of the particle monolayer can be tuned by changing the electrostatic interaction between the particles and the lipid surface. The in-situ measured particle desorption from the lipid surface due to a change of a salt concentration provides quantitative information on particle-surface interactions. The ex-situ studies on samples using XPS under similar conditions support our observations. Our studies explore the possibility to form regulated 2D systems, as well as provide basic understanding of interactions of charge nano-objects with lipids, which is important for the biomedical applications. [Preview Abstract] |
Thursday, March 24, 2011 8:48AM - 9:00AM |
V9.00005: Computational Analysis of DNA-Mediated Crystallization of Binary Colloidal Superlattices Talid Sinno, Raynaldo Scarlett, Marie Ung, John Crocker Colloidal self-assembly provides a potential avenue for the design of novel devices with unique optical and structural properties. Colloidal systems also provide useful insights into fundamental mechanisms of phase transitions such as crystal nucleation, growth and melting that are otherwise difficult to probe in atomic systems. A promising approach for realizing highly tunable colloidal assembly is to graft single-stranded DNA oligomer brushes onto the surfaces of particles in order to create attractive interactions between them. Using this approach, micro- and nanoscale particles have now been successfully assembled into several crystalline phases, including ordered, binary superlattice structures. Here, we apply Monte Carlo simulations and free energy calculations to generate a detailed picture for the assembly binary superlattice crystals. The interparticle potential used to perform the calculations was generated specifically for DNA-mediated interactions and verified by measurements. We develop a pseudo-phase diagram for the binary superlattice system which includes both thermodynamic and kinetic influences. The predictions of the pseudo-phase diagram are validated using direct simulations of crystal nucleation. Finally, we discuss recent findings related to diffusionless transformations in growing superlattice crystals that may be important in experiments aimed at growing these structures. [Preview Abstract] |
Thursday, March 24, 2011 9:00AM - 9:12AM |
V9.00006: DNA Linker Mediated Assembly of Gold Nanoparticles Superlattice Huiming Xiong, Mattew Y. Sfeir, Daniel van der Lelie, Oleg Gang A BCC (body-centered-cubic) crystalline phase forms when flexible ssDNA linkers are added to the mixture of two types of dispersed, ssDNAs capped gold nanocolloids which are mutually non-complementary but complementary to the respective ends of the linker DNA. The state diagram of DNA linker mediated nanoparticle assemblies has been experimentally investigated and constructed by using in-situ small angle x-ray scattering. The optically active three-dimensional superlattice containing plasmonic particles and DNA-encoded chromophors were further fabricated using this approach. We investigated structural tunability and corresponding optical response of the multicomponent superlattices. [Preview Abstract] |
Thursday, March 24, 2011 9:12AM - 9:24AM |
V9.00007: Directed Self-Assembly of Colloidal Particles Zorana Zeravcic, Jesse Collins, Vinothan Manoharan, Michael Brenner In nature, simple constituents like atoms, molecules and polymer chains, spontaneously organize into larger, higher order structures. Interactions involved in this self-assembly act on a local level. These facts inspire experimental and theoretical engineering of components able to organize into pre-designed complex systems. We perform numerical simulations of collections of DNA coated colloidal particles. We test different design rules for self-assembly with short-range interactions and explore the stability of equilibrium structures. [Preview Abstract] |
Thursday, March 24, 2011 9:24AM - 9:36AM |
V9.00008: Replication of nanoscale DNA patterns Corinna Maass, Tong Wang, Ruojie Sha, Mirjam Leunissen, Remi Dreyfus, Nadrian Seeman, Paul Chaikin We present an artificial supramolecular system mimicking self- replication and information transmission strategies in nature, but without the aid of enzymes or equivalent biological mechanisms. Using DNA nanotechnology techniques, we can make DNA tiles with selective interactions based on complementary single-strand connections. A linear tile pattern distinguished by their connector sequences is transmitted to a subsequent generation of copies by connector hybridisation. Longitudinal pattern formation and transverse copy attachment are well separated by different melting temperatures. We have achieved a faithful transmission of the pattern information to the second replication generation. We use AFM imaging to test for pattern fidelity and gel electrophoresis for quantitative yield analysis. [Preview Abstract] |
Thursday, March 24, 2011 9:36AM - 9:48AM |
V9.00009: Designing colloids for alignment Remi Dreyfus, Tycho Sleator, Kenny Mayoral, Thomas G. Mason, Paul M. Chaikin Inducing the spontaneous association of microscopic building blocks into macroscopic structures has been a promising way to create new materials for a variety of useful applications. Such fabrication processes typically require interactions between microscopic building blocks. The interactions that govern the assembly of these microscopic building clocks: electrostatic, magnetic, Van der Waals, depletion, and DNA interactions, are all currently being investigated. For all these cases, the attractive energy between the particles is proportional to the overlapping surface between the colloids. Controlling the positions and orientations of the microscopic building blocks is a critical issue in such processes. To date there has been no efficient or reliable process that enables such spontaneous assembly of building blocks. For the successful alignment of any particles that we desire to self-assemble, a shape with unique physical and mathematical properties must be identified. Under the assumption that energy is reduced in proportion to area overlap, we present a geometrical shape which, when encountering a similar shape from any initial configuration, is forced into a single relative orientation maximizing the overlap. The unique minimum of energy in the energy landscape drives the particles to self-assemble in a controlled orientation. [Preview Abstract] |
Thursday, March 24, 2011 9:48AM - 10:00AM |
V9.00010: Self-assembly of Nanoparticles into Planar Modulated Superstructures Michael Engel The advance in the synthesis of nanoparticles and colloids opens up the possibility to use them as building blocks for self-assembling novel materials. Ordered structures are especially interesting because they have unique photonic and electronic properties. Among the most complex ordered phases are commensurately and incommensurately modulated crystals. Although frequently found on the atomic scale in the bulk and as ordered structures of noble gases in adsorbed layers, modulated phases have so far not been known to self-assemble with nanoparticles. Here, we use computer simulations to study a two-dimensional system characterized by a simple isotropic interaction that could be realized in future with building blocks on the nanoscale. We find that the particles arrange themselves into planar hexagonal superstructures whose superlattice vector can be tuned reversibly by changing the temperature. Thermodynamic stability is confirmed by calculating the free energy with a combination of thermodynamic integration and the Frenkel-Ladd method. Different contributions to the free energy difference are discussed. [Preview Abstract] |
Thursday, March 24, 2011 10:00AM - 10:12AM |
V9.00011: Programmable, directed assembly of micron-scale components Caspar Floryan, Robert Westervelt Self assembly is a nascent paradigm for assembling components in the micron to millimeter size range. Such assemblies are often performed by modifying the surface chemistries of the individual components or by creating flow fields directing them into position. We propose a method of directed assembly using dielectric contrast between the components and a surrounding fluid. A hybrid integrated-circuit / microfluidic device\footnote{Thomas Hunt, David Issadore, Robert Westervelt ``Integrated Circuit/Microfluidic Chip to Programmably Trap and Move Cells and Droplets with Dielectrophoresis'' \textit{Lab on a Chip 8}, 81-87 (2008)} will be used to trap and manipulate pieces into pre-defined patterns. The device contains an array of electrically-chargeable pixels on its surface, with a resolution of 10 $\mu $m. [Preview Abstract] |
Thursday, March 24, 2011 10:12AM - 10:24AM |
V9.00012: Synthesis and Evaporative Self-Assembly of Polystyrene Nanotubes under Confinement Lu Zhang, Jodie Lutkenhaus Synthesis and manipulation of anisotropic building blocks into ordered structures has attracted increasing attention in recent years as nanowires and nanotubes (NWs/NTs) show great potential in many emerging technologies such as novel electric devices, optical units and biosensors. Here we use evaporation to align polystryrene NWs/NTs into distinct and interesting patterns. We synthesized polystyrene (PS) NWs/NTs of varied aspect ratio using anodic aluminum oxide (AAO) templates (200 nm pore size) using a melt-wetting technique. The template was removed, and NWs/NTs of controllable length ranging from several hundred nanometers to a few micrometers were released from the bulk PS film under ultrasonication. We further investigate the evaporative self-assembly of the synthesized polystyrene NTs under confined and ``open'' geometries and observe the alignment and assembled structures of the polystyrene NTs using scanning electron microscopy. Confocal laser scanning microscopy was also used to monitor the kinetics of the alignment process during evaporation. Results indicate that many factors (solvent, aspect ratio) contribute to the degree of NW/NT alignment relative to the evaporation front. [Preview Abstract] |
Thursday, March 24, 2011 10:24AM - 10:36AM |
V9.00013: Dynamic self-assembly of chemically-propelled nanoscale building blocks Yanping Chen, Yunfeng Shi Self-assembly technique offers spontaneous, massively-parallel structure formation from bottom-up. So far, most research efforts have been focused on static self-assembly that is thermally driven towards a thermodynamic equilibrium. Less attention has been paid to dynamic self-assembly that evolves to a non-equilibrium steady state under a dissipative driving force. This project aims to investigate the non-equilibrium self-assembly behaviors of chemically-propelled nanoscale building blocks via molecular dynamics simulations. We utilize a catalytic building block, that has been shown, when isolated, to exhibit self-motile behavior when immersed in a fuel environment. Upon increasing the number density of the building blocks, interesting collective behaviors emerge due to direct interactions between the building blocks or indirect interactions via the fuel environment. The simulation system is also subjected to an artificial operation of converting products back to fuel molecules. The heat generated by the exothermic chemical reaction will also be removed. In this way, a steady-state, as well as the resulting dynamic self-assembly pattern, can be obtained. [Preview Abstract] |
Thursday, March 24, 2011 10:36AM - 10:48AM |
V9.00014: Dynamic Self-Assembly and Self-Propulsion in Nonequilibrium Magnetic Colloidal Ensembles at a Liquid/Liquid Interface Alexey Snezhko, Igor Aranson Ensembles of interacting particles subject to external periodic energy fluxes often develop nontrivial dynamics. Magnetic colloidal particles suspended over an interface of two immiscible liquids and energized by vertical alternating magnetic fields give rise to novel dynamic self-assembled structures (``asters'') which are not accessible at the liquid/air interfaces. Ferromagnetically ordered nickel spherical particles have been used in our experiments. Novel structures are attributed to the interplay between surface waves, generated at the liquid/liquid interface by the collective response of magnetic microparticles to the alternating magnetic field, and hydrodynamic fields induced in the boundary layers of \textit{both} liquids forming the interface. Two types of magnetic order is reported. We show that self-assembled aster structures become distorted in the presence of a small in-plane dc magnetic field and develop self-propulsion. The speed of locomotion can be effectively tuned by the amplitude of the dc field. [Preview Abstract] |
Thursday, March 24, 2011 10:48AM - 11:00AM |
V9.00015: A Tunable Terahertz Detector Based On Self Assembled Plasmonic Structure on a GaAs 2DEG Che Jin Bae, Deepu George, Rohit Singh, Andrea Markelz Recently compact frequency sensitive THz detection has been achieved using gated gratings on 2DEG structure. The method is based on the resonant absorption of the 2D plasmon dependence on system dimension and the tunability of that dimension by depletion gating. Here we attempt to improve detector sensitivity, tunability and remove polarization dependence through the development of a gated grid design. The requirement for imaging applications of device dimensions on the order of $<$ 1 micron over a detector area of 4 mm2, suggest that standard lithographic approaches will be too costly for large scale detector production. Here we realize the gated grid plasmonic structure on 2DEG material by using nanosphere self assembly lithography. This fabrication method has not been widely developed for III-V processing but allows us to achieve large area sensitive detectors with tunability in the 1-4 THz range. In this paper we will discuss the fabrication method and characterization of the devices as a function of gate bias and temperature using FTIR and THz time domain measurements. [Preview Abstract] |
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