Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session W12: Steps, Islands and Nanostructures |
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Sponsoring Units: DMP DCMP Chair: Ray Phaneuf, University of Maryland Room: 308 |
Thursday, March 19, 2009 11:15AM - 11:27AM |
W12.00001: Relaxation of Terrace-width Distributions: Novel Analysis and Features T.L. Einstein, Ajmi BH. Hamouda, A. Pimpinelli We describe a Fokker-Planck scheme to describe the relaxation of the terrace-width distribution (TWD) on a vicinal surface toward the generalized Wigner form describing equilibrium.\footnote{A.\ BH.\ Hamouda, A.\ Pimpinelli, \& TLE, Surface Sci. 602 (2008) 3569} We performed KMC calculations on the standard minimal SOS model to show that the time constant gives physical information, in particular the energy barrier of the rate-determining process. For close-packed steps, this involves kink-antikink generation, breaking 3 rather than the expected 2 lateral bonds (the latter associated with equilibrium fluctuations). We discuss strengths and limitations of this FP procedure, higher moments of the distribution beyond the variance, and generalizations to other step orientations. [Preview Abstract] |
Thursday, March 19, 2009 11:27AM - 11:39AM |
W12.00002: Narrowing of Terrace-width Distributions During Growth on Vicinals Ajmi BH. Hamouda, A. Pimpinelli, T.L. Einstein Using kinetic Monte Carlo simulations for a generic minimal SOS model of vicinal surfaces, we compute the terrace-width distributions (TWDs) as a function of incident flux during homoepitaxial growth. We show that the distribution narrows markedly,\footnote{ Ajmi BH. Hamouda, Ph.D. thesis, U.B.P.–Clermont 2} as though there were a flux-dependent repulsion between steps, until the step picture fails at high flux. Using a Fokker-Planck approach\footnote{A.\ BH.\ Hamouda, A. Pimpinelli, \& TLE, Surface Sci. 602 (2008) 3569 }, we analyze the evolution and saturation of this narrowing. We compare with a 1D model\footnote{H.-J. Gossman et al., J. Appl. Phys. 67 (1990) 745} and with our simulations for narrowing due to an Ehrlich-Schwoebel barrier. [Preview Abstract] |
Thursday, March 19, 2009 11:39AM - 11:51AM |
W12.00003: Stability and mobility of vacancy nanoclusters on Cu(111) surface: An {\it ab initio} study Alireza Akbarzadeh, Zhengzheng Chen, Nicholas Kioussis We used {\it ab initio} calculations to study stability and mobility of vacancy nanoclusters on Cu(111) surface. We found that the formation energies for single vacancies in the vicinity of surface are $\approx$0.3\,eV lower than that in bulk. Interestingly, calculations yield strongly bonded 1$^{st}$NN divacancy on the surface than in bulk. In addition a trivacancy binds very strong on the surface, indicating that formation of loop-like vacancy nanoclusters are most energetically favored on the surface. These findings imply the ease of nucleation of vacancy nanoclusters on the surface. We also examined migration of mono-, di- and trivacancy on the surface. A zigzag motion for divacancy diffusion on the surface is predicted with the migration barrier higher on the surface than in the bulk due to larger binding energy and elastic contribution. [Preview Abstract] |
Thursday, March 19, 2009 11:51AM - 12:03PM |
W12.00004: Two-dimensional island ripening on the basal plane of ice Shu Nie, Norm Bartelt, Konrad Thurmer Despite the importance of ice surfaces to many natural phenomena there have been no accurate measurements of \textit{surface} self-diffusion coefficients of ice. To provide this needed basic information, we applied the newly discovered capability of STM to image thick ice films on Pt [1], and tracked the evolution of 2-dimensional ice islands grown on the basal plane of ice. Uniform 5 nm thick ice films grown at 145 K were used as a template to study surface self-diffusion. By depositing a fraction of a monolayer of water onto these films at 115 K, we created arrays of two-dimensional islands with diameters of 5-10 nm. Remarkably, when annealed to temperatures between 115 and 135 K, these island arrays coarsened. By fitting the average island area to the t$^{2/3}$ growth law expected for diffusion-controlled ripening we extract an activation energy for surface self-diffusion of 0.4 $\pm $0.1 eV, which is on the order of the energy of a hydrogen bond and much less than the value measured for bulk diffusion (0.7 eV) [2]. This work is supported by U. S. DOE, OBES, Division of Materials Sciences under contract DE-AC04-94AL8500. [1] K. Th\"{u}rmer and N. C. Bartelt, Phys. Rev. B \textbf{77}, 195425 (2008). [2] D. E. Brown and S. M. George, J. Phys. Chem. \textbf{100}, 15460 (1996). [Preview Abstract] |
Thursday, March 19, 2009 12:03PM - 12:15PM |
W12.00005: Ferromagnetic-Semiconductor Interfacial Order Suppression: Self Assembled Fe$_{3}$Ga Island Structures on GaAs(001) Philip Ryan, Jong Woo Kim, Justin Shaw, Charles Falco, Lahsen Assoufid, Richard Rosenberg, David Keavney The practical development of spintronics requires a new class of multifunctional microelectronic components, involving electronic device mechanisms dependent upon ferromagnetic materials. The Fe-GaAs(001) system has been extensively studied as the prototypical spin injection junction for spintronic device mechanisms. Increasing spin injection efficiency has been calculated to be dependent upon the structural order of an abrupt interfacial junction between a ferromagnet and semiconductor. Room temperature low coverage Fe deposition on GaAs(001) reveals the formation of fully strained, epitaxial Fe$_{3}$Ga domains. An iron interfacial layer adheres fully coherent to the buried substrate surface. The adlayer is mediated through the back-bonding of the Fe to substrate terminating As. This structural environment is tied to the suppression of interfacial order. [Preview Abstract] |
Thursday, March 19, 2009 12:15PM - 12:27PM |
W12.00006: Snow flake shaped gold nanostructures templated on graphene: an avenue to fabricate novel nano electronic devices Kabeer Jasuja, Vikas Berry Non spherical gold nanoparticles such as rods, multipods, polygons, cubes, stars and branched nanostructures have generated significant research attention in the past few years. Such anisotropic nano structures have been shown to exhibit size and shape dependent properties which are either significantly different or highly pronounced from their spherical counterparts. The unique properties of anisotropic nanostructures (such as localized surface plasmon resonance and surface enhanced fluorescence) make these ideal candidates for a broad range of emerging applications in photonics, opto-electronics, biomedical labeling, sensing and imaging. One of the foremost challenges in utilizing such properties is integrating the anisotropic gold nanostructures into devices which can justifiably tap these properties. Here we demonstrate a simple colloidal synthetic route that results in the formation of snow-flake shaped nanostructures of gold (Au SFs) templated on the nano-sheets of Graphene-oxide(GO). Graphene nanosheets have generated renewed interest in recent years due to their unique 2-dimensional nature and associated electronic, physical and chemical properties. An assembly of Au SFs supported on GO sheets will not only give way to the next generation electronic and optoelectronic nanodevices but will also find wide ranging applications in a number of industrially relevant reactions such as catalysis, fuel cell technology and pollution control. [Preview Abstract] |
Thursday, March 19, 2009 12:27PM - 12:39PM |
W12.00007: Large-area nanocrystal superlattice films by surface-tension mediated self-assembly. Angang Dong, Christopher Murray We report a facile and general approach based on the dynamic self-assembly of nanocrystals on the liquid/liquid interface to fabricate hierarchically ordered nanocrystal superlattice films with areas up to several square centimeters. In addition to the close-packed ordering of nanocrystals at nanometer scale, the film exhibits exceptionally ordered stripe patterns at micrometer scale. The stripes are formed by the controlled, repetitive stick-slip motion of the liquid-liquid contact line. Both the film thickness and the stripe periodicity are tunable by changing the nanocrystal concentration. The final nanocrystal film, supported on the liquid surface, can be readily transferred to arbitrary substrates for device fabrication. The methodology reported here not only provides a simple and highly reproducible approach for production of large-area nanocrystal superlattice films, but also opens up a new avenue for lithography-free patterning of nanocrystal arrays for applications in optical, electronic, and magnetic devices. [Preview Abstract] |
Thursday, March 19, 2009 12:39PM - 12:51PM |
W12.00008: Mechanism of Asymmetric Growth of Wurtzite Nanostructures: A Case Study of CdSe Through Ab Initio Computations Ghanshyam Pilania, Ramamurthy Ramprasad An interesting and potentially useful phenomenon observed in wurtzite semiconductor nanocrystals is asymmetric anisotropic growth. This property has been exploited in the preferential creation of nanorods, nanoribbons and nanosaws over spherical nanocrystals. However, the details of the mechanism underlying this phenomenon of asymmetric anisotropic growth remain poorly understood. Here, we use CdSe as a prototypical wurtzite system, and oxygen as an agent that encourages asymmetric anisotropic growth. This study focus on the impact of the ordering of the surface energies of several polar and nonpolar surface facets as a function of (i) the chemical potential of Cd (i.e., precursor concentration), (ii) the presence of oxygen adsorbates, (iii) the binding modes of oxygen at the surface, and (iv) the density of oxygen adsorbates on the surfaces, using density functional theory (DFT). Our results show that by controlling the ordering of the surface energies (e.g., though proper choices of precursor concentration, temperature, and surfactants), novel growth modes such as asymmetric growth can be made possible. [Preview Abstract] |
Thursday, March 19, 2009 12:51PM - 1:03PM |
W12.00009: \textit{Ab Initio} Study of the Effects of Surface Chemistry and Size on Xray Absorption Spectra of CdSe Nanoparticles Heather Whitley, David Prendergast, Tadashi Ogitsu, Eric Schwegler The specificity of their opto-electronic properties with respect to size, shape, and surface chemistry, as well as cost-effective solution based methods of synthesis, make CdSe nanoparticles a material of choice for use in novel opto-electronic devices, such as photovoltaics and field effect transistors. Developing methods by which these nanomaterials can be systematically engineered to meet specific device goals is largely dependent on understanding how surface passivation and reconstruction affect the properties of a given nanomaterial. Xray absorption spectroscopy (XAS) is an ideal method for structural analysis, but its application to studying nanomaterial surfaces is nontrivial due to the convolution of the absorption of surface atoms with those within the nanomaterial. We utilize \textit{ab initio} methods to investigate the dependence of the Cd L-edge xray absorption cross-section on the size and passivation for Cd atoms both at the surface and within the core of CdSe nanomaterials. We aim to enable routine surface characterization of CdSe nanomaterials via XAS. Prepared by LLNL under Contract DE-AC52 07NA27344. [Preview Abstract] |
Thursday, March 19, 2009 1:03PM - 1:15PM |
W12.00010: Microwave induced in-situ deposition of Gold and Silver nanoparticles on chemically modified sheets of graphene: Avenue to build Graphene-metal interface Kabeer Jasuja, Vikas Berry In recent years there has been a great interest in the architecture of 2-D sheets of graphene which have been shown to display remarkable electronic, physical and chemical properties. An extremely high conductivity of graphene sheets along with the ease these can be prepared, has already made graphene as the material of choice for applications in several electronic, optoelectronic and biodevices. There is a great deal of interest in interfacing graphene sheets with other low dimensional nano structures for building novel hybrids. Coupling such low dimensional materials at nano scale yield novel composites with interesting properties. In this study we synthesized nanoparticles of gold and silver on the sheets of graphene-oxide using a one step microwave heating method. Our results indicate that the sheets of chemically modified graphene act as excellent templates for in-situ formation of gold and silver nanoparticles. The advantage of this present synthetic route lies in not using the conventional low molecular weight stabilizing agents which can otherwise react with the graphene sheets leading to impurities. This simple processing approach opens up a new way to synthesize hybrid sheets of graphene decorated with gold and silver nanoparticles which can be used in developing novel catalysts and composites. [Preview Abstract] |
Thursday, March 19, 2009 1:15PM - 1:27PM |
W12.00011: Efficient sticking of surface-passivated Si nanospheres via phase-transition plasticity Traian Dumitrica, Mayur Suri Large-scale atomistic simulations considering a $5$~nm in radius H-passivated Si nanosphere that impacts with relatively low energies onto a H-passivated Si substrate reveal a transition between two fundamental collision modes. At impacting speeds of less than $\sim1000$~m/s {\it particle-reflection} dominates. At increased speeds the partial onset in the nanosphere of a $\beta$-tin phase on the approach followed by $a$-Si phase on the recoil is an efficient dissipative route that promotes {\it particle-capture}. In spite of significant deformation, the integrity of the deposited nanosphere is retained. Our result explains the efficient fabrication of nanoparticulate films by hypersonic impaction, where the nanoparticle impact velocities equal $1000$--$2000$~m/s. \\[3pt] [1] M. Suri and T. Dumitric\u{a}, {\it Efficient Sticking of Surface-Passivated Si Nanospheres via Phase-Transition Plasticity}, Physical~Review~B [Rapid~Communication] {\bf 78}, 081405 (2008). \\[0pt] [2] P. Valentini and T. Dumitric\u{a}, {\it Microscopic Theory for Nanoparticle-Surface Collisions in Crystalline Silicon}, Physical Review B {\bf 75}, 224106 (2007). [Preview Abstract] |
Thursday, March 19, 2009 1:27PM - 1:39PM |
W12.00012: Electronic Nano-Structures as Ionic Barriers: A New Corrosion Prevention Concept Sreeya Sreevatsa, Haim Grebel Corrosion is a longstanding problem which costs the economy billions of dollars annually. The simplest way to prevent corrosion is to use paint thereby blocking diffusion of corrosive component towards the metallic surface. Here we consider a new concept - the electronic barrier -- for corrosion prevention. The barrier is an electronic p-n junction made by topping one film of functionalized carbon nanotubes on another. The barrier is constructed such that the positive ions in the electrolyte are prohibited from reaching the metallic surface through electronic screening. Potentiodynamic tests, Raman spectroscopy and inspection by scanning electron microscope revealed that the order of the layers (namely, p-n or n-p with respect to the metal surface does determine whether the metal corrodes or not. Numerical analysis of the structure will be provided as well. [Preview Abstract] |
Thursday, March 19, 2009 1:39PM - 1:51PM |
W12.00013: Ion-beam-assisted nano-texturing of halite-structure thin films Vladimir Matias We study biaxial crystalline texturing at early film growth in a variety of compounds during ion-beam-assisted deposition (IBAD). We have found that many different halite-structure compounds share the ion-beam texturing ability at nucleation and early film growth. This includes numerous oxides and nitrides. Fluorite-structure compounds also exhibit the possibility of fast IBAD texturing. For these materials IBAD texturing can be achieved within the first few nanometers of deposited material. We examine the detailed texture evolution for MgO. To perform these experiments we developed a unique experimental methodology based on linear combinatorial research. Three different texture development regions can be identified in MgO texture evolution. The first stage where biaxial texture first appears is during grain nucleation. There is evidence of a phase transition in this region. With additional IBAD texture continues to improve by grain alignment up to a certain point. Further improvement in crystalline alignment can be achieved by a third stage of epitaxial overgrowth. We find that the IBAD texture development is very sensitive to the nucleation surface conditions, both chemical species and surface morphology. An in-plane texture of less than 2\r{ } and an out-of-plane texture of less than 1\r{ } are attainable in an artificially textured MgO layer on an amorphous substrate This work is supported by the DOE Office of Electricity Delivery {\&} Energy Reliability. [Preview Abstract] |
Thursday, March 19, 2009 1:51PM - 2:03PM |
W12.00014: Intercalant Based E-Beam Lithography on a Layered Dichalcogenide Surface Timothy Kidd, Tyler Rash, Laura Strauss We have developed a novel method for creating surface structures on the surface of dichalchogenides using a scanning electron microscope. Using a single shot chemical vapor transport method, large (several mm diameter) single crystals of TiSe2 were synthesized with thin films of CuI upon their surfaces. The films were locally ordered, with distinct pyramidal nanostructures detected using atomic force microscopy (AFM) and scanning electron microscopy (SEM). After removing the surface layers via cleaving, the CuI films at the surface could be renewed by heating the sample. However, it was also found that the formation of these secondary CuI films could be impeded locally by controlled scanning of the SEM. In this way, one could create artificial micro- or nano- structured films upon the dichalcogenide surface in a manner similar to that of standard E-beam lithography. This technique could be used in the development of unique electro-optical devices on dichalchogenide crystal or thin film substrates. [Preview Abstract] |
Thursday, March 19, 2009 2:03PM - 2:15PM |
W12.00015: Mesoscopic Modeling of Nanostructured Strained Films: Single-Component vs. Alloy Systems Zhi-Feng Huang, Ken Elder The instability and nanostructure formation in strained solid films are examined through a mesoscopic approach that we developed recently to incorporate both the film crystalline structure and standard continuum theory. It is based on the phase field crystal (PFC) model and particularly the corresponding amplitude equation analysis of the slowly varying film surface profile, for both single-component and binary alloy films. A universal scaling relation for strained island size is identified, showing a crossover from the continuum elasticity result at the weak strain limit to a behavior governed by the ``perfect'' lattice relaxation condition [1]. We also analyze the coupling between the film composition distribution and the evolution of film morphology and nanostructures in alloy systems. Our results indicate the breakdown of conventional continuum approaches even at relatively large scales due to the discrete nature of the film crystalline structure. \\[3pt] [1] Z.-F. Huang and K. R. Elder, Phys. Rev. Lett. 101, 158701 (2008). [Preview Abstract] |
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