S. Kodambaka

University of California, Los Angeles, Los Angeles, California, United States

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Publications (86)487.23 Total impact

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    ABSTRACT: Using in situ low-energy electron microscopy and density functional theory calculations, we follow the growth of monolayer graphene on Pd(111) via surface segregation of bulk-dissolved carbon. Upon lowering the substrate temperature, nucleation of graphene begins on graphene-free Pd surface and continues to occur during graphene growth. Measurements of graphene growth rates and Pd surface work functions establish that this continued nucleation is due to increasing C adatom concentration on the Pd surface with time. We attribute this anomalous phenomenon to a large barrier for attachment of C adatoms to graphene coupled with a strong binding of the non-graphitic C to the Pd surface.
    Applied Physics Letters 01/2014; 104(10):101606-101606-4. · 3.79 Impact Factor
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    ABSTRACT: Using in situ transmission electron microscopy, we investigated the kinetics of liquid Ga droplet decay on thin amorphous carbon films during annealing at 773 K. The transmission electron microscopy images reveal that liquid Ga forms spherical droplets and undergo coarsening/decay with increasing time. We find that the droplet volumes change non-linearly with time and the volume decay rates depend on their local environment. By comparing the late-stage decay behavior of the droplets with the classical mean-field theory model for Ostwald ripening, we determine that the decay of Ga droplets occurs in the surface diffusion limited regime.
    Applied Physics Letters 04/2013; 102(16). · 3.79 Impact Factor
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    ABSTRACT: We report a template-free, halide-free, efficient wet chemical method to synthesize defect-rich ZnO nanostructures with exposed {101} facets. The self-assembled ZnO nanostructures provide an active playground for catalytic reactions, such as CO2 hydrogenation, and exhibits great potential in alternative energy technologies.
    CrystEngComm 04/2013; 15(19):3780-3784. · 3.88 Impact Factor
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    ABSTRACT: An apparatus and test procedure for fabrication and loading of single crystal metal nanopillars under extremely high pressures (>1 GPa) and strain rates (>10(7) s(-1)), using laser-generated stress waves, are presented. Single-crystalline Cu pillars (∼1.20 μm in tall and ∼0.45 μm in diameter) prepared via focused ion beam milling of Cu(001) substrates are shock-loaded using this approach with the dilatational stress waves propagating along the [001] axis of the pillars. Transmission electron microscopy observations of shock-loaded pillars show that dislocation density decreases and that their orientation changes with increasing stress wave amplitude, indicative of dislocation motion. The shock-loaded pillars exhibit enhanced chemical reactivity when submerged in oil and isopropyl alcohol solutions, due likely to the exposure of clean surfaces via surface spallation and formation of surface steps and nanoscale facets through dislocation motion to the surface of the pillars, resulting in growth of thin oxide films on the surfaces of the pillars.
    Journal of Applied Physics 02/2013; 113(8):84309. · 2.21 Impact Factor
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    ABSTRACT: Pulsed laser operated high rate charging of Fe-doped LiNbO3 crystal for electron emission J. Appl. Phys. 112, 073107 (2012) Formation of nanostructured TiO2 by femtosecond laser irradiation of titanium in O2 J. Appl. Phys. 112, 063108 (2012) Finite element calculations of the time dependent thermal fluxes in the laser-heated diamond anvil cell An apparatus and test procedure for fabrication and loading of single crystal metal nanopillars under extremely high pressures (>1 GPa) and strain rates (>10 7 s À1), using laser-generated stress waves, are presented. Single-crystalline Cu pillars ($1.20 lm in tall and $0.45 lm in diameter) prepared via focused ion beam milling of Cu(001) substrates are shock-loaded using this approach with the dilatational stress waves propagating along the [001] axis of the pillars. Transmission electron microscopy observations of shock-loaded pillars show that dislocation density decreases and that their orientation changes with increasing stress wave amplitude, indicative of dislocation motion. The shock-loaded pillars exhibit enhanced chemical reactivity when submerged in oil and isopropyl alcohol solutions, due likely to the exposure of clean surfaces via surface spallation and formation of surface steps and nanoscale facets through dislocation motion to the surface of the pillars, resulting in growth of thin oxide films on the surfaces of the pillars. V C 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4793646]
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    ABSTRACT: By combining in situ and ex situ transmission electron microscopy measurements, we examine the factors that control the morphology of "hybrid" nanowires that include group III-V and group IV materials. We focus on one materials pair, GaP/Si, for which we use a wide range of growth parameters. We show through video imaging that nanowire morphology depends on growth conditions, but that a general pattern emerges where either single kinks or inclined defects form some distance after the heterointerface. We show that pure Si nanowires can be made to exhibit the same kinks and defects by changing their droplet volume. From this we derive a model where droplet geometry drives growth morphology and discuss optimization strategies. We finally discuss morphology control for material pairs where the second material kinks immediately at the heterointerface and show that an interlayer between segments can enable the growth of unkinked hybrid nanowires.
    Nano Letters 02/2013; · 13.03 Impact Factor
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    Surface and Coatings Technology 01/2013; 237:1. · 1.94 Impact Factor
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    ABSTRACT: Export Date: 26 January 2014, Source: Scopus, Art. No.: 121601
    Applied Physics Letters 01/2013; 103(12). · 3.79 Impact Factor
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    Thin Solid Films 01/2013; 549:1. · 1.60 Impact Factor
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    ABSTRACT: Using in situ high-temperature (700-1000 K) scanning tunneling microscopy (STM), we studied the influence of ethylene on the surface dynamics of oxygen-deficient, rutile-structured TiO2(110). STM images were acquired during annealing the sample as a function of time, oxygen and ethylene pressures, and temperature. With increasing oxygen pressure and/or decreasing temperature, TiO2(110) surface mass increased, consistent with previous results. Interestingly, annealing the sample in ethylene with traces of oxygen also results in the growth of TiO2 at higher rates than those observed during annealing in pure oxygen. Our results indicate that ethylene promotes oxidation of TiO2(110).
    Applied Physics Letters 11/2012; 101(21). · 3.79 Impact Factor
  • Suneel Kodambaka, Frances M. Ross
    10/2012;
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    ABSTRACT: The shape of nanocrystals determines surface atomic arrangement and coordination, influencing their chemical and physical properties. We present a novel and facile approach to synthesize gold icosahedra by employing glucose as reducing reagent and sodium dodecyl sulfate as directing agent in the environmentally benign medium of water at room temperature. The size of the icosahedra can be controlled in the range of 30–250 nm by altering reaction conditions. High‐resolution microscopy and diffraction studies indicate the icosahedra are composed of rotational twins that owe likely to assemblage of tetrahedral units. The gold icosahedra particles catalytic properties are probed in the borohydride reduction of p‐nitrophenols and exhibit a size‐dependence reaction property. Comparison studies with spherical particles prepared by the Turkevich method, coupled with poisoning experiments, infer that the shape has a strong influence in the abundance of active surface sites as well as their activities. The properties of nanoscale icosahedra particles has promising applications for further catalytic processes, surface enhancement spectroscopic methods, chemical or biological sensing, and the fabrication of nanoscale devices.
    ChemCatChem 10/2012; 4(10, October 2012). · 5.18 Impact Factor
  • Microscopy and Microanalysis 07/2012; 18(S2):1098-1099. · 2.50 Impact Factor
  • H. Ye, Z. Y. Yu, S. Kodambaka, V. B. Shenoy
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    ABSTRACT: The axial composition profiles in two-component alloy semiconductor nanowires are theoretically studied based on a comprehensive transient growth model which accounts for both surface diffusion and direct impingement of atoms to catalyst. The composition variation derives from the different growth rates contributed by each component. Our simulations reveal that the component with larger (smaller) diffusivity will segregate near the bottom (top) of the nanowire. In the presence (absence) of direct deposition on nanowire sidewalls, the steady state alloy composition is determined by the ratio of effective diffusion lengths (impingement rates to the catalyst).
    Applied Physics Letters 06/2012; 100(26). · 3.79 Impact Factor
  • Yuya Murata, V. Petrova, I. Petrov, S. Kodambaka
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    ABSTRACT: Using in situ high-temperature (1395 K), ultra-high vacuum, scanning tunneling microscopy (STM), we investigated the growth of bilayer graphene on 6H-SiC(0001). From the STM images, we measured areal coverages of SiC and graphene as a function of annealing time and found that graphene grows at the expense of SiC. Graphene domains were observed to grow, at comparable rates, at (I) graphene-free SiC step edges, (II) graphene–SiC interfaces, and (III) the existing graphene domain edges. Based upon our results, we suggest that the rate-limiting step controlling bilayer graphene growth is the desorption of Si from the substrate.
    Thin Solid Films 06/2012; 520(16):5289–5293. · 1.60 Impact Factor
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    ABSTRACT: Using in situ low-energy electron microscopy and density functional theory, we studied the growth structure and work function of bilayer graphene on Pd(111). Low-energy electron diffraction analysis established that the two graphene layers have multiple rotational orientations relative to each other and the substrate plane. We observed heterogeneous nucleation and simultaneous growth of multiple, faceted layers prior to the completion of second layer. We propose that the facetted shapes are due to the zigzag-terminated edges bounding graphene layers growing under the larger overlying layers. We also found that the work functions of bilayer graphene domains are higher than those of monolayer graphene, and depend sensitively on the orientations of both layers with respect to the substrate. Based on first-principles simulations, we attribute this behavior to oppositely oriented electrostatic dipoles at the graphene/Pd and graphene/graphene interfaces, whose strengths depend on the orientations of the two graphene layers.
    Physical Review B 05/2012; 85:205443. · 3.77 Impact Factor
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    ABSTRACT: In-situ high-temperature scanning tunneling microscopy was used to follow the coarsening (Ostwald ripening) and decay kinetics of single and multiple two-dimensional TiN islands on atomically flat TiN(001) terraces and in single-atom deep vacancy pits at temperatures of 750–950°C. The rate-limiting mechanism for island decay was found to be surface diffusion rather than adatom attachment/detachment at island edges. We have modeled island-decay kinetics based upon the Gibbs–Thomson and steady state diffusion equations to obtain a step-edge energy per unit length of 0.23±0.05 eV/Å and an activation energy for adatom formation and diffusion of 3.4±0.3 eV.
    Surface Review and Letters 04/2012; 07(05n06). · 0.28 Impact Factor
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    ABSTRACT: Using density functional theory calculations, we show that the binding strength of a graphene monolayer on Pd(111) can vary between physisorption and chemisorption depending on its orientation. By studying the interfacial charge transfer, we have identified a specific four-atom carbon cluster that is responsible for the local bonding of graphene to Pd(111). The areal density of such clusters varies with the in-plane orientation of graphene, causing the binding energy to change accordingly. Similar investigations can also apply to other metal substrates, and suggests that physical, chemical, and mechanical properties of graphene may be controlled by changing its orientation.
    Applied Physics Letters 01/2012; 102:051606. · 3.79 Impact Factor
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    ABSTRACT: Large-area graphene films are best synthesized via chemical vapour and/or solid deposition methods at elevated temperatures (~1,000 °C) on polycrystalline metal surfaces and later transferred onto other substrates for device applications. Here we report a new method for the synthesis of graphene films directly on SiO(2)/Si substrates, even plastics and glass at close to room temperature (25-160 °C). In contrast to other approaches, where graphene is deposited on top of a metal substrate, our method invokes diffusion of carbon through a diffusion couple made up of carbon-nickel/substrate to form graphene underneath the nickel film at the nickel-substrate interface. The resulting graphene layers exhibit tunable structural and optoelectronic properties by nickel grain boundary engineering and show micrometre-sized grains on SiO(2) surfaces and nanometre-sized grains on plastic and glass surfaces. The ability to synthesize graphene directly on non-conducting substrates at low temperatures opens up new possibilities for the fabrication of multiple nanoelectronic devices.
    Nature Communications 01/2012; 3:645. · 10.02 Impact Factor
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    ABSTRACT: Idealized nanowire geometries assume stable sidewalls at right angles to the growth front. Here we report growth simulations that include a mix of nonorthogonal facet orientations, as for Au-catalyzed Si. We compare these with in situ microscopy observations, finding striking correspondences. In both experiments and simulations, there are distinct growth modes that accommodate the lack of right angles in different ways--one through sawtooth-textured sidewalls, the other through a growth front at an angle to the growth axis. Small changes in conditions can reversibly switch the growth between modes. The fundamental differences between these modes have important implications for control of nanowire growth.
    Physical Review Letters 12/2011; 107(26):265502. · 7.94 Impact Factor

Publication Stats

1k Citations
487.23 Total Impact Points

Institutions

  • 2008–2014
    • University of California, Los Angeles
      • • Department of Materials Science and Engineering
      • • Department of Chemical and Biomolecular Engineering
      Los Angeles, California, United States
  • 2007–2013
    • Lund University
      • Division of Solid State Physics
      Lund, Skane, Sweden
  • 2001–2012
    • University of Illinois, Urbana-Champaign
      • Department of Materials Science and Engineering
      Urbana, Illinois, United States
  • 2008–2011
    • Purdue University
      West Lafayette, Indiana, United States
  • 2010
    • East China University of Science and Technology
      Shanghai, Shanghai Shi, China
  • 2006
    • IBM
      Armonk, New York, United States