S. Kodambaka

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

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Publications (91)505.5 Total impact

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    ABSTRACT: The design and synthesis of shape-directed nanoscale noble metal particles have attracted much attention due to their enhanced catalytic properties and the opportunities to study fundamental aspects of nanoscale systems. As such, numerous methods have been developed to synthesize crystals with tunable shapes, sizes, and facets by adding foreign species that promote or restrict growth on specific sites. Many hypotheses regarding how and why certain species direct growth have been put forward, however there has been no consensus on a unifying mechanism of nanocrystal growth. Herein, we develop and demonstrate the capabilities of a mathematical growth model for predicting metal nanoparticle shapes by studying a well known procedure that employs AgNO3 to produce {111} faceted Pt nanocrystals. The insight gained about the role of auxiliary species is then utilized to predict the shape of Pd nanocrystals and to corroborate other shape-directing syntheses reported in literature. The fundamental understanding obtained herein by combining modeling with experimentation is a step toward computationally guided syntheses and, in principle, applicable to predictive design of the growth of crystalline solids at all length scales (nano to bulk).
    Nanoscale 08/2014; · 6.73 Impact Factor
  • K W Schwarz, J Tersoff, S Kodambaka, F M Ross
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    ABSTRACT: Nanowire growth is generally considered a steady-state process, but oscillatory phenomena are known to often play a fundamental role. Here we identify a natural sequence of distinct growth modes, in two of which the catalyst droplet jumps periodically on and off a crystal facet. The oscillatory modes result from a mismatch between catalyst size and wire diameter; they enable growth of straight smooth-sided wires even when the droplet is too small to span the wire tip. Jumping-catalyst growth modes are seen both in computer simulations of vapor-liquid-solid growth, and in movies of Si nanowire growth obtained by in situ microscopy. Our simulations also provide new insight into nanowire kinking.
    Physical Review Letters 08/2014; 113(5):055501. · 7.73 Impact Factor
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    ABSTRACT: The motion of Au between AuSi liquid eutectic droplets, both before and during vapor-liquid-solid growth, is important in controlling tapering and diameter uniformity in Si nanowires. We measure the kinetics of coarsening of AuSi droplets on Si(001) and Si(111), quantifying the size evolution of droplets during annealing in ultra high vacuum using in situ transmission electron microscopy. For individual droplets, we show that coarsening kinetics are modified when disilane or oxygen is added: coarsening rates increase in the presence of disilane but decrease in oxygen. Matching droplet size measurements with coarsening models confirms that Au transport is driven by capillary forces, and that the kinetic coefficients depend on the gas environment present. We suggest that the gas effects are qualitatively similar whether transport is attachment limited or diffusion limited. These results provide insight into manipulating nanowire morphologies for advanced device fabrication.
    Nano letters. 07/2014;
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    ABSTRACT: In situ transmission electron microscopy observations of uniaxial compression of sub-300 nm diameter, cylindrical, single-crystalline 6H-SiC pillars oriented along 〈0001〉 and at 45° with respect to 〈0001〉 reveal that plastic slip occurs at room-temperature on the basal {0 0 0 1} planes at stresses above 7.8 GPa. Using a combination of aberration-corrected electron microscopy, molecular dynamics simulations and density functional theory calculations, we attribute the observed phenomenon to basal slip on the shuffle set along 〈11¯00〉. By comparing the experimentally measured yield stresses with the calculated values required for dislocation nucleation, we suggest that room-temperature plastic deformation in 6H-SiC crystals is controlled by glide rather than nucleation of dislocations.
    Acta Materialia. 01/2014; 80:400–406.
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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 density functional theory calculations with van der Waals corrections, we investigated how the interlayer orientation affects the structure and electronic properties of MoS2-graphene bilayer heterostructures. Changing the orientation of graphene with respect to MoS2 strongly influences the type and the value of the electronic bandgap in MoS2, while not significantly altering the binding energy between the layers or the interlayer spacing. We show that the physical origin of this tunable bandgap arises from variations in the S–S interplanar distance (MoS2 thickness) with the interlayer orientation, variations which are caused by electron transfer away from the Mo–S bonds.
    Applied Physics Letters 01/2014; 105(3):031603-031603-5. · 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. · 1.87 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. · 1.87 Impact Factor

Publication Stats

1k Citations
505.50 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