Browsing by Author "Artyukhov, Vasilii I."

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    Breaking of Symmetry in Graphene Growth on Metal Substrates
    (American Physical Society, 2015) Artyukhov, Vasilii I.; Hao, Yufeng; Ruoff, Rodney S.; Yakobson, Boris I.
    In graphene growth, island symmetry can become lower than the intrinsic symmetries of both graphene and the substrate. First-principles calculations and Monte Carlo modeling explain the shapes observed in our experiments and earlier studies for various metal surface symmetries. For equilibrium shape, edge energy variations δE manifest in distorted hexagons with different ground-state edge structures. In growth or nucleation, energy variation enters exponentially as ∼eδE/kBT, strongly amplifying the symmetry breaking, up to completely changing the shapes to triangular, ribbonlike, or rhombic.
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    Equilibrium at the edge and atomistic mechanisms of graphene growth
    (National Academy of Sciences, 2012) Artyukhov, Vasilii I.; Liu, Yuanyue; Yakobson, Boris I.; Richard E. Smalley Institute for Nanoscale Science and Technology
    The morphology of graphene is crucial for its applications, yet an adequate theory of its growth is lacking: It is either simplified to a phenomenological-continuum level or is overly detailed in atomistic simulations, which are often intractable. Here we put forward a comprehensive picture dubbed nanoreactor, which draws from ideas of step-flow crystal growth augmented by detailed first-principles calculations. As the carbon atoms migrate fromthe feedstock to catalyst to final graphene lattice, they go through a sequence of states whose energy levels can be computed and arranged into a step-by-step map. Analysis begins with the structure and energies of arbitrary edges to yield equilibrium island shapes. Then, it elucidates how the atoms dock at the edges and how they avoid forming defects. The sequence of atomic row assembly determines the kinetic anisotropy of growth, and consequently, graphene island morphology, explaining a number of experimental facts and suggesting how the growth product can further be improved. Finally, this analysis adds a useful perspective on the synthesis of carbon nanotubes and its essential distinction from graphene.
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    A jellium model of a catalyst particle in carbon nanotube growth
    (AIP Publishing, 2017) Artyukhov, Vasilii I.; Liu, Mingjie; Penev, Evgeni S.; Yakobson, Boris I.
    We show how a jellium model can represent a catalyst particle within the density-functional theory based approaches to the growth mechanism of carbon nanotubes (CNTs). The advantage of jellium is an abridged, less computationally taxing description of the multi-atom metal particle, while at the same time in avoiding the uncertainty of selecting a particular atomic geometry of either a solid or ever-changing liquid catalyst particle. A careful choice of jellium sphere size and its electron density as a descriptive parameter allows one to calculate the CNT–metal interface energies close to explicit full atomistic models. Further, we show that using jellium permits computing and comparing the formation of topological defects (sole pentagons or heptagons, the culprits of growth termination) as well as pentagon–heptagon pairs 5|7 (known as chirality-switching dislocation).
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    New insights into the properties and interactions of carbon chains as revealed by HRTEM and DFT analysis
    (Elsevier, 2014) Casillas, Gilberto; Mayoral, Alvaro; Liu, Mingjie; Ponce, Arturo; Artyukhov, Vasilii I.; Yakobson, Boris I.; Jose-Yacaman, Miguel
    Atomic carbon chains have raised interest for their possible applications as graphene interconnectors as the thinnest nanowires; however, they are hard to synthesize and subsequently to study. We present here a reproducible method to synthesize carbon chains in situ TEM. Moreover, we present a direct observation of the bond length alternation in a pure carbon chain by aberration corrected TEM. Also, cross bonding between two carbon chains, 5ﾠnm long, is observed experimentally and confirmed by DFT calculations. Finally, while free standing carbon chains were observed to be straight due to tensile loading, a carbon chain inside the walls of a carbon nanotube showed high flexibility.