Publications
240 results found
Dimastrodonato V, Pelucchi E, Vvedensky DD, 2013, Morphological evolution of seeded self-limiting quantum dots on patterned substrates, 31st International Conference on the Physics of Semiconductors (ICPS), Publisher: AMER INST PHYSICS, Pages: 31-+, ISSN: 0094-243X
Gocalinska A, Manganaro M, Pelucchi E, et al., 2012, Surface organization of homoepitaxial InP films grown by metalorganic vapor-phase epitaxy, PHYSICAL REVIEW B, Vol: 86, ISSN: 2469-9950
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- Citations: 21
Gill J, Vvedensky D, Salafia C, et al., 2012, CORRELATIONS BETWEEN INTRAVILLOUS SCREENING AND PLACENTAL FUNCTIONAL EFFICIENCY: THE INFLUENCE OF VILLOUS CAPILLARY GEOMETRY ONTO OXYGEN TRANSPORT FLUX, Meeting of the International-Federation-of-Placenta-Associations (IFPA), Publisher: W B SAUNDERS CO LTD, Pages: A18-A18, ISSN: 0143-4004
Dimastrodonato V, Pelucchi E, Vvedensky DD, 2012, Self-Limiting Evolution of Seeded Quantum Wires and Dots on Patterned Substrates, PHYSICAL REVIEW LETTERS, Vol: 108, ISSN: 0031-9007
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- Citations: 35
Lloyd-Williams JH, Monserrat B, Vvedensky DD, et al., 2012, Epitaxial kinetics with an intermediate polyatomic species, PHYSICAL REVIEW B, Vol: 85, ISSN: 2469-9950
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- Citations: 3
Seong R-K, Salafia CM, Vvedensky DD, 2012, Statistical topology of radial networks: a case study of tree leaves, PHILOSOPHICAL MAGAZINE, Vol: 92, Pages: 230-245, ISSN: 1478-6435
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- Citations: 2
Gill JS, Salafia CM, Grebenkov D, et al., 2011, Modeling oxygen transport in human placental terminal villi, JOURNAL OF THEORETICAL BIOLOGY, Vol: 291, Pages: 33-41, ISSN: 0022-5193
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- Citations: 43
Seong R-K, Salafia CM, Vvedensky DD, 2011, THE SHAPE OF THE CHORIONIC PLATE AND PLACENTAL VASCULATURE, Meeting of the International-Federation-of-Placenta-Associations (IFPA), Publisher: W B SAUNDERS CO LTD, Pages: A79-A79, ISSN: 0143-4004
Seong R-K, Salafia CM, Vvedensky DD, 2011, TREE TOPOLOGY OF PLACENTAL VASCULATURE, Meeting of the International-Federation-of-Placenta-Associations (IFPA), Publisher: W B SAUNDERS CO LTD, Pages: A78-A78, ISSN: 0143-4004
Pelucchi E, Dimastrodonato V, Rudra A, et al., 2011, Decomposition, diffusion, and growth rate anisotropies in self-limited profiles during metalorganic vapor-phase epitaxy of seeded nanostructures, Physical Review B, Vol: 83
We present a model for the interplay between the fundamental phenomena responsible for the formation of nanostructures by metalorganic vapor phase epitaxy on patterned (001)/(111)B GaAs substrates. Experiments have demonstrated that V-groove quantum wires and pyramidal quantum dots form as a consequence of a self-limiting profile that develops, respectively, at the bottom of V-grooves and inverted pyramids. Our model is based on a system of reaction-diffusion equations, one for each crystallographic facet that defines the pattern, and include the group III precursors, their decomposition and diffusion kinetics (for which we discuss the experimental evidence), and the subsequent diffusion and incorporation kinetics of the group-III atoms released by the precursors. This approach can be applied to any facet configuration, including pyramidal quantum dots, but we focus on the particular case of V-groove templates and offer an explanation for the self-limited profile and the Ga segregation observed in the V-groove. The explicit inclusion of the precursor decomposition kinetics and the diffusion of the atomic species revises and generalizes the earlier work of Biasiol et al. [Biasiol et al., Phys. Rev. Lett. 81, 2962 (1998); Phys. Rev. B 65, 205306 (2002)] and is shown to be essential for obtaining a complete description of self-limiting growth. The solution of the system of equations yields spatially resolved adatom concentrations, from which average facet growth rates are calculated. This provides the basis for determining the conditions that yield self-limiting growth. The foregoing scenario, previously used to account for the growth modes of vicinal GaAs(001) and the step-edge profiles on the ridges of vicinal surfaces patterned with V-grooves during metalorganic vapor-phase epitaxy, can be used to describe the morphological evolution of any template composed of distinct facets.
Farnudi B, Vvedensky DD, 2011, Large-scale simulations of ballistic deposition: The approach to asymptotic scaling, Physical Review E, Vol: 83
Farnudi B, Vvedensky DD, 2011, Large-scale simulations with distributed computing: Asymptotic scaling of ballistic deposition, Conference on Condensed Matter and Materials Physics (CMMP10), Publisher: IOP PUBLISHING LTD, ISSN: 1742-6588
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- Citations: 3
Zangwill A, Vvedensky DD, 2011, Novel growth mechanism of epitaxial graphene on metals, Nano Letters, Vol: 11, Pages: 2092-2095
Graphene, a hexagonal sheet of sp(2)-bonded carbon atoms, has extraordinary properties which hold immense promise for nanoelectronic applications. Unfortunately, the popular preparation methods of micromechanical cleavage and chemical exfoliation of graphite do not easily scale up for application purposes. Epitaxial graphene provides an attractive alternative, though there are many challenges, not least of which is the absence of any understanding of the complex atomistic assembly kinetics of graphene layers. Here, we present a simple rate theory of epitaxial graphene growth on close-packed metal surfaces. On the basis of recent low-energy electron-diffraction microscopy experiments, our theory supposes that graphene islands grow predominantly by the attachment of five-atom clusters. With optimized kinetic parameters, our theory produces a quantitative account of the measured time-dependent carbon adatom density. The temperature dependence of this density at the onset of nucleation leads us to predict that the smallest stable precursor to graphene growth is an immobile island composed of six five-atom clusters. This conclusion is supported by a recent study based on temperature-programmed growth of epitaxial graphene, which provides direct evidence of nanoclusters whose coarsening leads to the formation of graphene layers. Our findings should motivate additional high-resolution imaging experiments and more detailed simulations which will yield important input to developing strategies for the large-scale production of epitaxial graphene.
Farhadi AA, Vvedensky DD, 2010, Risk, randomness, crashes and quants, CONTEMPORARY PHYSICS, Vol: 44, Pages: 237-257, ISSN: 0010-7514
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- Citations: 2
Gill JS, Grebenkov DS, Salafia CM, et al., 2010, DIFFUSIVE OXYGEN FLUXES TO CAPILLARIES WITHIN THE HUMAN PLACENTA, International-Federation-of-Placental-Associations Meeting 2010, Publisher: W B SAUNDERS CO LTD, Pages: A41-A41, ISSN: 0143-4004
Seong R-K, Salafia CM, Vvedensky D, 2010, STATISTICAL TOPOLOGY OF PLACENTAL VASCULATURE, International-Federation-of-Placental-Associations Meeting 2010, Publisher: W B SAUNDERS CO LTD, Pages: A22-A22, ISSN: 0143-4004
Haselwandter CA, Vvedensky DD, 2010, Transient regimes and crossover for epitaxial surfaces, Physical Review E, Vol: 81
We apply a formalism for deriving stochastic continuum equations associated with lattice models to obtain equations governing the transient regimes of epitaxial growth for various experimental scenarios and growth conditions. The first step of our methodology is the systematic transformation of the lattice model into a regularized stochastic equation of motion that provides initial conditions for differential renormalization-group (RG) equations for the coefficients in the regularized equation. The solutions of the RG equations then yield trajectories that describe the original model from the transient regimes, which are of primary experimental interest, to the eventual crossover to the asymptotically stable fixed point. We first consider regimes defined by the relative magnitude of deposition noise and diffusion noise. If the diffusion noise dominates, then the early stages of growth are described by the Mullins-Herring (MH) equation with conservative noise. This is the classic regime of molecular-beam epitaxy. If the diffusion and deposition noise are of comparable magnitude, the transient equation is the MH equation with nonconservative noise. This behavior has been observed in a recent report on the growth of aluminum on silicone oil surfaces [Z.-N. Fang et al., Thin Solid Films 517, 3408 (2009)]. Finally, the regime where deposition noise dominates over diffusion noise has been observed in computer simulations, but does not appear to have any direct experimental relevance. For initial conditions that consist of a flat surface, the Villain-Lai-Das Sarma (VLDS) equation with nonconservative noise is not appropriate for any transient regime. If, however, the initial surface is corrugated, the relative magnitudes of terms can be altered to the point where the VLDS equation with conservative noise does indeed describe transient growth. This is consistent with the experimental analysis of growth on patterned surfaces [H.-C. Kan et al., Phys. Rev. Lett. 92, 146101 (20
Vvedensky DD, 2010, Quantum dots: Self-organized and self-limiting structures, Frontiers in Nanoscience and Nanotechnology, Editors: Narlikar, Fu, Oxford, Publisher: Oxford University Press, Pages: 205-233, ISBN: 9780199533046
Raymond L, Verga A, Vvedensky DD, 2009, Stochastic continuum model of submonolayer epitaxial growth, 7th Workshop on Epitaxial Semiconductor on Patterned Substrate and Novel Index Surfaces (ESPS-NIS), Publisher: ELSEVIER SCI LTD, Pages: 2-5, ISSN: 1369-8001
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- Citations: 1
Hasewandter CA, Vvedensky DD, 2008, Renormalization of atomistic growth models, INTERNATIONAL JOURNAL OF MODERN PHYSICS B, Vol: 22, Pages: 3721-3755, ISSN: 0217-9792
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- Citations: 7
Haselwandter CA, Raymond L, Verga A, et al., 2008, Occam's razor on surfaces: renormalization of microscopic processes, JOURNAL OF PHYSICS-CONDENSED MATTER, Vol: 20, ISSN: 0953-8984
Haselwandter CA, Vvedensky DD, 2008, Renormalization of stochastic lattice models: Epitaxial surfaces, Physical Review E, Vol: 77
We present the application of a method [C. A. Haselwandter and D. D. Vvedensky, Phys. Rev. E 76, 041115 (2007)] for deriving stochastic partial differential equations from atomistic processes to the morphological evolution of epitaxial surfaces driven by the deposition of new material. Although formally identical to the one-dimensional (1D) systems considered previously, our methodology presents substantial additional technical issues when applied to two-dimensional (2D) surfaces. Once these are addressed, subsequent coarse-graining is accomplished as before by calculating renormalization-group (RG) trajectories from initial conditions determined by the regularized atomistic models. Our applications are to the Edwards-Wilkinson (EW) model [S. F. Edwards and D. R. Wilkinson, Proc. R. Soc. London, Ser. A 381, 17 (1982)], the Wolf-Villain (WV) model [D. E. Wolf and J. Villain, Europhys. Lett. 13, 389 (1990)], and a model with concurrent random deposition and surface diffusion. With our rules for the EW model no appreciable crossover is obtained for either 1D or 2D substrates. For the 1D WV model, discussed previously, our analysis reproduces the crossover sequence known from kinetic Monte Carlo (KMC) simulations, but for the 2D WV model, we find a transition from smooth to unstable growth under repeated coarse-graining. Concurrent surface diffusion does not change this behavior, but can lead to extended transient regimes with kinetic roughening. This provides an explanation of recent experiments on Ge(001) with the intriguing conclusion that the same relaxation mechanism responsible for ordered structures during the early stages of growth also produces an instability at longer times that leads to epitaxial breakdown. The RG trajectories calculated for concurrent random deposition and surface diffusion reproduce the crossover sequences observed with KMC simulations for all values of the model parameters, and asymptotically always approach the fixed point corresponding t
Chua ALS, Pelucchi E, Rudra A, et al., 2008, Theory and experiment of step bunching on misoriented GaAs(001) during metalorganic vapor-phase epitaxy, Applied Physics Letters, Vol: 92
We present experiments and an accompanying theory for the growth modes during metalorganic vapor-phase epitaxy on vicinal GaAs(001). Our theory is based on a model that takes account of deposition, diffusion, and dissociation of molecular precursors, and the diffusion and step incorporation of atoms released by the precursors. The experimental conditions for island nucleation and growth, step flow, and step bunching are reproduced by this model, with the step bunching instability caused by the difference in molecular dissociation from above and below step edges.
Zangwill A, Vvedensky DD, 2007, Regimes of precursor-mediated epitaxial growth
A discussion of epitaxial growth is presented for those situations (OMVPE,CBE, ALE, MOMBE, GSMBE, etc.) when the kinetics of surface processes associatedwith molecular precursors may be rate limiting. Emphasis is placed on theidentification of various {\it characteristic length scales} associated withthe surface processes. Study of the relative magnitudes of these lengthspermits one to identify regimes of qualitatively different growth kinetics as afunction of temperature and deposition flux. The approach is illustrated with asimple model which takes account of deposition, diffusion, desorption,dissociation, and step incorporation of a single precursor species, as well asthe usual processes of atomic diffusion and step incorporation. Experimentalimplications are discussed in some detail.
Haselwandter CA, Vvedensky DD, 2007, Renormalization of stochastic lattice models: basic formulation., Phys Rev E Stat Nonlin Soft Matter Phys, Vol: 76, ISSN: 1539-3755
We describe a general method for the multiscale analysis of stochastic lattice models. Beginning with a lattice Langevin formulation of site fluctuations, we derive stochastic partial differential equations by regularizing the transition rules of the model. Subsequent coarse graining is accomplished by calculating renormalization-group (RG) trajectories from initial conditions determined by the regularized atomistic models. The RG trajectories correspond to hierarchies of continuum equations describing lattice models over expanding length and time scales. These continuum equations retain a quantitative connection over different scales, as well as to the underlying atomistic dynamics. This provides a systematic method for the derivation of continuum equations from the transition rules of lattice models for any length and time scales. As an illustration we consider the one-dimensional (1D) Wolf-Villain (WV) model [Europhys. Lett. 13, 389 (1990)]. The RG analysis of this model, which we develop in detail, is generic and can be applied to a wide range of conservative lattice models. The RG trajectory of the 1D WV model shows a complex crossover sequence of linear and nonlinear stochastic differential equations, which is in excellent agreement with kinetic Monte Carlo simulations of this model. We conclude by discussing possible applications of the multiscale method described here to other nonequilibrium systems.
Haselwandter CA, Vvedensky DD, 2007, Renormalization of stochastic lattice models: Basic formulation, PHYSICAL REVIEW E, Vol: 76, ISSN: 1539-3755
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- Citations: 26
Haselwandter CA, Vvedensky DD, 2007, Multiscale theory of fluctuating interfaces: Renormalization and self-organization, International Conference on Frontiers of Nonlinear and Complex Systems, Publisher: WORLD SCIENTIFIC PUBL CO PTE LTD, Pages: 4149-4155, ISSN: 0217-9792
Haselwandter CA, Vvedensky DD, 2007, Langevin equation for self-organized morphologies of thin heteroepitaxial films, International Conference on NANO-Structures Self Assembling, Publisher: ELSEVIER SCIENCE BV, Pages: 2762-2764, ISSN: 0039-6028
Haselwandter CA, Vvedensky DD, 2007, Multiscale theory of fluctuating interfaces: Renormalization of atomistic models, PHYSICAL REVIEW LETTERS, Vol: 98, ISSN: 0031-9007
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- Citations: 31
Haselwandter CA, Vvedensky DD, 2007, Fluctuation regimes of driven epitaxial surfaces, Europhysics Letters, Vol: 77
We derive the Langevin equation for the random deposition and diffusion of surface particles during homoepitaxial growth. The coefficients in this equation are determined directly by the growth parameters (temperature and flux) and provide initial conditions for renormalization-group transformations that reveal a hierarchy of continuum equations along the trajectory of coarse-grained length and time scales. Excellent agreement with previous kinetic Monte Carlo simulations of the atomistic model is obtained for all length and time scales and values of the growth parameters, but our analytic method also allows the systematic study of the interplay between deposition and diffusion for general experimental input parameters.
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