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289 results on '"Vvedensky, Dimitri D."'

51. Pressure and flow statistics of Darcy flow from simulated annealing.

Author

Westbroek, Marise J E, King, Peter R, Vvedensky, Dimitri D, and Schwede, Ronnie

Subjects
SIMULATED annealing, SINGLE-phase flow, MULTIPHASE flow, DARCY'S law, THREE-dimensional flow, PATH integrals
Abstract

The pressure and flow statistics of Darcy flow through a three-dimensional random permeable medium are expressed as a path integral in a form suitable for evaluation by simulated annealing. There are several advantages to using simulated annealing for this problem: (i) any probability distribution can be used for the permeability, (ii) there is no need to invert the transmissibility matrix which, while not a factor for single-phase flow, offers distinct advantages for multiphase flow, and (iii) the action used for simulated annealing, whose extremum yields Darcy's law, is eminently suitable for coarse graining by integrating over the short-wavelength degrees of freedom. We show that the pressure and flow statistics obtained by simulated annealing are in excellent agreement with those obtained from standard finite-volume calculations. [ABSTRACT FROM AUTHOR]

Published
2021
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57. Growth kinetics and step density in reflection high-energy electron diffraction during molecular-beam epitaxy.

Author

Clarke, Shaun and Vvedensky, Dimitri D.

Subjects
*EPITAXY, *SURFACE chemistry, *CHEMICAL kinetics, *REFLECTION high energy electron diffraction
Abstract

Examines the kinetics of molecular-beam epitaxy by means of Monte Carlo simulations in combination with an approach for monitoring surface growth by calculating the evolution of the surface step density. Correspondence of the evolution of the step density to reflection high energy electron diffraction (RHEED) specular spot intensities for semiconductor compounds; Relation between RHEED measurements, kinetics and growth quality; Range of validity of the kinematic approach.

Published
1988
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60. Self-ordered nanostructures on patterned substrates.

Author

Pelucchi, Emanuele, Moroni, Stefano T., Dimastrodonato, Valeria, and Vvedensky, Dimitri D.

Subjects
BIOCHEMICAL substrates, NANOSTRUCTURES, EPITAXY, PHENOMENOLOGY, ANISOTROPY
Abstract

The formation of nanostructures during metalorganic vapor-phase epitaxy on patterned (001)/(111)B GaAs substrates is reviewed. The focus of this review is on the seminal experiments that revealed the key kinetic processes during nanostructure formation and the theory and modelling that explained the phenomenology in successively greater detail. Experiments have demonstrated that V-groove quantum wires and pyramidal quantum dots result from self-limiting concentration profiles that develop at the bottom of V-grooves and inverted pyramids, respectively. In the 1950s, long before the practical importance of patterned substrates became evident, the mechanisms of capillarity during the equilibration of non-planar surfaces were identified and characterized. This was followed, from the late 1980s, by the identification of growth rate anisotropies (i.e. differential growth rates of crystallographic facets) and precursor decomposition anisotropies, with parallel developments in the fabrication of V-groove quantum wires and pyramidal quantum dots. The modelling of these growth processes began at the scale of facets and culminated in systems of coupled reaction-diffusion equations, one for each crystallographic facet that defines the pattern, which takes account of the decomposition and surface diffusion kinetics of the group-III precursors and the subsequent surface diffusion and incorporation of the group-III atoms released by these precursors. Solutions of the equations with optimized parameters produced concentration profiles that provided a quantitative interpretation of the time-, temperature-, and alloy-concentration-dependence of the self-ordering process seen in experiments. [ABSTRACT FROM AUTHOR]

Published
2018
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62. Steering Epitaxial Growth

Author

Poelsema, Bene, van Dijken, Sebastiaan, Kotrla, Miroslav, Papanicolaou, Nicolas I., Vvedensky, Dimitri D., Wille, Luc T., and Physics of Interfaces and Nanomaterials

Subjects
METIS-211901, Magnetic anisotropy, Crystallography, Materials science, Condensed matter physics, Plane of incidence, Homogeneity (physics), Perpendicular, Polar, Surface finish, Thin film, London dispersion force
Abstract

Attractive dispersion forces, active between incident atoms and the substrate, cause preferential arrival of atoms on protruding parts on growing film surfaces. This phenomenon, which we refer to as “steering”, can give rise to significant flux redistribution. The lack of incident flux homogeneity, disregarded so far in growth studies, contributes to enhanced roughness of the growth front. This principal disadvantage can be turned around. In a quite narrow window of polar angles of incidence, it becomes possible to fabricate one-dimensional arrays of ripples oriented perpendicular to the plane of incidence. Several aspects of the mechanism, as well as an application of one-dimensional magnetic aggregates, are discussed.

Published
2002

63. Diffusion of Dimers on Silicon and Germanium (001) Surfaces

Author

Zandvliet, H.J.W., Zoethout, E., Poelsema, B., Kotrla, Miroslav, Papanicolaou, Nicolas I., Vvedensky, Dimitri D., Wille, Luc T., and Physics of Interfaces and Nanomaterials

Subjects
Condensed Matter::Quantum Gases, Substrate Atom, Materials science, Silicon, business.industry, Dimer, Stable Adsorption Site, chemistry.chemical_element, Germanium, Substrate (electronics), METIS-211900, chemistry.chemical_compound, Adsorption, Semiconductor, chemistry, Chemical physics, Physics::Atomic and Molecular Clusters, Direct consequence, Scanning Tunnelling Microscopy Image, Diffusion (business), business, Diffusion Pathway, Concerted Motion
Abstract

Atomic resolved imaging techniques have provided us with an exciting view on how atoms or clusters of atoms diffuse on surfaces. Here the stability and diffusion of Si and Ge dimers on elementary semiconductor (001) surfaces is briefly reviewed. It will be shown that, for these systems, in principle three diffusion pathways are active: diffusion of on-top dimers over the substrate rows, diffusion across the substrate rows, and diffusion in the troughs. Furthermore, we will report on a heretofore unknown phenomenon, namely, diffusion-driven concerted motion of substrate atoms. During diffusion of a dimer in the trough or across the substrate rows the substrate atoms in the proximity of the diffusing dimer exhibit a collective rearrangement. In retrospect, the occurrence of this concerted motion is not surprising at all, but is a direct consequence of the rearrangement of substrate atoms in the proximity of an adsorbed trough dimer.

Published
2002

83. Stochastic Equations for Thin Film Morphology.

Author

Yip, Sidney and Vvedensky, Dimitri D.

Abstract

Many physical phenomena can be modeled as particles on a lattice that interact according to a set of prescribed rules. Such systems are called "lattice gases". Examples include the non-equilibrium statistical mechanics of driven systems [1, 2], cellular automata [3, 4], and interface fluctuations of growing surfaces [5, 6]. The dynamics of lattice gases are generated by transition rates for site occupancies that are determined by the occupancies of neighboring sites at the preceding time step. This provides the basis for a multi-scale approach to non-equilibrium systems in that atomistic processes are expressed as transition rates in a master equation, while a partial differential equation, derived from this master equation, embodies the macroscopic evolution of the coarse-grained system. There are many advantages to a continuum representation of the dynamics of a lattice system: (i) the vast analytic methodology available for identifying asymptotic scaling regimes and performing stability analyses; (ii) extensive libraries of numerical methods for integrating deterministic and stochastic differential equations; (iii) the extraction of macroscopic properties by coarsegraining the microscopic equations of motion, which, in particular, enables (iv) the discrimination between inherently atomistic effects from those that find a natural expression in a coarse-grained framework; (v) the more readily discernible qualitative behavior of a lattice model from a continuum representation than from its transition rules, which (vi) helps to establish connections between different models and thereby facilitate the transferal of concepts and methods across disciplines; and (vii) the ability to examine the effect of apparently minor modifications to the transition rules on the coarse-grained evolution which, in turn, facilitates the systematic reduction of full models to their essential components. [ABSTRACT FROM AUTHOR]

Published
2005
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