Epitaxial Growth and Recovery: an Analytic Approach

1991 ◽  
Vol 237 ◽  
Author(s):  
A. Zangwillt ◽  
C. N. Luset ◽  
D. D. Vvedensky ◽  
M. R. Wilby
Keyword(s):  
Epitaxial Growth ◽  
Stochastic Equation ◽  
Morphological Evolution ◽  
Surface Profile ◽  
Equation Of Motion ◽  
Analytic Approach ◽  
Deposition Flux ◽  
Simulation Techniques ◽  
Continuum Equation ◽  
Computer Based

ABSTRACTMost detailed studies of morphological evolution during epitaxial growth and recovery make use of computer-based simulation techniques. In this paper, we discuss an alternative, analytic approach to this problem which takes explicit account of the atomistically random processes of deposition and surface diffusion. Beginning with a master equation representation of the dynamics of a solid-on-solid model of epitaxial growth, we derive a discrete, stochastic equation of motion for the surface profile. This Langevin equation is appropriate for growth studies. In particular, we are able to provide a microscopic justification for a non-linear continuum equation of motion proposed for this problem by others on the basis of heuristic arguments. During recovery, the deposition flux and its associated shot noise are absent. We analyze this process with a completely deterministic equation of motion obtained by performing a statistical average of the original stochastic equation. Results using the latter compare favorably with full Monte Carlo simulations of the original model for the case of the decay of sinusoidally modulated initial surfaces.

Instabilities, Elasticity, and Wetting Effect in Multilayer Heteroepitaxial Growth

2003 ◽  
Vol 794 ◽  
Author(s):  
Zhi-Feng Huang ◽  
Rashmi C. Desai
Keyword(s):  
Periodic Structures ◽  
Morphological Evolution ◽  
Surface Profile ◽  
Theoretical Work ◽  
Semiconductor Films ◽  
Morphological Instability ◽  
Heteroepitaxial Growth ◽  
Surface And Interface ◽  
Short Period ◽  
Short Period Superlattices

ABSTRACTFor multilayer semiconductor films comprising various material layers, the coupling of elastic states in different layers as well as the nonequilibrium nature of the growing process are essential in understanding the surface and interface morphological instability and hence the growth mechanisms of nanostructures in the overall film. We present the theoretical work on the stress-driven instabilities during the heteroepitaxial growth of multilayers, based on the elastic analysis and the continuous nonequilibrium model. We develop a general theory which determines the morphological evolution of surface profile of the multilayer system, and then apply the results to two types of periodic structures that are being actively investigated: alternating tensile/compressive and strained/spacer multilayers. The wetting effect, which arises from the material properties changing across layer-layer interfaces, is incorporated. It exhibits a significant influence of stabilization on film morphology, particularly for the short-period superlattices. Our results are consistent with the experimental observations in AlAs/InAs/InP(001) and Ge/Si(001) multilayer structures.

scholarly journals A Comprehensive Review of Cholinesterase Modeling and Simulation

Biomolecules ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 580
Author(s):  
Danna De Boer ◽  
Nguyet Nguyen ◽  
Jia Mao ◽  
Jessica Moore ◽  
Eric J. Sorin
Keyword(s):  
Modeling And Simulation ◽  
Binding Site ◽  
Catalytic Efficiency ◽  
Site Location ◽  
Simulation Techniques ◽  
Therapeutic Value ◽  
Docking Calculations ◽  
Computer Based ◽  
Dynamics Simulations ◽  
And Function

The present article reviews published efforts to study acetylcholinesterase and butyrylcholinesterase structure and function using computer-based modeling and simulation techniques. Structures and models of both enzymes from various organisms, including rays, mice, and humans, are discussed to highlight key structural similarities in the active site gorges of the two enzymes, such as flexibility, binding site location, and function, as well as differences, such as gorge volume and binding site residue composition. Catalytic studies are also described, with an emphasis on the mechanism of acetylcholine hydrolysis by each enzyme and novel mutants that increase catalytic efficiency. The inhibitory activities of myriad compounds have been computationally assessed, primarily through Monte Carlo-based docking calculations and molecular dynamics simulations. Pharmaceutical compounds examined herein include FDA-approved therapeutics and their derivatives, as well as several other prescription drug derivatives. Cholinesterase interactions with both narcotics and organophosphate compounds are discussed, with the latter focusing primarily on molecular recognition studies of potential therapeutic value and on improving our understanding of the reactivation of cholinesterases that are bound to toxins. This review also explores the inhibitory properties of several other organic and biological moieties, as well as advancements in virtual screening methodologies with respect to these enzymes.

Controlling Chaotic Vibrations of a Quarter-Car Model Excited by Road Surface Profile using Parametric Excitation.

2021 ◽  
Vol 6 (3) ◽  
Author(s):  
Lawrence Atepor ◽  
Keyword(s):  
Parametric Excitation ◽  
Surface Profile ◽  
Equation Of Motion ◽  
Road Surface ◽  
Force Term ◽  
Quarter Car Model ◽  
Car Model ◽  
Chaotic Vibrations ◽  
Excitation Force ◽  
Quarter Car

Chaotic Vibrations are considered for a quarter-car model excited by the road surface profile. The equation of motion is obtained in the form of a classical Duffing equation and it is modeled with deliberate introduction of parametric excitation force term to enable us manipulate the behavior of the system. The equation of motion is solved using the Method of Multiple Scales. The steady-state solutions with and without the parametric excitation force term is investigated using NDSolve MathematicaTM Code and the nonlinear dynamical system’s analysis is by a study of the Bifurcations that are observed from the analysis of the trajectories, and the calculation of the Lyapunov. In making the system more strongly nonlinear the excitation amplitude value is artificially increased to various multiples of the actual value. Results show that the system’s response can be extremely sensitive to changes in the amplitude and the that chaos is evident as the system is made more nonlinear and that with the introduction of parametric excitation force term the system’s motion becomes periodic resulting in the elimination of chaos and the reduction in amplitude of vibration.

scholarly journals Stochastic equation of motion approach to fermionic dissipative dynamics. II. Numerical implementation

2020 ◽  
Vol 152 (20) ◽  
pp. 204106 ◽  
Author(s):  
Arif Ullah ◽  
Lu Han ◽  
Yun-An Yan ◽  
Xiao Zheng ◽  
YiJing Yan ◽  
...  
Keyword(s):  
Stochastic Equation ◽  
Equation Of Motion ◽  
Numerical Implementation ◽  
Dissipative Dynamics

Scaling Description of Sub-Monolayer Epitaxial Growth

1992 ◽  
Vol 280 ◽  
Author(s):  
A. Zangwill
Keyword(s):  
Epitaxial Growth ◽  
Surface Diffusion ◽  
Diffusion Constant ◽  
Current Status ◽  
Future Research ◽  
Deposition Flux ◽  
Simple Relationship ◽  
Island Nucleation ◽  
Scanning Tunnelling ◽  
Tunnelling Microscopy

ABSTRACTRecent experimental results aimed at the measurement of surface diffusion constants by use of scanning tunnelling microscopy and diffraction techniques have reawakened interest in the statistical properties of two-dimensional island nucleation and growth in the submonolayer regime. Classical homogeneous rate equation studies published over twenty years ago established a simple relationship among the number density of stable islands, the deposition flux, and the adatom surface diffusion constant. Recent Monte Carlo simulation studies confirm this prediction and considerably extend the scope of such a scaling description of submonolayer epitaxial growth. In this article, I review the current status of theory and experiment in this area and suggest some areas for future research.

First-Principles Study of SI(lll) Homoepitaxy

1998 ◽  
Vol 538 ◽  
Author(s):  
Kyeongjae Cho ◽  
Efthimios Kaxiras
Keyword(s):  
Epitaxial Growth ◽  
First Principles ◽  
Morphological Evolution ◽  
Cluster Formation ◽  
Growth Conditions ◽  
Growth Modes ◽  
Pseudopotential Calculations ◽  
Step Density ◽  
Formation Energies ◽  
Microscopic Energy

AbstractEpitaxial growth on the Si(111) surface is studied using first-principles total-energy pseudopotential calculations. The energetics of added Si atoms essentially determines epitaxial growth modes under different growth conditions (surface temperature, Si flux rate, and surface step density). We have determined the surface adatom diffusion barriers and cluster formation energies; we use these microscopic energy parameters to address the possibilities for macroscopic morphological evolution of the surface under different conditions.

Morphology of Monolayer Films Observed by Photoelectron and Low-Energy-Electron Microscopy

1992 ◽  
Vol 280 ◽  
Author(s):  
M. Mundschau ◽  
E. Bauer ◽  
W. Świech
Keyword(s):  
Epitaxial Growth ◽  
High Temperatures ◽  
Deposition Flux ◽  
Atomic Step ◽  
High Flux ◽  
Monolayer Films ◽  
Atomic Steps ◽  
Molecular Beam Epitaxial ◽  
Adsorbed Atoms ◽  
Molecular Beam Epitaxial Growth

ABSTRACTMany of the fundamentals of epitaxial growth, long predicted by theories of crystal growth, have been seen during the molecular beam epitaxial growth of monolayer films. In general, high temperatures and low deposition flux favor nucleation at atomic steps. The opposite extreme of low temperature and high flux favors island nucleation in terraces, and steps play little role. For intermediate conditions a wide variety of growth morphology is seen. High temperatures and high flux have been seen to produce two-dimensional dendritic growth. Atomic steps on substrates have been observed to migrate during sublimation. Pinning of steps during migration gives rise to complex atomic step and terrace structures and a distribution of terrace widths. For terraces wider than the diffusion length of adsorbed atoms, nucleation of islands is favored in the terraces, whereas narrow terraces favor nucleation at the atomic steps. For a constant substrate temperature and deposition flux, morphology can vary profoundly depending upon local terrace width. Complex structures in monolayer films are produced during sublimation. These include lockeime or hole nuclei which are one atomic step deep. Steps are seen to oscillate during step flow apparently due to considerable mass transport between steps and terraces.

Calculated Surprises

2019 ◽  
Author(s):  
Johannes Lenhard
Keyword(s):  
Mathematical Modeling ◽  
Scientific Reasoning ◽  
Science And Technology ◽  
Human Capabilities ◽  
Epistemology Of Science ◽  
Simulation Techniques ◽  
Wide Range ◽  
Recent Developments ◽  
Computer Based ◽  
Key Features

In this book, Lenhard concentrates on the ways in which computers and simulation are transforming the established conception of mathematical modeling. His core thesis is that simulation modeling constitutes a new mode of mathematical modeling that is rearranging and inverting key features of the established conception. Although most of these new key features—such as experimentation, exploration, and epistemic opacity—have their precursors, the new ways in which they are being combined is generating a distinctive style of scientific reasoning. Lenhard also documents how simulation is affecting fundamental concepts of solution, understanding, and validation. He feeds these transformations back into the philosophy of science, thereby opening up new perspectives on longstanding oppositions. By combining historical investigations with practical aspects, the book is accessible for a broad audience of readers. Numerous case studies covering a wide range of simulation techniques are balanced with broad reflections on science and technology. Initially, what computers are good at is calculating—with a speed and accuracy far beyond human capabilities. Lenhard goes further and investigates the emerging characteristics of computer-based modeling, showing how this initially simple observation is creating a number of surprising challenges for the methodology and epistemology of science. These calculated surprises will attract both philosophers and scientific practitioners who are interested in reflecting on recent developments in science and technology.

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