Kinetic Monte Carlo Simulations of Strain-Induced Nanopatterning on Hexagonal Surfaces
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Kinetic Monte Carlo Simulations of Strain-Induced Nanopatterning on Hexagonal Surfaces M.I. Larsson1, B. Lee, R. Sabiryanov, K. Cho, W. Nix and B.M. Clemens Department of Material Science and Engineering, Stanford University, Stanford, CA 94305-2205, USA 1 on leave from Department of Physics, Karlstad University, Sweden ABSTRACT Guided self assembly of periodic arrays of quantum dots has recently emerged as an important research field not only to reduce component size and manufacturing cost but also to explore and apply quantum mechanical effects in novel nanodevices. The intention of this kinetic Monte Carlo (KMC) simulation study is to investigate self-organized nanopatterning on hexagonal surfaces for relaxed periodic surface strain fields applied to Pt(111) epitaxy. The KMC model is a full diffusion bond-counting model including nearest neighbor as well as second-nearest neighbor interactions with an event catalogue consisting of 8989 events modeling the effect of the biaxial surface strain field. The strain dependence of the fcc site and the saddle point for a Pt adatom migrating on top of the Pt(111) surface is calculated using the embedded atom method. Both the valley and the saddle point energies show an excellent linear dependence on the strain. These results are applied in the KMC model. The surface strain in this study is caused by a hexagonal network of dislocations at the interface between the substrate and a mismatched epitaxial layer. How the selforganization of deposited atoms is influenced by the surface strain will be addressed. INTRODUCTION Material science at the nanometer length scale is becoming more and more important mainly due to the miniaturization of electronic, magnetic and optical devices, but also because of the opportunity to experimentally investigate such quantum mechanical phenomena that could only be studied theoretically not very long ago. To understand the physical mechanism governing selforganization and nanopatterning, substantial theoretical [1] as well as experimental [2] efforts are necessary. One way to control the nanopatterning is to create a periodic strain field in the surface. This was experimentally demonstrated for growth of Fe and Ag on strained surfaces with periodic dislocation networks [3]. The dislocation networks were obtained by depositing 1-2 atomic mono layers (ML) of a mismatched material on the substrate at moderate temperature. The structure was thereafter annealed at a sufficiently high temperature to obtain strain relaxation by forming a network of dislocations. KMC simulations of the strain-induced effects on nucleation on a square lattice applying a sinusoidal biaxial strain field were reported by Mattsson and Metiu [4]. Another method to obtain periodic island arrays was described by Tersoff, Teichert and Lagally [5]. In this study the growth of a Si/Ge superlattice is modeled using continuum theory. At the interface between Si and Ge, the Ge forms islands due to the lattice mismatch. Thereafter, the Ge islands are buried in a Si matrix and the proce
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