Molecular Dynamics Simulations of Ion Beam Mixing
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MOLECULAR DYNAMICS SIMULATIONS OF ION BEAM MIXING
A.M. MAZZONE CNR - Istituto LAMEL - Via de' Castagnoli 1 - 40126 Bologna (Italy)
ABSTRACT
This work presents a molecular dynamics simulation of the intermixing of a metallic bilayer. The aim of the simulation is to elicit, in a more rigourous manner than in standard theoretical approaches, trends and phenomena taking place during the post-collisional stage of the cascade.
INTRODUCTION
Ion beam mixing has taken the position of a leading technique in the field of material preparation and many studies are being devoted to the characterization of the main physical mechanisms. In mixing the relative importance of purely collisional mixing, effects arising during the thermalization of the cascade and radiation enhanced diffusion are of the greatest importance. It is generally thought that the overwhelming majority of mixing takes place during the thermalization of the cascade and that at high temperature mixing is dominated by radiation enhanced diffusion [1, 2]. For the thermal spike behaviour of the cascade an atomistic modelling, based on molecular dynamics simulations (see for instance [3, 4]), has been developed only for one-component metallic targets and for primary energies of a few keV. In this work a molecular dynamics simulation method is used to describe intermixing of a metallic bilayer. The simulation conditions have been chosen to emphasize the low-energy (E < 50 eV) regime which is precursor of the increase of the lattice vibrational energy and of phenomena of heat transport. The purpose of the study is to elicit general trends and make qualitative comparisons with current concepts and with experiments. THE SIMULATION METHOD
The simulation cell represents a Fe/Ag bilayer and is formed by a bcc lattice on top of a fcc lattice. Each sublattice contains the same number of atoms (approximately 3000 atoms for each sublattice) and it has a cubic form (the two cubes superimposing) with a linear dimension of approximately 40 A. Various orientations of the two sublattices have been tested and the results reported in the following paragraph represent an average behaviour. The interface Fe/Ag is the geometrical termination of the atomic arrangements (no attempt has been made to model an interfacial potential barrier). It was found that the size of the simulation cell is sufficient to contain the dynamics of the effects described in the following paragraph and test calculations using sublattices with a linear dimension up to 80 A did not show any appreciable size-dependent effect acting Mat. Res. Soc. Symp. Proc. Vol. 223. 01991 Materials Research Society Downloaded from https://www.cambridge.org/core. UCSD University of California San Diego, on 12 Apr 2020 at 01:42:39, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-223-35
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on the mechanisms investigated in the present study. Prior to the irradiation the lattice is equilibrated at the preassigned temperature by using a constant temp
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