Crystal order near the point of impact under static keV ion bombardment
Resource
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 152 (4): 449-458
Journal
Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms
Pages
449-458
Date Issued
1999
Date
1999
Author(s)
Abstract
The surface damage created by static bombardment of keV ions is investigated using the Ag surface as a model system. Results from molecular dynamics calculations show that the sputtering events induced by the static ion beam take place in the sub-ps time range. Studies on the property of the underlayer atoms which eject late in the collision cascade reveal that in this time range the lattice structure of the surface in the impact region is not severely disrupted by the impinging ion. The degree of the structural disturbance in the surface after atom sputtering is evaluated by calculating the average and the most probable distances of displacement of the residual atoms from their lattice sites. Most surface atoms in the impact region are displaced by only a fraction of the equilibrium bond length in the solid after the ion bombardment, although the distance of displacement may be larger than the Lindemann radius. The displacement does not increase monotonously with the size or the energy of the impinging ion. The dependence of the extent of surface damage upon the initial distance of the surface atom from the target atom is quantitatively determined. The extent of the structural destruction in the surface decreases rapidly with increasing initial distances of the surface atoms from the target atom. The surface order after the static ion bombardment is related to the density of the surface atoms exposed to the incident ions. The average distance of displacement calculated from the Ag{1 1 0} surface is about 0.2 lattice spacings smaller than those obtained from the Ag{1 0 0} and the Ag{1 1 1} surfaces. Applications of these results to the structural determination of surfaces using the static secondary ion mass spectrometry are discussed.
Type
journal article
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