142 research outputs found
Cluster-induced crater formation
Using molecular-dynamics simulation, we study the crater volumes induced by
energetic impacts ( km/s) of projectiles containing up to N=1000
atoms. We find that for Lennard-Jones bonded material the crater volume depends
solely on the total impact energy . Above a threshold \Eth, the volume
rises linearly with . Similar results are obtained for metallic materials.
By scaling the impact energy to the target cohesive energy , the crater
volumes become independent of the target material. To a first approximation,
the crater volume increases in proportion with the available scaled energy,
. The proportionality factor is termed the cratering efficiency and
assumes values of around 0.5.Comment: 9 page
Crater formation by fast ions: comparison of experiment with Molecular Dynamics simulations
An incident fast ion in the electronic stopping regime produces a track of
excitations which can lead to particle ejection and cratering. Molecular
Dynamics simulations of the evolution of the deposited energy were used to
study the resulting crater morphology as a function of the excitation density
in a cylindrical track for large angle of incidence with respect to the surface
normal. Surprisingly, the overall behavior is shown to be similar to that seen
in the experimental data for crater formation in polymers. However, the
simulations give greater insight into the cratering process. The threshold for
crater formation occurs when the excitation density approaches the cohesive
energy density, and a crater rim is formed at about six times that energy
density. The crater length scales roughly as the square root of the electronic
stopping power, and the crater width and depth seem to saturate for the largest
energy densities considered here. The number of ejected particles, the
sputtering yield, is shown to be much smaller than simple estimates based on
crater size unless the full crater morphology is considered. Therefore, crater
size can not easily be used to estimate the sputtering yield.Comment: LaTeX, 7 pages, 5 EPS figures. For related figures/movies, see:
http://dirac.ms.virginia.edu/~emb3t/craters/craters.html New version uploaded
5/16/01, with minor text changes + new figure
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