Molecular-dynamics simulations of nanoscale surface modification of Si(111) via local excitation

Abstract

Nanoscale surface modification on Si(111) caused by slow highly-charged ions is investigated using molecular-dynamics simulations. Following a recently proposed mechanism of this process, electrons within a localized region of the surface are excited to antibonding states during a short time interval, leading to structural instability. In the simulations this instability is studied by embedding a hemispherical region of 200-391 excited Si on a Si(111) surface. The excited-state bond breaking leads to a completely different dynamics and final result than Coulomb explosion. This is mainly due to a much lower pressure in the excited hemisphere, so very little modification is done to the surface outside the excited region. In many respects the results in this study agree with experiments better than Coulomb explosion, e.g., no shock waves are detected, fairly small sputtering yield, and the formation of surface roughness and amorphous structures. (c) 2000 The American Physical Society.