| Abstract
| - Molecular dynamics (MD) simulations have been performed to study surface nanoscale explosion due toslow highly charged ion (HCI)−surface interactions. In order to understand the interplay between themechanisms for surface modification and the dynamical consequences of the explosion, a new simulationmodel is formulated to include the electronic degrees of freedom in an empirical manner. In this model,surface ionization occurs at a finite rate and surface charges are allowed to flow into the substrate at variousrates simultaneously. In one of the simulations based on the simultaneous ionization and charge migration(SICM) model, 100 excitations (positively charged surface ions) occur during the first 24 fs, which is longerthan the in-the-substrate neutralization time of the HCI (approximately 10 fs) deduced from experimentalmeasurements. At the same time, positively charged surface ions are allowed to migrate away from the centerregion at an average speed of approximately 40 Å per picosecond. Compared to the results from pure Coulombexplosion in which charge exchange between surface atoms and surface ion is not allowed, the strength ofthe nano-explosion is not weakened but somewhat enhanced. When the time interval for ionization is reducedto instant charging but with other conditions unchanged, little influence on the formation of a crater wasfound between the two cases. The finite time interval for building up the charged region only postponed theformation of the repulsive center by approximately 25 fs and slightly lowered the peak value of the Coulombrepulsion. The explosion strength starts to decrease, however, as the speed of the charge flow in the substrateincreases. In a test simulation, an estimation of a lower bound of surface damage as a function of surfaceenergy deposition is provided by monitoring the dynamics according to the energetics of the systems. Dynamicalconsequences of these surface processes are studied by a comprehensive analysis of energetics, temperature,pressure, and structural information. We also discuss the relevance of the current model to HCI−surfaceexperiments as well as to future modeling and simulations.
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