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Title: Modified surface nanoscale explosion: Effects of initial condition and charge flow

Abstract

Molecular dynamics (MD) simulations have been performed to study surface nanoscale explosion due to slow highly charged ion (HCl)-surface interactions. In order to understand the interplay between the mechanisms for surface modification and the dynamical consequences of the explosion, a new simulation model 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 various rates 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 longer than the in-the-substrate neutralization time of the HCl (approximately 10 fs) deduced from experimental measurements. At the same time, positively charged surface ions are allowed to migrate away from the center region at an average speed of approximately 40 {angstrom} per picosecond. Compared to the results from pure Coulomb explosion in which charge exchange between surface atoms and surface ion is not allowed, the strength of the nano-explosion is not weakened but somewhat enhanced. When the time interval for ionization is reduced to instant charging but with other conditions unchanged,more » little influence on the formation of a crater was found between the two cases. The finite time interval for building up the charged region only postponed the formation of the repulsive center by approximately 25 fs and slightly lowered the peak value of the Coulomb repulsion. The explosion strength starts to decrease, however, as the speed of the charge flow in the substrate increases. In a test simulation, an estimation of a lower bound of surface damage as a function of surface energy deposition is provided by monitoring the dynamics according to the energetics of the systems. Dynamical consequences of these surface processes are studied by a comprehensive analysis of energetics, temperature, pressure, and structural information. The authors also discuss the relevance of the current model to HCI-surface experiments as well as to future modeling and simulations.« less

Authors:
;
Publication Date:
Research Org.:
Univ. of Florida, Gainesville, FL (US)
Sponsoring Org.:
USDOE
OSTI Identifier:
20075904
DOE Contract Number:  
FG02-97ER45660
Resource Type:
Journal Article
Journal Name:
Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical
Additional Journal Information:
Journal Volume: 104; Journal Issue: 19; Other Information: PBD: 18 May 2000; Journal ID: ISSN 1089-5647
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; MOLECULAR DYNAMICS METHOD; COULOMB FIELD; SPUTTERING; ION MICROPROBE ANALYSIS; MASS SPECTROSCOPY; CRATERS

Citation Formats

Hedstroem, M., and Cheng, H.P. Modified surface nanoscale explosion: Effects of initial condition and charge flow. United States: N. p., 2000. Web. doi:10.1021/jp993283u.
Hedstroem, M., & Cheng, H.P. Modified surface nanoscale explosion: Effects of initial condition and charge flow. United States. doi:10.1021/jp993283u.
Hedstroem, M., and Cheng, H.P. Thu . "Modified surface nanoscale explosion: Effects of initial condition and charge flow". United States. doi:10.1021/jp993283u.
@article{osti_20075904,
title = {Modified surface nanoscale explosion: Effects of initial condition and charge flow},
author = {Hedstroem, M. and Cheng, H.P.},
abstractNote = {Molecular dynamics (MD) simulations have been performed to study surface nanoscale explosion due to slow highly charged ion (HCl)-surface interactions. In order to understand the interplay between the mechanisms for surface modification and the dynamical consequences of the explosion, a new simulation model 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 various rates 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 longer than the in-the-substrate neutralization time of the HCl (approximately 10 fs) deduced from experimental measurements. At the same time, positively charged surface ions are allowed to migrate away from the center region at an average speed of approximately 40 {angstrom} per picosecond. Compared to the results from pure Coulomb explosion in which charge exchange between surface atoms and surface ion is not allowed, the strength of the nano-explosion is not weakened but somewhat enhanced. When the time interval for ionization is reduced to instant charging but with other conditions unchanged, little influence on the formation of a crater was found between the two cases. The finite time interval for building up the charged region only postponed the formation of the repulsive center by approximately 25 fs and slightly lowered the peak value of the Coulomb repulsion. The explosion strength starts to decrease, however, as the speed of the charge flow in the substrate increases. In a test simulation, an estimation of a lower bound of surface damage as a function of surface energy deposition is provided by monitoring the dynamics according to the energetics of the systems. Dynamical consequences of these surface processes are studied by a comprehensive analysis of energetics, temperature, pressure, and structural information. The authors also discuss the relevance of the current model to HCI-surface experiments as well as to future modeling and simulations.},
doi = {10.1021/jp993283u},
journal = {Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical},
issn = {1089-5647},
number = 19,
volume = 104,
place = {United States},
year = {2000},
month = {5}
}