Atomic-Scale Quantification of the Chemical Modification of Polystyrene through S, SC, and SH Deposition from Molecular Dynamics Simulations
K Choudhary and LB Hill and C Glosser and TW Kemper and EW Bucholz and SB Sinnott, JOURNAL OF PHYSICAL CHEMISTRY C, 117, 12103-12110 (2013).
The chemical modification of amorphous polystyrene (PS) by the deposition of atomic S, SC, and SH with 25, 50, and 100 eV of incident kinetic energy is examined using classical molecular dynamics simulations. The forces are determined using the second-generation reactive empirical bond-order (REBO) potential that has been extended to include sulfur. In all cases, the S atoms or S-containing dimers are deposited randomly on the PS surface with a flux of about 0.4 x 10(24) ions/(cm(2) s), which is comparable to experimental values. The simulations predict the way in which the depth profiles vary as a function of the identity and kinetic energy of the incident atom or dimer. We also quantify the ways in which the surface is chemically modified and provide a profile of the chemical products formed on the surface, within the substrate, or in the material sputtered from the surface. The simulations predict that the maximum density of deposited atoms throughout the surface substrate, 3.32 X 10(18) / cm(3), occurs for S deposition with 50 eV of incident energy. We further predict that the highest molecular weight products are formed as a result of S deposition with 100 eV of energy. Additionally, the chemical reactions that occur during the deposition are found to depend on the beam energy for all the incident atoms or dimers considered. Negligible change in the surface roughness is predicted to occur as a result of these deposition processes.
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