Study of C ₃H ₅ ⁺ ion deposition on polystyrene and polyethylene surfaces using molecular dynamics simulations

Molecular dynamics simulations of ion deposition processes are used to study the deposition of C ₃H ₅ ⁺ ions on crystalline polystyrene (PS) and polyethylene (PE) surfaces at energies of 50 and 25 eV. For each system, 80 trajectories are carried out on pristine surfaces and the incident angle in every case is normal to the surface. The forces are determined using the reactive empirical bond order method developed by Tersoff and parametrized for hydrocarbons by Brenner, coupled to long-range Lennard-Jones potentials. The simulations predict that the ions deposited at 50 eV either dissociate and stick to the surface or remain on the surface intact in 98% of the trajectories on PS, and in 89% of the trajectories on PE. At 25 eV, the ions are deposited intact in 70% of the trajectories on PS and dissociate in only 3%. No dissociation of the incident ions is predicted to occur on PE at 25 eV. Rather, the ions scatter away in 90% of the trajectories. Consequently, ion deposition on PE at 25 eV is predicted to be very inefficient for thin-film growth. Many more ions or major ion fragments (such as C ₂H _n and CH ₂) remain near the surface on PS than PE at 50 eV. Thus, in general, polyatomic ion deposition for thin film growth is more efficient on PS than PE, and deposition at 50 eV is more efficient than deposition at 25 eV.