Computational investigation of the chemical modification of polystyrene through fluorocarbon and hydrocarbon ion beam deposition

Classical molecular dynamics (MD) simulations are used to study the effect of continuous hydrocarbon (HC) and fluorocarbon (FC) ion beam deposition on a polystyrene (PS) surface. Plasma processing is widely used to chemically modify surfaces and deposit thin films, and it is well-accepted that polyatomic ions and neutrals within low-energy plasmas have a significant effect on the surface chemistry. Here a comparison is made of the manner in which polyatomic FC ions and similarly structured HC ions react with PS and produce new structures. Specifically, the deposition of beams of C ₃H ₅ ⁺, CH ₃ ⁺, C ₃F ₅ ⁺, and CF ₃ ⁺ on PS surfaces at experimental fluences is considered. The simulations predict that the backbone chains are modified significantly more than the phenyl groups and that larger ions with lower velocities and larger collision cross sections modify the substrate to a shallower depth than smaller ions with higher velocities, even though all their incident kinetic energies are the same. Additionally, HC ions dissociate more readily than FC ions during deposition. Consequently, smaller HC ions are predicted to chemically modify the polystyrene to a greater extent than larger HC ions or FC ions.