Effect of polyatomic ion structure on thin-film growth: Experiments and molecular dynamics simulations

The experiments described here examine 25-100 eV CF3+ and C3F5+ ion modific ation of a polystyrene (PS) surface, as analyzed by x-ray photoelectron spe ctroscopy. The molecular dynamics computer simulations probe the structural ly and chemically similar reactions of 20-100 eV CH3+ and C3H5+ with PS. CF 3+ and C3F5+ each form a distribution of different fluorocarbon (FC) functi onal groups on PS in amounts dependent upon the incident ion energy, struct ure, and fluence. Both ions deposit mostly intact upon the surface at 25 eV , although they also undergo some crosslinking upon deposition. Fragmentati on of the two ions increases as the ion energies are increased to 50 eV. Bo th ions show increases in total fluorine and fluorinated carbon content whe n changing the ion energy from 25 to 50 eV. The simulations predict that CH 3+ and C3H5+ behave in a similar fashion to their FC analogs, remaining mos tly intact and either embedding or scattering from the surface without reac ting at 20 eV. At 50 and 100 eV, the simulations predict fragmentation most or all of the time. The simulations also show that the chemical products o f the collisions depend significantly on the structure of the incident isom er. The simulations further illustrate how the maximum penetration depth of ion fragments depends on ionic structure, incident energy, and the identit y of the penetrating fragment. These ion-surface results are discussed in t erms of their possible role in plasmas. (C) 2000 American Institute of Phys ics. [S0021-8929(00)03122-4].