The experiments described here examine 25-100 eV CF 3 ϩ and C 3 F 5 ϩ ion modification of a polystyrene ͑PS͒ surface, as analyzed by x-ray photoelectron spectroscopy. The molecular dynamics computer simulations probe the structurally and chemically similar reactions of 20-100 eV CH 3 ϩ and C 3 H 5 ϩ with PS. CF 3 ϩ and C 3 F 5 ϩ each form a distribution of different fluorocarbon ͑FC͒ functional groups on PS in amounts dependent upon the incident ion energy, structure, and fluence. Both ions deposit mostly intact upon the surface at 25 eV, although they also undergo some crosslinking upon deposition. Fragmentation of the two ions increases as the ion energies are increased to 50 eV. Both ions show increases in total fluorine and fluorinated carbon content when changing the ion energy from 25 to 50 eV. The simulations predict that CH 3 ϩ and C 3 H 5 ϩ behave in a similar fashion to their FC analogs, remaining mostly intact and either embedding or scattering from the surface without reacting 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 of the collisions depend significantly on the structure of the incident isomer. The simulations further illustrate how the maximum penetration depth of ion fragments depends on ionic structure, incident energy, and the identity of the penetrating fragment. These ion-surface results are discussed in terms of their possible role in plasmas.

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In this paper we examine the mechanism of secondary ion yield enhancements previously observed for polyatomic projectiles by measuring the weight loss, volume loss, and surface composition of poly(methyl methacrylate) (PMMA) films sputtered by keV SF 5 + and Ar + projectile ions. The sputter yieldsthe amount of material removed from the surface by 3.0 keV SF 5 + projectilesswas found to be 2.2 ( 0.8 higher than for Ar + projectiles, measured by weight loss in the PMMA film with a quartz crystal microbalance. This result is consistent with sputter yield measurements reported here using 5.5 keV ions and stylus profilometry. Thus, the >10× enhancement in secondary ion yield in secondary ion mass spectrometry observed for polyatomic ion projectiles is not attributable to the modest ∼2× enhancements observed in the sputter yields for this molecular solid. Surface chemical measurements by X-ray photoelectron spectroscopy also indicated fundamental differences in atomic versus polyatomic sputtering mechanisms at 3.0 keV, but not at 0.7 keV. These results provide a reasonable explanation for the depth profiling capability demonstrated here on PMMA films for 5.5 keV SF 5 + ions that is not possible with isoenergetic Ar + ions. † Part of the special issue "John T. Yates, Jr. Festschrift".

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