The chemical modification of polystyrene surfaces by low-energy (10-100 eV) SF 5 + , C 3 F 5 + , and SO 3 + ions was studied by X-ray photoelectron spectroscopy and two-laser ion trap mass spectrometry. The mechanism of fluorination was found to be dissimilar for SF 5 + and C 3 F 5 + ions in this energy range at fluences of 10 14 -10 16 ions/cm 2 . SF 5 + was found to induce fluorination of the polymer surface by grafting reactive F atoms upon dissociation at impact. SF n fragments were not found to be grafted or implanted into the polymer. Sulfur was detected on the polymer surface only at incident energies above 50 eV and was found to be sulfidic in nature. In contrast, C 3 F 5 + ions induced grafting of both reactive F atoms and molecular C m F n fragments from the dissociation of the incident projectile. Larger proportions of highly fluorinated sites and thicker fluorocarbon layers were found for C 3 F 5 + at all energies and fluences. A variety of aliphatic and aromatic fluorine bonding environments were detected on both SF 5 + and C 3 F 5 + modified polystyrene surfaces.

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Fluorocarbon films were grown on polystyrene in vacuum from 25- to 100-eV mass-selected C3F5 + ion beams. The films were analyzed by X-ray photoelectron spectroscopy, atomic force microscopy, and X-ray reflectivity after exposure to the atmosphere for 4−8 weeks. The X-ray reflectivity indicates films that range from ∼30 to 60-Å thick. The thinner films form at lower ion energies, where the ion penetration depth and efficiency of film formation are lowest. X-ray reflectivity estimates air−fluorocarbon film roughness values of ∼6 Å for 25- and 50-eV films but ∼20 Å for the 100-eV films. The fluorocarbon−polystyrene-buried interface displays similar roughness and trends with ion energy. The AFM roughness trends are similar, but the absolute AFM roughnesses are only ∼/4 of the X-ray reflectivity values. This discrepancy is attributed to tip effects and the method of determining roughness by AFM. The AFM images and power spectral densities of the 100-eV films displayed quasi-periodic cones spaced 300−700 Å apart. Such features are either absent or of much lower amplitude in the 25- and 50-eV films. Classical molecular dynamics simulations of C3F5 + deposition on polystyrene at energies of 50 and 100 eV/ion reveal that etching at the higher energy is largely responsible for the dissimilar film structures obtained experimentally. These results demonstrate that deposition of the fluorocarbon polyatomic ion C3F5 + allows control of film nanostructure at the surface and buried interface.

We have improved our previously described method for extracting activation energies of fragmentation for polyatomic ions from surface-induced dissociation (SID) data [Wainhaus, S. B.; et al. J. Am. Chem. Soc. 1997, 119, 4001]. Our method analyzes the energy-resolved mass spectra and the kinetic energy distribution spectra of the parent and fragment ions that scatter off the surface. It extracts the activation energies by integrating over the distribution of the initial ion energy and the energy transferred to the surface, taking into account both the average value and the width of these distributions. The new method gave improved activation energies for SiMe3 + → SiMe x + (x = 0−2) fragmentation at a hexanethiolate-covered gold surface. We then used our data analysis method to analyze the activation energies for the fragmentation of thiophene ions at the hexanethiolate-covered gold surface. The activation energies for the formation of C2H2S+, CHS+, and C3H3 + from C4H4S+ were found to be 4.6 ± 0.7, 6.9 ± 0.7, and 6.5 ± 0.7 eV, respectively. Our activation energy results followed the trend in the values from threshold photoelectron photoion coincidence data. However, the SID values were ∼50% higher than the threshold photoelectron photoion coincidence values; this discrepancy mostly resulted from delayed dissociation. This model may be used to extract quantitative activation energies from SID data once certain ongoing issues are resolved in future papers. Molecular dynamics simulations were also performed to assist in the data analysis and to test the assumptions of energy transfer in this system. Qualitative agreement in energy transfer was found between the experiments and simulations.