Chemical Modification of Polystyrene Surfaces by Low-Energy Polyatomic Ion Beams

Abstract

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.

Molecular Dynamics Simulations of the Chemical Modification of Polystyrene through CxFy+Beam Deposition

“…Surface etching yields are approximately the same for the two ions at 0.26 C atom/ion and 0.29 H atom/ion for C 3 F 5 + and 0.28 C atom/ion and 0.31 H atom/ion for CF 3 + . However, total F uptake and deposition yield are higher for CF 3 + than for C 3 higher velocity of the CF 3 + . However, the highest density of F occurs at a depth of 10-15 Å for both C 3 F 5 + and CF 3 + ion beams.…”

“…Specifically, the average penetration depths are 16.0 Å for both C and F atoms after C 3 F 5 + ion deposition and 15.9 and 15.2 Å for C and F, respectively, in the case of CF 3 + ion deposition. More F atoms chemically bond to the PS during CF 3 + ion deposition than during C 3 F 5 + ion deposition, as shown in Tables 3 and 4. In general, ions or ion fragments that form covalent bonds with the polymer substrate have smaller penetration depths than nonbonded, embedded species.…”

“…The polymer backbone structures are randomized; consequently, their volume increases by ion bombardment. Because of the higher incident ion velocities and consequently larger transfer of energy to the surface, CF 3 + ion deposition induces more disordering and swelling of the PS than C 3 F 5 + ion deposition. Surface etching yields are approximately the same for the two ions at 0.26 C atom/ion and 0.29 H atom/ion for C 3 F 5 + and 0.28 C atom/ion and 0.31 H atom/ion for CF 3 + .…”

“…Because of the higher incident ion velocities and consequently larger transfer of energy to the surface, CF 3 + ion deposition induces more disordering and swelling of the PS than C 3 F 5 + ion deposition. Surface etching yields are approximately the same for the two ions at 0.26 C atom/ion and 0.29 H atom/ion for C 3 F 5 + and 0.28 C atom/ion and 0.31 H atom/ion for CF 3 + . However, total F uptake and deposition yield are higher for CF 3 + than for C 3 higher velocity of the CF 3 + .…”

On the importance of ions and ion-molecule reactions to plasma-surface interface reactions

“…Although early workers in the field of plasma polymerization identified ions as important film precursors [6], radical species are most often cited as polymerization building blocks. Recently, Hanley and coworker have shown that ion beams of hyperthermal ions can produce thin films and can be used to modify material interfaces [7,8,9]. The size and structure of the ions used (i.e., CF 3 ϩ vs. C 3 F 5 ϩ ) can strongly affect film composition, structure, and surface reactivity of the ion.…”