Chemical modification of fluorinated self-assembled monolayer surfaces using low-energy ion beams for halogen and pseudohalogen transfer

Isocyanatosilane-derived cations, Si(NCO)n +, (n=1–4) were mass-selected and reacted with fluorinated self-assembled monolayer (F-SAM) surfaces at low collision energy (<100 eV). Examination of the scattered products revealed a variety of reactions from simple fluorine atom abstraction (e.g. formation of SiF+ ) to halogen–pseudohalogen exchange products (e.g. formation of SiF(NCO)2+ and SiF2(NCO)+ from Si(NCO)3+). Bare Si +• reacts predominantly by single F-atom abstraction, but small amounts of SiF2 +• and SiF3+ were also observed. The correlation of reactivity with thermochemistry and the role of the electronic configuration of projectile ions in multiple F-atom abstraction processes are discussed. Chemical modification of the F-SAM surface itself was shown to be a consequence of the ion–surface collisions. For example, in situ Xe+• chemical sputtering analysis of F-SAM surfaces exposed to Si(NCO)n+ ion beam bombardment revealed the presence of CF2NCO+ (m/z 92). This result suggests that NCO groups are incorporated into the fluorocarbon chains at the surface, probably via a pseudohalogen-by-halogen exchange mechanism. Surface modification was also achieved using the dicyanatochloromethyl cation, C(CN)2Cl +. Prolonged reactive collisions of C(CN) 2Cl+ upon a F-SAM surface led to the incorporation of both chlorine atom and cyanato groups into the surface, and these were released as CF2CN+ (m/z 76) and CF2Cl+ (m/z 85) on Xe+ • sputtering analysis. Isotopic labeling experiments confirmed Cl substitution into the surface fluorocarbon chains.