Low-Energy Ion−Surface Collisions Characterize Alkyl- and Fluoroalkyl-Terminated Self-Assembled Monolayers on Gold

Self-assembled monolayers (SAMs) formed from alkyl-terminated, CF 3 -terminated, CF 3 CF 2 -terminated, and C 10 F 21 -terminated alkanethiolates on gold substrates were examined by low-energy (eV) ion−surface collisions to determine the impact of varying the degree of fluorination of the thiolate tail group. The fluorine-terminated SAMs are compared and contrasted to previously examined CF 3 -terminated Langmuir−Blodgett films. Polyatomic (M + • for benzene and pyrazine) and atomic (Mo + • and Cr + • ) ions were collided with the different SAM films at various collision energies (20−70 eV). Data indicate that substitution of CH 3 with CF 3 as the terminal group has a substantial influence on the ion−surface interactions, including energy transfer (fragmentation), electron transfer (neutralization), and atom/group transfer (reaction). However, slight penetration into a depth of the film is apparent and illustrated with the formation of certain ion−surface reaction products and the intensities of those products. This penetration has a noticeable effect on low-energy ion−surface collisions. Also, results for a series of CF 3 (CH 2 ) n S−Au films (where n = 12, 13, 14, 15) illustrate that ion−surface reactions vary with the orientation of the fluorine atoms that are present in the terminal group. The results from collisions of low-energy ions with these relatively well-defined surfaces allow further characterization of the collision events that have the potential to become valuable tools in surface analysis.