Evidence for the bulk nature of self-assembled monolayer surface of fluorinated alkyl thiol from hyperthermal energy ion-surface collisions

Kinetic energy distributions of fragment ions from hyperthermal energy collisions of CF3+ ions with a self-assembled monolayer surface of fluorinated alkyl thiol on gold substrate and a LiF surface (vapor deposited on titanium substrate) have been measured as a function of scattering angle and fragment ion mass. These distributions for the thiol surface show two energetically and angularly distinct pathways for the dissociation of CF3+ ions while those from LiF show only one peak. A plot of the velocities of the fragment ions as a Newton diagram for these two processes clearly demonstrates that one process is due to the collision of ions with a fraction of the molecular chain of the monolayer surface molecule with scattering over a broader angular range while the other process is due to collision of the projectile ions with the monolayer surface acting as a bulk surface with fragment ions scattering close to the surface parallel and resembles the Newton diagram from the LiF surface.