PNNL

Abstract

Collisions of Ar+ ions with three different surfaces (self assembled monolayer of fluorinated alkyl thiol, vapor deposited thin films of diamond and LiF) have been studied by mass and energy resolved ion-scattering spectrometry. Kinetic energy distributions of scattered ions measured as a function of ion’s initial kinetic energy and scattering angle show a single peak at the lowest energy (~25 eV) corresponding to the loss of a small amount (~6 – 9 eV) of kinetic energy by the Ar+ ions. However, as the collision energy is increased, two energetically and spatially distinct peaks are observed in the kinetic energy spectra. These two processes correspond to the low energy loss process as mentioned above and a very high energy loss process approaching close to the initial kinetic energy of the Ar+ ion. As the ion energy is increased further, the low energy process disappears and the total intensity of scattered ions decreases significantly. The low energy loss peak is interpreted as due to the interaction of the Ar+ ions with the self assembled monolayer surface acting as a bulk surface. All three surfaces behave in the same manner with only minor differences in the thresholds for the high energy loss process.