A beam scattering instrument for the dynamics studies of surface-induced dissociation processes

Abstract

A beam scattering instrument has been constructed to study the dynamics of ion-surface collisions, especially surface-induced dissociation of polyatomic ions. The instrument uses a bench top double focusing mass spectrometer as the source of a well-defined ion beam for transmission into a collision chamber. The primary ions are decelerated to desired ion energy (as low as 5 eV) by a series of tube lenses and collide the surface at 45°. Thus, the ion energy for surface-induced dissociations can be varied from ∼5 eV to ⩾1 keV. The secondary ions are energy and mass analyzed by a cylindrical energy analyzer and a quadrupole mass filter, respectively, and detected by a channel electron multiplier operating in pulse counting mode. The detector assembly can be rotated with respect to the collision center between the specular angle and surface parallel to measure intensity and energy distributions of scattered primary and fragment ions as a function of scattering angle. The newly constructed instrument has been tested for its performance and used to study the dissociation of ethanol molecular ions colliding with a self-assembled monolayer surface of fluorinated thiol on gold (111) crystal and first results are presented here.