Probing surface properties with hyperthermal polyatomic ions:scattering of C_(60)~+ from highly oriented pyrolitic graphite,Au(111),and n-alkylthiol self-assembled monolayers

摘要

This influence of surface properties on the kinematice associated with hyperthermal grazing incidence scattering (E_(coII)=200-1000eV,#theta#_(in)=75deg)of large polyatomic ions was studied using the model projectile C_(60)~+.Surfaces cmployed were highly oriented pyrolitic graphite (HOPG),thin gold films on mica and self-assembled monolayers (SAMs)of n-lkylthiols on gold (of various chain lengths).Scattering kinematics was probed by measuring product angular and kinetic energy distributions.The internal energy distribution of scattered C_(60)~+ was determined with the help of unimolecular rate theory fits of resulting fragment mass spectra.HOPG and gold targets show qualitatively comparable scattering behavior,i.e.,both collision energy dependent subspecular scattering and partitioning of collision energy into possible degress of freedom are similar.SAMs,comprosed of molecules which may be deformed easily with respect to each other and to the surfsce,behave quite dirrerently.Specular scattering as well as uptake of a significantly larger amount of the incident kinetic energy (E_(coll))into the surface is observed-independent of chain length or chemical compositiion.Coupling of E_(coll) into scattered pojectile vibrations is found to be chain length dependent,with two classes of behavior observed.