COLLISIONS OF FLUOROCARBON IONS AT SOLID-SURFACES - ELECTRONIC EXCITATION, SURFACE-INDUCED DISSOCIATION AND CHEMICAL SPUTTERING

Collisions of C3F6+. at self-assembled hydrocarbon, deuterated hydroca rbon and fluorocarbon surfaces yield fragment ions which are character istic of both electronic excitation and vibrational excitation. Direct electronic excitation is indicated by loss of F., which has been show n previously to be diagnostic of this type of excitation process. Elec tronic excitation is favored by low-energy collisions at the hydrocarb on surface. Even the change to the corresponding deuterated surface pr oduces a large effect in favor of the normal vibrational excitation pr ocess. This change in mechanism with the nature of the target shows up as a dramatic isotope effect in the surface-induced dissociation (SID ) mass spectra. The control over the excitation process exhibited by t he effective mass of the target is probably exerted through its effect on the relative velocity of the collision partners. The fluorinated s urface is more effective than the others in conversion of translationa l into internal energy and in minimizing ion loss through neutralizati on and other processes which compete with SID. The fluorinated surface s yield spectra that are largely free from chemical sputtering, a proc ess which occurs even at ultra-high vacuum for stainless-steel surface s which are not rigorously cleaned. The internal energy deposition ass ociated with chemical sputtering increases with increasing collision e nergy. Several of the fluorocarbon fragment ions generated from perflu oropropylene have also been examined at self-assembled monolayer surfa ces and they are well behaved in their SID and chemical sputtering rea ctions. This in contrast to the low efficiency of SID and high sputter ing efficiency observed in previous studies at uncharacterized multi-l ayer hydrocarbon-covered surfaces.