MOLECULAR SPUTTERING AND DAMAGE INDUCED BY KILOELECTRONVOLT IONS IN ORGANIC MONOLAYER METAL SYSTEMS

Irradiation experiments, using kiloelectronvolt Cs+ primary ions, have been carried out on Langmuir-Blodgett monolayers adsorbed on Au substrates. From these experiments, disappearance cross-sections, sigma, of the ejected molecular ion have been deduced; sigma corresponds to the monolayer surface area from which molecules are ejected or damaged by the impact of the primary ion. The influence of many parameters-energy and angle of incidence of the primary ion, thickness and density of the monolayer-on the disappearance cross-sections has been investigated. The results clearly show that sigma linearly depends on the energy lost by the primary ion passing through the monolayer. The energy lost in the substrate is not involved in the ejection and the damage of molecules. These results are not consistent with an ion ejection directly induced by collision cascades in the organic monolayer. They rather suggest the formation of a vibrationally excited region prior to ion ejection.