Electron and Ion-Induced Reactions of Organic Molecules Adsorbed on the Surfaces

Abstract

The studies on the chemical reactions of organic molecules induced by low-energy electrons and gas cluster ions are reviewed. The author's group has developed the in-situ observation technique for electron-irradiated surfaces. The technique employs a scanning tunneling microscope as a field-emitted electron source, as well as a probe for surface analysis. By using the technique, we have investigated the effect of low-energy-electron irradiations to adsorbed molecules, such as ethylene and DNA. Desorption, dissociation of the molecules and changes to other chemical species, were observed, depending on electron energy and electron dosage. When a gas cluster ion, consisting of thousands of atoms or molecules, collides with a solid surface, several types of reactions are uniquely induced at the surface. The average kinetic energy of a constituent atom of the cluster can be defined by dividing the acceleration energy by the number of constituent atoms. Thus, very low-energy-ion irradiation is easily achieved by using large cluster ions. DNA adsorbed graphite surfaces were irradiated with argon(Ar) gas cluster ions. The secondary ion yield and the structural changes of the surfaces were investigated. These results are compared with the case by the irradiation with monomer ions (Ar+) and are discussed from the view point of the kinetic energy of a constituent atom of the cluster ion.