Negative ion formation in the scattering of atoms and ions from dielectricsurfaces

Interaction of atomic and molecular particles with dielectric surfaces has been attracting considerable attention over the past years, in order to und erstand various fundamental problems important in catalysis, development of gas sensors, problems of adhesion etc. Detailed quantitative information a bout the dynamics of electron transfer, which plays an important role in ch emisorption and reactions at surfaces, has been recently obtained from expe riments in which ionic or atomic beams are scattered off dielectric surface s and the charge states of particles are analysed, providing in particular site-specific information on electron transfer. These experiments have show n that the dynamics of electron transfer on semiconductor and insulator sur faces cannot be understood within simple models extensively used for the ca se of metal surfaces. It was shown in particular that in spite of the exist ence of large bandgaps and at first sight the unfavourable situation for re sonant electron transfer, negative ion formation occurs quite efficiently. Together with the existence of an efficient electron capture process associ ated with negative ion formation the existence of electron loss processes w as demonstrated by use of both atoms and negative ions as projectiles. Vari ous theoretical descriptions for describing electron capture and loss pheno mena have been developed. In this review the experimental approaches and re sults are outlined along with the theoretical concepts and approaches devel oped to treat electron transfer phenomena on dielectric surfaces.