Interaction of slow grazingly incident ions with insulators

Research project P 14337 Interaction of slow grazingly incident ions with insulator surfaces Friedrich AUMAYR 08.05.2000 Ion-induced electron emission from solid surfaces is of considerable principal and practical interest in surface physics and -analytics, and also for various plasma related applications. Electron emission arises as a consequence of inelastic ion - surface collisions and often accompanies other processes like backscattering, energy loss or sputtering. In basic studies of ion-surface collisions the emission of electrons therefore provides one of the keys for explaining the underlying physical processes (e.g. kinetic and potential electron emission). Electron emission processes are closely related to the inelastic energy loss of the projectile ions. A rather detailed understanding of such inelastic interactions can be achieved if trajectories of the scattered ions are well defined, as is the case in grazing incidence scattering geometries. Moreover, scattered ions and emitted electrons can then be studied in coincidence. While metal surfaces have been investigated extensively both experimentally and theoretically, considerably less data are available for insulating targets. Within this project the interaction of singly and multiply charged ions (and in collaboration with HU Berlin probably also neutral atoms) with single - crystal insulator surfaces, in particular LiF(100), will be studied under grazing incidence geometry. An existing coincidence apparatus will be equipped with a time-of-flight system that allows to correlate the energy loss of projectiles grazingly scattered from the crystal surface with the number of electrons emitted during this interaction, as well as with the charge state - and angular distribution of the scattered ions. By such means important new insights into the mechanisms responsible for inelastic ion - surface interactions for insulator surfaces can be obtained.

Ion-induced electron emission from solid surfaces is of considerable principle and practical interest in surface physics and -analytics, and also for various applications (plasma - wall interaction in thermonuclear fusion research, particle counting, etc.). Electron emission arises as a consequence of inelastic ion - surface collisions and often accompanies other processes like backscattering, energy loss or sputtering. In basic studies of ion-surface collisions the emission of electrons therefore provides one of the keys for explaining the underlying physical processes (e.g. kinetic and potential electron emission). Electron emission processes are closely related to the inelastic energy losses of the projectile ions. A rather detailed understanding of such inelastic interactions can be achieved if trajectories of the scattered ions are well defined, as is the case in grazing incidence scattering geometries. Moreover, scattered ions and emitted electrons can then be studied in coincidence. Within this project we have developed an innovative coincidence detector for measuring electron emission as well as projectile energy loss in grazing incidence ion-surface collisions. This setup has been successfully applied to investigate the interaction of singly and multiply charged ions (MCI) with single - crystal insulator surfaces (Vienna part) as well as the interaction of fast neutral atoms with single - crystal insulator and - metal surfaces (Berlin part). The results obtained provide new insight in the basic mechanisms of potential and kinetic electron emission from both insulating and conducting surfaces. We could, e.g., demonstrate that the coincidence technique is a unique tool to evaluate potential electron emission contribution even in the presence of a considerable number of kinetically excited electrons. For atomic projectiles the threshold behaviour of all electron excitation- and emission channels could be determined with unprecedented sensitivity and accuracy. The different response of insulator and metal surfaces found in our experiments have been explained satisfactorily by suitable interaction models developed during the project.