HICS: Highly charged ion collisions with surfaces
Abstract The layout of a new instrument designed to study the interaction of highly charged ions with surfaces, which consists of an ion source, a beamline including charge separation and a target chamber, is presented here. By varying the charge state and impact velocity of the projectiles separately, the dissipation of potential and kinetic energy at or below the surface can be studied independently. The target chamber offers the use of tunable metal–insulator–metal devices as detectors for internal electronic excitation, a time-of-flight system to study the impact induced particle emission and the possibility to transfer samples in situ to an ultra high vacuum (UHV) scanning probe microscope. Samples and detectors can be prepared in situ as well. As a first example data on graphene layers on SrTiO3 which have been irradiated with Xe36+ are presented.
Kinetic electron excitation in atomic collision cascades.
The kinetic excitation of electrons upon bombardment of a solid surface with energetic ions is investigated. Using a metal-insulator-metal junction, hot electrons produced by the projectile impact are detected with excitation energies well below the vacuum level. The results provide information that cannot be accessed by electron emission experiments. The observed tunneling current depends on the projectile energy and the bias voltage across the junction, opening the possibility of internal excitation spectroscopy.
Surface plasmon de-excitation of multiply charged ions
Electrons in excited states of a multiply charged ion have traditionally been viewed as decaying through Auger processes. Competing with this is photon emission and decay through excitation of the surface plasmon of a solid. The latter is very effective in the energy range 10-30 eV. Utilising part of the available neutralisation energy it leads to a reduction in the number of ejected Auger electrons. For larger energies the photon emission dominates all the other processes.