In-situ observation of surface modification induced by highly charged xenon ions on graphite surfaces

R. Minniti, L.P. Ratliff, and J.D. Gillaspy
National Institute of Standards and Technology, Gaithersburg, MD 20899

Highly Charged Ions (HCIs) can store large amounts of internal potential energy (e.g. 6,500 eV for a Xe23+ projectile ion; 50,000 eV for Xe44+) which can be transferred during a collision, to a surface resulting in surface modification. In the present work we have studied the surface modification of highly oriented pyrolitic graphite (HOPG) samples, induced by HCIs.

Highly charged xenon ions were extracted from the NIST Electron Beam Ion Trap (EBIT) and transported, via a beamline, into a UHV experimental chamber where the samples are exposed. The UHV chamber is equipped with a UHV STM which allows performing in-situ observation of surfaces that have been exposed to the ion beam.

STM observation of the exposed surfaces shows the formation of nanometer scale features resulting from HCI-surface interaction; the observed features corresponding to single ion impacts. The diameter of the observed ion-induced nanometer scale features varies with the charge of the ion, and therefore with its potential energy: Xe23+ ions create features on the graphite surface that are 3nm in diameter while features created by Xe44+ ions are 6nm. These results plus a current understanding of the ion-induced surface modification will be presented.