Adsorbate-adsorbate interactions in Na covered Mg surfaces

We present a study on alkali cluster formation induced by ion bombardment, the information being obtained by Collisionally Excited Autoionization Electron Spectroscopy (CEAES). We show that a uniform alkali film on a metal surface can be easily converted in large patches by low energy ion bombardment. The observed phenomenon is coverage dependent, in fact, for alkali density below a critical value the adlayer is uniformly removed. Beyond this critical value a rearrangement mechanism leads to the formation of extended adatom aggregates revealed by the splitting in two components of both Ne and Na autoionization lines. A Mg atomic structure is also revealed in the spectrum, and, according to our interpretation model, no splitting is observed for this peak due to slow excited atoms.