VALENCE AND CORE EXCITATIONS IN RARE-GAS MONOLAYERS AND MULTILAYERS - PRODUCTION, DECAY, AND DESORPTION OF NEUTRALS AND IONS

The aim of this survey is the understanding of the dynamics of medium to high energy excitations in simple condensed systems on very short time scales. For this purpose we examine the modifications of the electronic excitations and their evolution in rare gases (mainly Ar and Kr) due to a nearby metal surface (monolayer case) or by embedding into a rare gas condensate (multilayers). Ionic excitations are shifted to lower energies compared to the gas phase by polarization of the surroundings, while neutral excitations stay constant or are shifted to somewhat higher energies. This decreases the spacing between excitonic and ionic states from both sides. Deexcitation events can be analysed by linewidths for valence excitations, and by comparison of autoionisation and Auger spectra for core excitations. For monolayers, we conclude that excitonic states are unstable relative to ionic states but nevertheless are quite long-lived. For multilayers, only minor modifications relative to the gas phase are usually found. All electronic excitations in Ar and Kr mono- or multilayers lead to desorption of neutrals; core excitations in multilayers also lead to ions and cluster ions. The probable mechanisms in all cases are discussed, and open questions are pointed out. © 1990 Springer-Verlag.