Characterization of Ca aggregates on CaF2(111)-surfaces by atomic force, XPS, and fluorescence microscopy

In this contribution we report on the metallization of (111)-surfaces of CaF2single crystals as a result of low energy electron irradiation. An in-situ control of the spatial distribution of the metal coverage was obtained by rapidly scanning a low intensity electron beam across the irradiated area and monitoring the STE luminescence radiation. Metallized spots are identified by a reduced luminescence intensity. Surface stoichiometry was tested by XPS-microscopy. The spatially resolved observation of line intensities as well as line shifts revealed an effective metallization and oxidation of the surface. Using atomic force microscopy we found evidence for a 3-dimensional island-like formation of Ca aggregates with a size up to 12 μm diameter. Results for cluster formation in the center of the irradiating beam are compared to those from outer regions. The size distribution of the aggregates reproduces the different levels of electron dosage across the beam profile.