Effects of electron irradiation on the structure and morphology of CaF2/Si(111)

With the use of X-ray Standing Waves (XSW) and Atomic Force Microscopy (AFM ), we have studied the structure and morphology of CaF2 films (thickness ra nge 3-15 Angstrom) grown on Si(111) before and after modification by electr on irradiation. The Ca monolayer of the as-grown CaF2 monolayer relaxes tow ards the Si substrate. The F bilayer embedding the Ca monolayer has bulk sp acing. Low Energy (80-100 eV) Electron-Stimulated Desorption (ESD) of fluor ine reduces mainly the occupation of the top F layer due to generation of s urface color centers. The Ca layer is affected only marginally by the elect ron bombardment. For 15 Angstrom, CaF2 films the color centers nucleate and form Ca clusters embedded in the film. These clusters are removed under am bient conditions (pin hole formation). Inspection of the holes shows that t he Ca clusters penetrate the entire CaF2 film. (C) 2000 Elsevier Science B. V. All rights reserved.