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Published online by Cambridge University Press: 10 February 2011
Sodium-covered silica films formed on silicon substrates have been examined by X-ray photoemission spectroscopy (XPS) and X-ray absorption spectroscopy (EXAFS) in ultra-high vacuumconditions at 300K. The results show that sodium diffuses into the silica layer on a reversible manner and that it modifies the silica network in order to create its own site. Sodium atoms are surrounded by oxygen atoms at an average distance of 2.3 Å and by a second shell which is assigned to silicon atoms located at 3.8 Å. At high Na concentrations, sodium atoms are also present in the close environment of one sodium atom.