Affiliation: | a Facultat de F?´sica (ECM and ICC), Universitat de Barcelona, Diagonal 647, 08028 Barcelona, Spain b Institute of Physical Chemistry, Polish Academy of Sciences, ul. Kasprzaka 44/52, 01-224 Warsaw, Poland c Surface and Microanalysis Science Division, National Institute of Standards and Technology, Gaithersburg, MD 20899-8370, USA |