Die Analyse monomolekularer FestkörperoberflÄchenschichten mit Hilfe der SekundÄrionenemission

The use of extremely low primary ion current densities (10^?9 A cm^?2) increases the sputtering time of the original first monolayer of a solid to such a degree (>10⁴ s), that the analysis of this layer by secondary ion spectroscopy can be realized. Changes in its composition (caused by surface reactions, particle bombardment etc.) can be observed for a long period before a considerable fraction of the surface has interacted with the weak ion beam. The capacity of the method is demonstrated by analysis results of Ag and Mo surfaces. Many kinds of ions follow exactly the time dependenceN(t)=N(0)e ^?t/T, characteristic exclusively for ions originating from components present only in the first monolayer. The detection limit for several complex anions is below 1 ppm of a monolayer (<10^?15 g). This method of monolayer analysis shows some advantages compared with electron probe x-ray analysis or Auger electron spectroscopy: Isotope separation, detection of changes of concentration within the first few monolayers, and especially the detection of chemical compounds.