Study of CO surface diffusion on COW(111) by analysis of CO+ field ion rate fluctuations

An analysis of field ion rate fluctuations is proposed for studying the mechanism of the reactive imaging gas supply in a field ion microscope (FIM). In the experiment CO+ ions emitted from a few selected surface sites of the apex plane of a [111]-oriented W tip and mass-to-charge resolved in a magnetic sector field are registered. The CO+ ion rate fluctuations are analyzed by a method developed by Gomer for analyzing field electron current fluctuations. The CO gas supply toward the probed surface sites is found to have a diffusion character, confirming the role of the weakly bound CO layer in the localized field ionization of CO used as imaging gas in a FIM.