A prerequisite for conducting valid corrosion experiments byin situelectron microscopy techniques is not only the achievement of UHV background pressure conditions at the site of the specimen but also the ability to clean the surface of the thin metal substrate specimen before initiation of the corrosive interaction. A miniaturized simple ion gun has been constructed for this purpose. The gun is small enough to be incorporated into an UHV electron microscope specimen chamber with hot stage in such a way as to permit bombardment of the substrate specimen while observing it by transmission electron microscopy TEM. It is shown that the ion beam generated is confined well enough to cause a sputtering removal of substrate material at a rate of approximately 5–10 Å/min and to prevent the sputter deposition of contaminating material from the specimen holder. Thin single crystal Ni (100) film samples were used to demonstrate the applicability of the sputter cleaning technique, to show the removal of ion beam induced radiation damage by annealing, and to evaluate preliminary oxidation tests by selected zone dark-field microscopy.