A microcapillary target as a metastable hollow ion source

Abstract

Interaction of highly charged ions (HCIs) with solid surfaces has been studied with microcapillary metallic foils, which have many straight holes of ∼100 nm in diameter and ∼1 μm in thickness distributed regularly over the foil. It was found that some considerable fraction of ions can pass through the small capillary without suffering violent collisions with the capillary wall but at the same time capturing multiple electrons in their highly excited Rydberg states, i.e. hollow atoms (ions) are effectively extracted in vacuum. The study of ion–capillary interaction now gets even more promising because of new developments of nano-lithographic techniques, which allow preparing highly ordered microcapillaries. The interaction of HCIs with microcapillaries has been studied through (1) visible light measurements, which provide information on the very beginning of the charge transfer processes, (2) soft X-ray measurements, which reveal the electronic configuration at the moment of inner shell filling processes in a later stage and also (3) angular distribution measurements of each charge-changed component, which provide insight on the position of the ion from the inner wall when the charge transfer takes place. It was found that the ion trajectory is not very much deformed during electron transfers, i.e. one can prepare a well-collimated monoenergetic beam of metastable hollow ions (atoms), which is a unique probe carrying high potential energy at relatively low charge states.