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Production of hollow atoms (ions) in HCI-surface collision

The interaction of slow highly-charged ions with surfaces is studied using thin Al2O3 and Ni microcapillary foils as targets as well as flat metal plates. The former provides information on hollow atoms (ions) in the first generation (i.e., above surface). In contrast, the latter is suitable to investigate those in the second generation (i.e., at or below surface). About 1% of 2.1 keV/u N6+ ions transmitted through the microcapillary are found to capture at least one electron, which is consistent with the prediction of the classical over-barrier model. The charge state distribution is found to be a very weak function of the exiting charge, which is quite different from that transmitted through a thin foil or that specularly reflected from a surface. N and Ne K x-rays emitted from the downstream of the target show that ~1% of the charge changed ions are in extremely stabilized states with lifetimes of ~ns keeping an innershell orbital open. Further, the relaxation dynamics of hollow atoms in the second generation are studied through measurements of L-X-rays from Ar ions as a function of L-shell hole numbers.