Hollow Atoms are short-lived multiply excited neutral atoms which carry a large part of their Z electrons (Z ... projectile nuclear charge) in high-n levels while inner shells remain (transiently) empty. This population inversion

Population inversion

In physics, specifically statistical mechanics, a population inversion occurs when a system exists in state with more members in an excited state than in lower energy states...

  arises for typically 100 femtoseconds during the interaction of a slow highly charged ion (HCI) with a solid surface.
Despite this limited lifetime, the formation and decay of a hollow atom can be conveniently studied from ejected electrons and soft X-rays, and the trajectories, energy loss and final charge state distribution of surface-scattered projectiles. For impact on insulator surfaces the potential energy contained by hollow atom may also cause the release of target atoms and -ions via potential sputtering

Sputtering

Sputtering is a process whereby atoms are ejected from a solid target material due to bombardment of the target by energetic particles. It is commonly used for thin-film deposition, etching and analytical techniques .-Physics of sputtering:...

 and the formation of nanostructures on a surface.

External links

• Short movie on hollow atom formation.
• Review article on hollow atoms.
• EU Network ITS-LEIF
• MPI Heidelberg, Germany
• NIST, USA
• TU Wien, Austria