Hollow Atoms (discovered in 1990 by a French team of researchers around Jean-Pierre Briand) are short-lived multiply excited neutral
atoms
Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons.
Every solid, liquid, gas, an ...
which carry a large part of their Z electrons (Z ... projectile nuclear charge) in high-n levels while inner shells remain (transiently) empty. The hollow atoms are exotic atomic species whose all, or most, electrons lie in excited states, while the innermost shells are empty.
These atomic species were first observed during the interaction of highly charged ions with surfaces.
population inversion
In science, specifically statistical mechanics, a population inversion occurs while a system (such as a group of atoms or molecules) exists in a state in which more members of the system are in higher, excited states than in lower, unexcited energ ...
arises for typically 100
femtoseconds
A femtosecond is a unit of time in the International System of Units (SI) equal to 10 or of a second; that is, one quadrillionth, or one millionth of one billionth, of a second. For context, a femtosecond is to a second as a second is to about 31. ...
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
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 Picometre, picometers to 10 Nanometre, nanometers, corresponding to frequency, ...
, 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
In physics, sputtering is a phenomenon in which microscopic particles of a solid material are ejected from its surface, after the material is itself bombarded by energetic particles of a plasma or gas. It occurs naturally in outer space, and can ...
and the formation of
nanostructures
A nanostructure is a structure of intermediate size between microscopic and molecular structures. Nanostructural detail is microstructure at nanoscale.
In describing nanostructures, it is necessary to differentiate between the number of dimensi ...
on a surface.
External links
Review articleon hollow atoms.
EU Network ITS-LEIFMPI Heidelberg, GermanyTU Wien, Austria
Atomic physics
References
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