  Nanoscale focused ion beams (FIBs) represent one of the most useful tools in
nanotechnology, enabling nanofabrication via milling and gas-assisted
deposition, microscopy and microanalysis, and selective, spatially resolved
doping of materials. Recently, a new type of FIB source has emerged, which uses
ionization of laser cooled neutral atoms to produce the ion beam. The extremely
cold temperatures attainable with laser cooling (in the range of 100 uK or
below) result in a beam of ions with a very small transverse velocity
distribution. This corresponds to a source with extremely high brightness that
rivals or may even exceed the brightness of the industry standard Ga+ liquid
metal ion source. In this review we discuss the context of ion beam technology
in which these new ion sources can play a role, their principles of operation,
and some examples of recent demonstrations. The field is relatively new, so
only a few applications have been demonstrated, most notably low energy ion
microscopy with Li ions. Nevertheless, a number of promising new approaches
have been proposed and/or demonstrated, suggesting that a rapid evolution of
this type of source is likely in the near future.
