  A grand challenge of nanoscience is to master the control of structure and
properties in order to go beyond present day functionality. The creation of
nanostructures via atom manipulation by means of a scanning probe represents
one of the great achievements of the nano era. Here we build on this
achievement to self-assemble nanostructures within quantum corrals. The
structuring is guided by the quantum confinement of the electronic density of a
silver metallic substrate within the corrals. We experimentally demonstrate
different self-organized Gd atomic structures confined within 30-nm circular
and triangular Fe quantum corrals. This approach enables the creation of model
systems to explore and understand new nanomaterials and device prototypes.
