  The fabrication of three-dimensional (3D) nanostructures is of great interest
to many areas of nanotechnology currently challenged by fundamental limitations
of conventional lithography. One of the most promising direct-write methods for
3D nanofabrication is focused electron beam-induced deposition (FEBID), owing
to its high spatial resolution and versatility. Here we extend FEBID to the
growth of complex-shaped 3D nanostructures by combining the layer-by-layer
approach of conventional macroscopic 3D printers and the proximity effect
correction of electron beam lithography. This framework is based on the
continuum FEBID model and is capable of adjusting for a wide range of effects
present during deposition, including beam-induced heating, defocussing and gas
flux anisotropies. We demonstrate the capabilities of our platform by
fabricating free-standing nanowires, surfaces with varying curvatures and
topologies, and general 3D objects, directly from standard stereolithography
(STL) files and using different precursors. Real 3D nanoprinting as
demonstrated here opens up exciting avenues for the study and exploitation of
3D nanoscale phenomena.
