  Additive microfabrication processes based on localized electroplating enable
the one-step deposition of micro-scale metal structures with outstanding
performance, e.g. high electrical conductivity and mechanical strength. They
are therefore evaluated as an exciting and enabling addition to the existing
repertoire of microfabrication technologies. Yet, electrochemical processes are
generally restricted to conductive or semiconductive substrates, precluding
their application in the manufacturing of functional electric devices where
direct deposition onto insulators is often required. Here, we demonstrate the
direct, localized electrodeposition of copper on a variety of insulating
substrates, namely Al2O3, glass and flexible polyethylene, enabled by
electron-beam-induced reduction in a highly confined liquid electrolyte
reservoir. The nanometer-size of the electrolyte reservoir, fed by
electrohydrodynamic ejection, enables a minimal feature size on the order of
200 nm. The fact that the transient reservoir is established and stabilized by
electrohydrodynamic ejection rather than specialized liquid cells could offer
greater flexibility towards deposition on arbitrary substrate geometries and
materials. Installed in a low-vacuum scanning electron microscope, the setup
further allows for operando, nanoscale observation and analysis of the
manufacturing process.
