Directed nanoscale metal deposition by the local perturbation of charge screening at the solid–liquid interface†

Understanding and directing electrochemical reactions below the micrometer is a long-standing challenge in electrochemistry.
Conning reactions to nanoscale areas paradoxically requires both isolation and communication with the bulk electrolyte in
terms of potential and access of ions, respectively. Here, we demonstrate the directed electrochemical deposition of copper
nanostructures by using an oscillating nanoelectrode operated with an atomic force microscope (AFM). Strikingly, the writing is
only possible in highly dilute electrolytes and for a particular combination of AFM and electrochemical parameters. We propose
a mechanism based on cyclic charging and discharging of the electrical double layer (EDL). The extended screening length and
slower charge dynamics in dilute electrolytes allows the nanoelectrode to operate inside, and disturb, the EDL even for large
oscillation amplitudes (~100 nm). Our unique approach can not only be used for controlled additive nano-fabrication but also
provides insights into ion behavior and EDL dynamics at the solid-liquid interface.