Remote Control Electrodeposition: Principles for Bipolar Patterning of Substrates without an Electrical Connection

Abstract

We describe electrolyte design for bipolar electrochemical growth and patterning of a range of materials on an electrically floating substrate using the scanning bipolar cell (SBC). In the SBC, bipolar electrodeposition is driven by local potential variation generated beneath a rastering microjet anode connected to a far-field cathode. Metal reduction occurs beneath the microjet when the substrate is approached, provided the electrolyte possesses a suitable reducing agent that undergoes oxidation across the substrate far-field. We use a series of metal reduction reactions (Ni, Cu, Au, Ag) that cover a wide range of nobility, and couple them to the oxidation of ascorbic acid or ferrous ion, depending upon the metal used. The reversibility or irreversibility of the local metal reduction reaction dictates details of the required electrolyte thermodynamics. For irreversible deposits (Ni, Au), there is a wide thermodynamic operating window for the bipolar counter reaction. Reversible deposits that are easily etched (Cu, Ag) have tight thermodynamic windows; deposit stability requires the use of metastable electrolytes. We provide a simple scaling relationship that incorporates the electrolyte thermodynamics, interfacial charge transfer kinetics, and SBC operating conditions, then demonstrate its use through a 10X reduction in the spatial dimensions of local nickel reduction chemistry.