Electrochemical printing:in situcharacterization using an electrochemical quartz crystal microbalance

Electrochemical printing (EcP) is a multi-scale freeform fabrication method employing localized electrodeposition beneath a rastering microjet print head flying microns above the deposition substrate. As a result of the confined geometry and unusual electrochemical configuration, conventional in situ diagnostics are difficult to implement. We show that EcP microfabrication on an electrochemical quartz crystal microbalance (EQCM) allows in situ characterization of the electrochemical processes occurring locally beneath the microjet print head and over large patterned areas where corrosion occurs. Copper deposition experiments show the microjet print head can produce extraordinary mass transfer limiting currents (in excess of 10 A cm −2 ). The current efficiency for EcP patterning of copper on gold is limited by oxygen reduction at low applied currents and by hydrogen evolution at high currents. Nonetheless, the maximum current efficiency is >90% over two orders of magnitude change in microjet flow rate; the limiting current varies five-fold over the same flow rates. Calibration of the EQCM local sensitivity factors allows characterization and control of corrosion rates when printing extended patterns.