Molecular dynamics study of direct localized overpotential deposition for nanoscale electrochemical additive manufacturing process

A quasi-deterministic molecular dynamics simulation was performed to study the migration and deposition of ions under the influence of charged, constant-potential electrodes. The input parameters that were varied include tool size, tool potential, substrate potential, interelectrode gap, and concentration. The output parameters of the deposit that were monitored included deposition height over time, number of atoms deposited over time, averaged current density, and deposition quality. Variation of the interelectrode gap or concentration resulted in changes to the deposition rate and quality that were inversely related to each other. It was found that there is an optimal radius to simultaneously maximize deposition speed and quality. An increase in the voltage difference between the tool and substrate improved the rate and overall quality of the deposition, but the highest voltage differences between the electrodes led to a hollow region in the center of the deposit due to ion depletion. Low concentration similarly led to ion depletion conditions. A low amount of anode-cation interactions due to a small tool or low concentration resulted in a deposit that engulfed the tool due to less overall electrostatic interactions repelling the cations from the tool. It was found that an increased output current density did not necessarily coincide with increased output deposit quality.