Single-step aerosol printing of metallic nanostructures via in-flight plasma reduction

Abstract

Direct printing of metallic inks rarely achieves functional conductivity in a single step. Most techniques require post-processing, including solvent removal and particle sintering, which restrict applicability in power-limited systems, heat-sensitive substrates, and rapid fabrication scenarios. In this work, we present a plasma-assisted aerosol printing process that integrates deposition and post-processing into a single step. Using this approach, we demonstrate direct metallization of nickel and copper films using formate-ethylenediamine-based metal organic decomposition (MOD) inks at relatively low temperatures. We further demonstrate that co-printing of precursor inks can produce biphasic alloyed films. Increasing the plasma voltage improves in-flight precursor reduction and lowers the resulting film resistivity. The carrier-gas flow rate controls droplet delivery to the plasma reactive zone and, in turn, film uniformity. The solvent composition sets droplet volatility, which determines whether droplets arrive at the substrate dry and fully reduced or wet and only partially reduced. Layer count controls the transition from continuous conductive films at two passes to hierarchically rough, high-surface-area morphologies at higher counts. The process yields resistivities of 273 μΩ·cm for nickel and 14.4 μΩ·cm for copper, comparable to or lower than values reported for other direct-write techniques. Co-printing of the two inks yields a biphasic film in which discrete metallic Ni is dispersed within a Cu-rich (Cu 0.95 Ni 0.05 ) solid solution. The process-structure relationships established in this work provide a framework for enabling rapid metallization in applications such as space manufacturing, printed electronics, and biocompatible coatings on heat-sensitive substrates.