6.

Importance of charge carriers on the purity of deposited structures. Schematic of ejected nanodroplets with a focus on charge carriers, including the depiction of dissolved metal A (pink), charged impurities (blue), H⁺ ions (gray), negatively charged counterions (green), and uncharged species (black). Note that the net charge of the droplet is conserved from ejection until it is reduced on the substrate or until the droplet disintegrates. The same net charge of the droplet can be achieved with various combinations of charge carriers. The specific ion counts shown in the schematics are illustrative only and do not represent experimentally or computationally validated droplet compositions; for an order-of-magnitude estimate of EHD-RP droplet charge, see the recent analysis of the radius-to-charge ratio in acetonitrile. (a) Low metal content and high content of H⁺ or charged impurities leading to a slow deposition of metal structures with large impurity incorporation. (b) High metal content and a minimal presence of H⁺ and charged impurities leading to the highest deposition rate. (c) At very high metal-ion concentrations, negatively charged counterions are coejected and subsequently codeposited. The counts of specific ions is to the right of each nanodroplet, and for all droplets, the net charge is equal.