Sacrificial gold coating enhances transport of liquid metal in pressurized fountain pen lithography

Abstract

Liquid metals have attracted attention as functional components for moldable electronics, such as soft flexible connectors, wires or conductive ink. The relatively high surface tension (> 400 mN m−1) and the fact that liquid metals do not readily wet ceramic or oxide surfaces have led to devising unique techniques to spread the liquid and mold its shape. These techniques include surface modification, electrowetting and vacuum filling of channels. This work presents an injection technique based on pressurized fountain pen lithography with glass nanopipettes developed to directly pattern liquid metal on flat hard substrates. The liquid metals were eutectic alloys of Gallium, including Gallium-Indium (EGaIn), Gallium-Indium-Zinc and Gallium-Indium-Tin. The nanopipettes were coated internally with gold, acting as a sacrificial layer and facilitating the wetting of the pipette down to its pore, with an inner diameter of ~ 100–300 nm. By applying hydrodynamic pressure to the connected end of the pipette, the metal was extruded through the pore, forming long continuous (> 3 mm) and narrow (~ 1–15 µm) metal lines on silicon oxide and gold surfaces at room temperature and ambient conditions. With this robust platform, it is possible to pattern liquid metals on a variety of substrates and geometries down to the micron range.

Enhanced charge transport across molecule–nanoparticle–molecule sandwiches

“…It is noted here that we were unable to obtain any meaningful data when we attempted the fabrication of Au-ML-GNP-eGaIn junctions, most probably due to the formation of intermetallic Au-Ga alloys enabled by the absence of a ligand shell surrounding the Au nanoparticles. 31 The unexpectedly enhanced conductance for the Au-ML-GNP-ML structure was analysed to establish whether it also occurs for different monolayer lengths. Electrical data is shown in Fig.…”

“…It is noted here that we were unable to obtain any meaningful data when we attempted the fabrication of Au–ML–GNP–eGaIn junctions, most probably due to the formation of intermetallic Au–Ga alloys enabled by the absence of a ligand shell surrounding the Au nanoparticles. 31…”

High‐Resolution Capillary Printing of Eutectic Gallium Alloys for Printed Electronics

“…After this initial conditioning, the flow rate was maintained low enough to hold the LM at the capillary tip and patterns are fabricated by bringing the tip in close proximity to the substrate. While coating of capillary with Au can improve the flow of LM, [ 42,43 ] we generally omitted such coatings here, to avoid amalgamation.…”

“…The minimum width of homogeneous, well-defined lines achieved in our approach is (1.3 ± 0.1) µm (Figure S2, Supporting Information), slightly smaller than in previous reports. [19,32,43,44] This high-resolution LM deposition was achieved using a tip of 2 µm opening and a writing speed of 1000 µm s −1 . Printing velocity and tip size can further control the width of the lines.…”

Recent progress in liquid metal printing and its applications

“…Fig.1(a) Schematic diagram of liquid metal nanotip traction device using triaxial piezoelectric stage 3. (b) Transport of liquid metal in pressurized fountain pen lithography 5. (c) Stencil printing and centrifugal force-assisted patterning 4.…”