Tunable Noble Metal Thin Films on Ga Alloys via Galvanic Replacement

Abstract

Room-temperature liquid metals such as GaInSn or EGaIn present the most attractive properties for soft and highly stretchable electronics. Recently, several methods have been investigated to functionalize the surface of the liquid metal via coatings and encapsulation. However, most can hardly be extended to other samples than droplets. In this study, we focus on the tunability of the process of galvanic replacement of Ga alloys with gold to form thin-film encapsulation. We characterized in-depth the obtainable composition and structure of a noble metal shell formed on the liquid metal via scanning electron microscopy, energy-dispersive X-ray, and topographic laser microscopy and highlighted the change in mechanism of galvanic replacement in different pH ranges. We showed the tunability of the surface morphology selection of different pH ranges, the solutions concentrations, and the reaction time. The adjustment of the pH of KAuBr solution to the preferential GaO-free domain led to the successful formation of a sub-micrometer thin uniform coating with more than 60% of Au and reduced level of oxygen from 30% down to 10%. We finally demonstrated the effect of the coating composition on the electrical properties of the liquid metal using a simple and fast phase-drop measurement setup on the droplet and microchannels. A high correlation between the amount of noble metal deposited and the electrical properties of the droplets was demonstrated.

Liquid Metal–Based Soft Microfluidics

“…Gallium‐based alloys swiftly oxidize when exposed to oxygen. Thus, the surface is rapidly covered with a thin layer of gallium oxide—the so‐called oxide skin . Although there are other metals present in the liquid metal alloys, such as indium and tin in Galinstan while their content cannot be neglected (indium content 25%, tin content 10% in Galinstan), the liquid metal surface is mostly covered by gallium oxides due to the reduction of the Gibbs free energy for the generation of gallium oxides .…”

“…Thus, the surface is rapidly covered with a thin layer of gallium oxide-the so-called oxide skin. [12][13][14] Although there are other metals present in the liquid metal alloys, such as indium and tin in Galinstan while their content cannot be neglected (indium content 25%, tin content 10% in Galinstan), the liquid metal surface is mostly covered by gallium oxides due to the reduction of the Gibbs free energy for the generation of gallium oxides. [6] The nanoscale oxide layer possesses an amorphous crystal structure while the thickness of the oxide layer remains constant due to the self-limiting effect of the oxide skin.…”

“…The skin possesses low surface tension while showing high affinity and adhesion to various substrates. LM perfectly combines the conductivity and deformability all‐in‐one, the applications of LM microfluidics in electronics and its derived fields extend the traditional rigid electronics into a whole new level with soft, flexible, stretchable, reconfigurable and even self‐ healable features . Theoretically, the LM in a microfluidic system can be infinitely deformed while maintaining its conductivity.…”

“…LM perfectly combines the conductivity and deformability all-in-one, the applications of LM microfluidics in electronics and its derived fields extend the traditional rigid electronics into a whole new level with soft, flexible, stretchable, reconfigurable and even self-healable features. [12][13][14] Theoretically, the LM in a microfluidic system can be infinitely deformed while maintaining its conductivity. To date, LM-based microfluidics have demonstrated excellent performance in soft, flexible and wearable electronics, soft robotics, biomedical sensors, and transient circuits.…”

Galvanic Replacement of Liquid Metal/Reduced Graphene Oxide Frameworks

“…In the intracellular replacement pattern, the core of LM nanodroplets made a change, and the galvanic replacement of LM nanodroplets was not limited on their surface. [15,18,20,63] Taking advantage of the intracellular galvanic replacement pattern, LM@RGO could be potentially used as the heavy metal ion sensor by anodic stripping voltammetry. To receipt the electrochemical signal, LM@RGO was immobilized onto the carbon papers, and used as the working electrode in the three-electrode system.…”