Laser Writing of Eutectic Gallium–Indium Alloy Graphene‐Oxide Electrodes and Semitransparent Conductors

Abstract Graphene encapsulated liquid metal particles is a novel and promising class of biphasic composite, with application in the next generation of electronic devices. Here, rapid, low‐cost, and scalable fabrication of solution processed large area rGO@EGaIn electrodes is demonstrated. rGO@EGaIn solution is first deposited over the substrate through spray coating, and then processed through a low‐cost laser (master oscillator power amplifier (MOPA)). This allows simultaneous reduction, thinning, ablation, and high resolution patterning of the deposited films. Surprisingly, it is found that by adjusting the laser parameters, it is possible to make semitransparent conductors via laser thinning of the films. Scanning electronic microscopy (SEM) and energy dispersive X‐ray spectroscopy (EDS) spectroscopy confirm that although the rGO/EGaIn weight ratio is only ≈0.08, the composite has a considerably different microstructure compared to the eutectic gallium–indium alloy (EGaIn) particles alone. Graphene oxide (GO) protects the EGaIn from extreme morphology change under laser irradiation. Therefore, various “shades” of rGO@EGaIn can be fabricated in a single film. This allows development of large electrodes with complex geometries in a few seconds. The conductivity, transparency, and reduction of the laser processed films are characterized by several techniques and an example of application is demonstrated by laser patterning a highly sensitive breath‐monitoring sensor.