(328a) Liquid Metal Oxide Annealing for the Simple Generation of Sensing and Electronic Materials

Room temperature liquid metals have recently been a subject of enormous study due to their simultaneous deformable and conductive properties. Liquid metals, largely based on alloys of gallium, have been used as electrode contacts, in microfluidic devices, and in polymer composites for sensors, actuators, and other electronic devices. One consistent piece of this research has been dealing with the native oxide that develops on the liquid metal in an oxygen atmosphere (oxygen concentrations can be as low as ppb and still generate oxide). The oxide significantly increases the viscosity of the liquid metal and alters its surface, interfacial, and wetting properties. While not much is agreed upon in the literature with respect to the liquid metal oxide, it is generally considered to be of a thickness on the order of nanometers and consist largely of gallium oxide. While this oxide may pose significant challenges to most common uses of liquid metal, this work focuses instead on utilizing the liquid metal oxide as an electronic material component. The primary expected composition of galinstan, the room temperature alloy of gallium-indium-tin, is gallium oxide, of the β-Ga₂O₃ form due to highest thermodynamic stability, and SnO­­₂. Both of these materials, when grown in a clean room or sputtered, are highly valued as semiconductors particularly in their thin film form. On liquid metal, these oxides are formed natively and nearly instantaneously with virtually no effort. However, the native oxide is largely amorphous and not enough is known about its mechanical or electrical properties. As such, in this work, the liquid metal oxide is manipulated via annealing and characterized with respect to crystallinity, resistivity, and modulus to evaluate how this native material may be used on the already present (and fully wetted) liquid metal electrode as a semiconductor. It was found that while annealing is highly effective at improving crystallinity, specifically in a manner that is controllable through temperature and duration, confounding effects of changing composition and thickness make simple electrical tuning difficult. However, annealing was found to be an effective way of moving the liquid metal oxide toward a more efficient, potential semiconducting material without completely losing the deformability of the liquid metal.