This highlight describes emerging methods to pattern metals that are liquid at room temperature. The ability to pattern liquid metals is important for fabricating metallic components that are soft, stretchable, conformal, and in some cases, shape-reconfigurable. Applications include electrodes, antennas, micro-mirrors, plasmonic structures, sensors, switches, and interconnects. Gallium (Ga) and its liquid metal alloys are attractive alternatives to toxic mercury. This family of alloys spontaneously forms a surface oxide that dominates the rheological and wetting properties of the metal. These properties pose challenges using conventional fabrication methods, but present new opportunities for patterning innovations. For example, Ga-based liquid metals may be injected, imprinted, or 3D printed on either soft or hard substrates. The use of a liquid metal also enables rapid and facile room temperature processing. The patterning techniques organize into four categories: (i) patterning enabled by lithography, (ii) injection, (iii) subtractive techniques, and (iv) additive techniques. Although many of these approaches take advantage of the surface oxide that forms on Ga and its alloys, some of the approaches may also be suitable for patterning other soft-conductors (e.g., conductive inks, pastes, elastomeric composites).
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