Nanoscale Controlled Oxidation of Liquid Metals for Stretchable Electronics and Photonics

Liquid metals based on gallium have attracted considerable attention for soft and bioelectronics, thanks to their excellent combination of stretchability and conductivity. Nevertheless, owing to their large surface tension, these materials are notoriously difficult to pattern and shape into thin continuous films, or nanoscale 2D architectures, hindering practical use in systems with reduced dimensions. Herein, thanks to fine control in both substrate surface state and oxidation dynamics, a process for producing stretchable gallium-based conducting films with percolation down to 90 nm thickness is presented. By further combining this process with lithography, it is also demonstrated that the approach enables, for the first time, stable stretchable gallium-based optical metasurfaces with tunable resonance in the infrared. It is shown that oxygen partial pressure during evaporation determines the initial film percolation via an interplay between oxidation and dewetting. With this approach, conducting films with relative resistance change as low as 3% over 50% strain, with an excellent stability over 15k cycles are also demonstrated. Tunable soft optical metasurfaces with sub-micrometer feature sizes are also realized, paving the way toward a novel paradigm in soft electronics and photonics.