Nanoscale Controlled Oxidation of Liquid Metals for Stretchable Electronics and Photonics

Abstract

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.

Biomaterial‐Based Solid‐Electrolyte Organic Electrochemical Transistors for Electronic and Neuromorphic Applications

“…[51] Finally, the gate electrode was made of gallium-indium eutectic (GaIn), a liquid metal, drop-casted onto the gels. GaIn was used because of its potentials in flexible and stretchable electronics: liquid metals have been made into stretchable films as thin as 90 nm with a resistance stable after ten thousand cycles, [52] as well as have shown excellent compatibility with printing processes, [53] which makes them attractive for the fabrication of stretchable OECTs. [27,54] Besides, the formation of a native thin Ga 2 O 3 overlayer on GaIn gate would prevent the gate from participating in redox reactions at the gel/electrolyte materials, [55] avoiding possible degradation and allowing the study to focus on the role of biogel electrolytes in the working mechanism of OECTs.…”

Novel insights into the design of stretchable electrical systems

“…on July 13, 2021 http://advances.sciencemag.org/ Downloaded from experimental and simulated data highlights the validity of the proposed model. Besides the random structures from (18), this constant resistance behavior has never been demonstrated to our knowledge at extended deformations (>~30%), and moreover with intrinsically stretchable materials. Given the high conductivity of liquid metals compared with other state-of-the-art stretchable composites such as embedded silver nanowire networks (32), the proposed approach enables the design and fabrication of microstructures with both tailored response and reduced size footprint, a critical point given the increasing miniaturization of integrated systems.…”

Tunable Metasurfaces: The Path to Fully Active Nanophotonics

“…[ 258,259 ] The toxicity and biodegradability of materials are important in the biomedical field, and extra limitations on how the modulation mechanisms can be achieved exist due to the interaction with human subjects. Therefore, tunable metasurfaces based on non‐toxic liquids such as water could offer a potential solution, [ 190,260–263 ] as could the use of organic materials such as chitosan for the active components. [ 264 ] For applications, such as invisibility cloaking, passively reconfigurable metasurfaces could be a key in hiding a target without any external intervention.…”

“…Adapted with permission. [ 190 ] Copyright 2020, Wiley‐VCH GmbH. d) A metalens fabricated on stretchable PDMS.…”

“…[ 189 ] Metasurfaces using this material with a stretchable PDMS substrate to create a resonance peak in the IR regime have been produced (Figure 7c). [ 190 ] The oxidation and substrate states were carefully controlled to allow for the deposition of thin films of liquid gallium. The films were then combined with standard nanofabrication techniques, such as lithography, to realize the meta‐atoms to create metasurfaces with optical responses in the IR region.…”