Wafer-scale electroactive nanoporous silicon : large and fully reversible electrochemo-mechanical actuation in aqueous electrolytes
Nanoporosity in silicon results in interface-dominated mechanics, fluidics, and photonics that are often superior to the ones of the bulk material. However, their active control, for example, by electronic stimuli, is challenging due to the absence of intrinsic piezoelectricity in the base material. Here, for large-scale nanoporous silicon cantilevers wetted by aqueous electrolytes, electrosorption-induced mechanical stress generation of up to 600 kPa that is reversible and adjustable at will by potential variations of ≈1 V is shown. Laser cantilever bending experiments in combination with in operando voltammetry and step coulombmetry allow this large electro-actuation to be traced to the concerted action of 100 billions of parallel nanopores per square centimeter cross-section and determination of the capacitive charge–stress coupling parameter upon ion adsorption and desorption as well as the intimately related stress actuation dynamics for perchloric and isotonic saline solutions. A comparison with planar silicon surfaces reveals mechanistic insights on the observed electrocapillarity (Hellmann–Feynman interactions) with respect to the importance of oxide formation and wall roughness on the single-nanopore scale. The observation of robust electrochemo-mechanical actuation in a mainstream semiconductor with wafer-scale, self-organized nanoporosity opens up novel opportunities for on-chip integrated stress generation and actuorics at exceptionally low operation voltages.
laser cantilever bending
European Research Council (ERC)
Centre for Molecular Water Science CMWS
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This work was supported by the Deutsche Forschungsgemeinschaft (DFG) within the Collaborative Research Initiative SFB 986 “Tailor-Made Multi-Scale Materials Systems” Project number 192346071. This project has also received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 964524 EHAWEDRY: “Energy harvesting via wetting-drying cycles with nanoporous electrodes” (H2020-FETOPEN-1-2021-2025). The authors also acknowledge the scientific exchange and support of the Centre for Molecular Water Science CMWS, Hamburg.
Advanced Materials - Wafer%u2010Scale Electroactive Nanoporous Silicon Large and Fully Reversible.pdf