Silicon Flexes Muscles: Giant Electrochemical Actuation in a Nanoporous Silicon-Polypyrrole Hybrid Material

TL;DR

This paper introduces a novel silicon-based hybrid material that exhibits giant electrochemical actuation, surpassing traditional piezoelectric ceramics, with potential applications in bio-actuators due to its small voltage operation and biocompatibility.

Contribution

The study demonstrates a new composite material combining nanoporous silicon and polypyrrole that achieves unprecedented electrostrain and actuation performance.

Findings

Electrostrain is 1000 times larger than in best ceramics.

Electroactuation is driven by nanopore pressure effects.

Operation voltages are as low as 0.4-0.9 V.

Abstract

The absence of piezoelectricity in silicon makes direct electro-mechanical applications of this mainstream semiconductor impossible. Integrated electrical control of the silicon mechanics, however, would open up new perspectives for on-chip actuorics. Here, we combine wafer-scale nanoporosity in single-crystalline silicon with polymerization of an artificial muscle material inside pore space to synthesize a composite that shows macroscopic electrostrain in aqueous electrolyte. The voltage-strain coupling is 3 orders of magnitude larger than the best-performing ceramics in terms of piezoelectric actuation. We trace this huge electroactuation to the concerted action of 100 billions of nanopores per square centimetre cross-section and to potential-dependent pressures of up to 150 atmospheres at the single-pore scale. The exceptionally small operation voltages (0.4-0.9 V) along with the sustainable and biocompatible base materials make this hybrid promising for bio-actuator applications.