Electrosorption-Induced Actuation in Nanoporous Silicon

Porous silicon provides a scaffold structure to study the confinement related effects of soft matter.

However, the active, mechanical control of porous silicon as a response to an electronic potential is challenging due to the absence of intrinsic piezoelectricity in the silicon base material. Here, for wafer-scale nanoporous silicon cantilevers immersed in aqueous electrolytes, we show reversible electrosorption-induced mechanical stress generation under electrochemical control. The silicon-electrolyte interface acts as a capacitor which allows the accumulation of electrolyte anions in a chemical double layer by an applied voltage, whose characteristics can be measured by cyclic voltammetry. The surface stresses that are caused to the monolithic porous silicon by such an accumulation lead to a macroscopic strain which can be determined in-situ with a laser beam-bending setup. Comparing nanoporous silicon with a planar silicon surface yields insights on the observed electrocapillarity - in particular with respect to the importance of oxide formation and wall roughness on the single-nanopore scale. The presence of robust electrosorption-induced actuation in the mainstream semiconductor silicon combined with self-organized nanoporosity on the wafer-scale facilitates novel opportunities for on-chip integrated stress generation and actuorics at low operating potentials.[1]