Laser-Excited Elastic Guided Waves Reveal the Complex Mechanics of Nanoporous Silicon

Abstract

Nanoporosity in silicon leads to completely new functionalities of this mainstream semiconductor. A difficult to assess mechanics has however significantly limited its application in fields ranging from nanofluidics and biosensorics to drug delivery and energy storage. Here, we present a study on laser-excited elastic guided waves detected contactless and non-destructively in dry and liquid-infused single-crystalline porous silicon.These experiments reveal that the selforganised formation of 100 billions of parallel nanopores per squarecentimetre crosssection results in a nearly isotropic elasticity perpendicular to the pore axes and an 80% stiffnessreduction in the material, despite a bulk-like and anisotropic porewall elasticity. Our thorough assessment of the wafer-scale mechanics of nanoporous silicon provides the base for predictive applications in robust on-chip devices and evidences that recent breakthroughs in laser ultrasonics open up entirely new frontiers for in-situ, non-destructive mechanical characterisation of dry and liquid-functionalised porous materials.

Here saved are raw and processed data of laser ultrasonics measurements of porous and bulk silicon.