Article
Laser-Ultrasonics Reveals the Complex Mechanics of Nanoporous Silicon (en)
* Presenting author
Abstract:
The self-organized formation of 100 billions of parallel nanopores per square centimeter cross section in nanoporous silicon leads to completely new functionalities of this mainstream semiconductor with numerous discoveries in fields ranging from nanofluidics and biosensorics to drug delivery, energy storage and photonics. Nevertheless, the mechanical properties, critical for a variety of applications, remain difficult to characterize comprehensively. In a recent study, we addressed this issue by utilizing laser-excited elastic guided waves, detected in dry and liquid infused porous silicon [1]. Among the key findings, we observed an 80% effective reduction in stiffness, alongside a notably higher stiffness along the pore axis compared to bulk silicon. Furthermore, these experiments provided insights into the intricate geometry of the pores: The high sensitivity of guided waves with regard to symmetry revealed the pores’ conicity, which is unintentionally generated during the electrochemical synthesis. This thorough assessment of the wafer-scale mechanics of nanoporous silicon and recent breakthroughs in laser ultrasonics therefore enabled us to further optimize the synthesis of porous silicon and open up entirely new frontiers for in-situ, non-contact and non-destructive mechanical characterization of complex porous material systems.[1] Thelen, M., Bochud, N. et al., Nat Commun., 12, 3597 (2021)