Communication—supercritically-dried membranes and powders of >90% porosity silicon with pore volumes exceeding 4 cm³g^-1

Porous silicon structures can display full biodegradability into orthosilicic acid and are under development for medical uses such as drug delivery. Here we demonstrate optimized electrochemical etching and drying conditions to achieve ultrahigh porosity structures ("silicon aerocrystals"), which should enable ultrahigh nanostructured drug payloads. Supercritical drying (SCD) of detached 41 to 210 micron thick films from etched p ⁺ wafers generates structures with pore volumes 3.5 to 5.13 cm³ g⁻¹, average pore diameters of 29 nm to 35 nm and surface areas 425 to 549 m² g⁻¹. For anodized p ⁺ wafers, the benefits of SCD vs air drying (AD) are primarily elevated pore volumes.