Correlation between Vickers microhardness, porous layer thickness and porosity in p-type nanostructured silicon

Mechanical characteristics via Vickers microindentation technique of nanostructured silicon films have been studied. The samples were grown by the usual electrochemical etching process in presence of hydrofluoric acid in two distinct proportions and for several exposure times. The current density was kept constant for all runs. Porosity and porous layer thickness were measured by gravimetric and optical means, respectively. A linear relation between layer thickness and exposure time shows up, in accordance with previous studies. Correspondingly, a slight decrement in the Vickers hardness is observed. On the contrary, the porosity remains independent of exposure time. A possible explanation is therefore proposed and discussed.