Porous Silicon Preparation by Electrochemical Etching in Ionic Liquids

Anodic etching of n-type {111} silicon in ionic liquid (IL) systems ([RMIM]­[X], R = H, Bu; X = BF4 –, PF6 –), realized under galvanostatic conditions and at room temperature, allowed the formation of porous silicon surfaces with different pore morphology depending on the etching time, current density, and the IL used. The study of the effect of water content in IL on the etching process has shown a water content of 1% to be optimal. The role of the anion on the etching process was elucidated using 1-methylimidazolium tetrafluoroborate ([HMIM]­[BF4]) and 1-methylimidazolium hexafluorophosphate ([HMIM]­[PF6]) IL systems. [HMIM]­[BF4] was found to be most efficient for the formation of a silicon nanostructured array with a pore size of 30–80 nm. The thus-prepared porous silicon samples show fluorescence in blue light (475 nm). The NMR spectra of [HMIM]­[BF4] ionic liquid before and after etching do not show noticeable changes, which makes it possible to consider this IL as a potentially recyclable etching agent.