Etching silicon wafer without hydrofluoric acid

A one-step hydrofluoric-acid-free hydrothermal-etching technique is demonstrated for the preparation of porous silicon with vertical holes. This method demonstrates a “green” chemical approach for etching a silicon wafer or the preparation of bismuth-silicon nanostructures without toxic acid or applying an external voltage. By controlling the heating temperature (<180°C) and time, nanoscale vertically holed porous silicon has been created. A formation mechanism has been proposed on the basis of experimental observations.