Modification of vapor sensitivity in ellipsometric gas sensing by copper deposition in porous silicon

The sensitivities of porous silicon layers modified by copper deposition to low vapor concentrations of methanol, ethanol and 2-propanol are studied with spectroscopic ellipsometry. The porous silicon layers are prepared with electrochemical etching in hydrofluoric acid, and copper deposition is done in aqueous CuSO4. The ellipsometric vapor sensitivities, in terms of the ellipsometric spectral shifts due to gas exposures, of these samples and their oxides are studied and compared. It is shown that ellipsometric vapor sensitivities of porous silicon layers to alcohols are improved by copper deposition. It is also found that the oxidation of copper deposited in porous silicon layers shows improved selectivity to methanol.