A phosphine detection matrix using nanostructure modified porous silicon gas sensors

We discuss the selective modification of porous silicon (PS) conductometric gas sensors for phosphine detection. Tin, nickel, copper and gold are electrolessly deposited onto nanopore covered microporous porous silicon surfaces forming SnOx, NiO, CuxO and AuxO nanostructured centers. Further studies have also been carried out with nanostructured alumina coated porous silicon. The porous silicon surface is analyzed for the metal oxides considered using XPS measurements. These experiments demonstrate that the indicated metals are deposited to the nanopore covered micropores of the PS interface and are oxidized to form metal oxide sites. The sensitivity change of these modified porous silicon gas sensor surfaces has been measured under 1–5 ppm PH3 exposure. An improved sensitivity, of the order of 5 times that of untreated porous silicon, for 1 ppm exposure is observed. The selection of the nanostructure deposition is based on the hard to soft acid character of the nanostructured deposit and its subsequent effect on the physisorption of PH3, an intermediate base. The observed behavior follows an inverse pattern IHSAB to the hard soft acid–base concept.