The production of a novel stain-etched porous silicon, metallization of the porous surface and application in hydrocarbon sensors

Novel stain (chemical)-etch solutions based on the strong fluorine-contained acids (fluoroboric (HBF4), hexafluorantimonic (HSbF6) acids, etc.) for the reproducible production of porous silicon (Psi) are described for the first time. The PSi-films, thus produced, exhibit very intense luminescence and are characterized by high thickness homogeneity and of the luminescence characteristics. The etchants do not attack standard photoresist so they have been successfully employed for production of micron-size patterned Psi areas by stain etching through photoresist mask. The Psi, thus produced, has been used as a bearer of catalytic coatings. Platinum and palladium have been successfully deposited onto the Psi, also without current, by the reduction of metal salts in aqueous solutions. The material, thus prepared, has been applied in the manufacture of gas sensors for hydrocarbons, instead of a smooth platinum layer. The sensor testing showed a much quicker response to a changing hydrocarbon concentration in comparison with a smooth platinum sensor and also, less energy consumption. Moreover, such sensors would be relatively cheap to produce commercially in comparison with analogous sensors based on platinum or palladium sponge. (C) 2001 Published by Elsevier Science B.V.