Gold-catalysed porous silicon for NOx sensing

Porous silicon (PS), obtained by electrochemical anodization of an n-type silicon wafer, was catalysed by sputtering gold onto the surface (4, 8, 15 and 40-nm nominal thickness). Investigation by Rutherford backscattering spectroscopy (RBS) and by electron microscopy showed that gold did not form a continuous layer, but rather formed clusters penetrating into the pores of PS by about 1 μm. A variation of the sample conductivity in the presence of a few parts per million of NO2 and NO was recorded at room temperature. We demonstrated that, as a result of Au catalysation, PS is suitable for sensing nitrogen oxides with negligible influence by interfering gases such as CO, CH4 or methanol. Indeed, we found that humidity appreciably affected the response.