Nanocatalyst sensitizers by agglomeration of nanofilms

The sensor function of a semiconducting metal oxide, like SnO₂, when used as a chemical gas sensor is based on modification of the chemical and electronic structure of the surface by adsorption and desorption reactions. In native form of these materials, many molecules cause very similar changes in the electrical conductivity or the work function. To differentiate between various molecules and to amplify the response, i.e., to improve the selectivity and the sensitivity, catalysts can be added onto the surface of such materials. A layer of noble metal nanoparticles is an effective and controllable kind of catalyst suitable for this purpose. We present a method to achieve a layer of noble metal, such as Pd, Ag, Pt or Au, nanoparticles on oxide surfaces. We begin with sputtering deposition of an amorphous metal nanofilm of the thickness of about 5 nm. The film is agglomerated to nanoparticles either via direct crystallization by heating, in the case of non-reacting atmosphere, or by growth of oxide crystallites and subsequential reduction of these in a reducing atmosphere. We present also results of characterization of the initial nanofilm and the resulting nanoparticles by X-ray diffraction, electrical conductivity measurement, scanning force microscopy and transmission electron microscopy.