Nanocatalyst sensitizers by agglomeration of nanofilms

The sensor function of a semiconducting metal oxide, like SnO2, when used a s a chemical gas sensor is based on modification of the chemical and electr onic structure of the surface by adsorption and desorption reactions. In na tive 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 selecti vity and the sensitivity, catalysts can be added onto the surface of such m aterials. A layer of noble metal nanoparticles is an effective and controll able kind of catalyst suitable for this purpose. We present a method to ach ieve a layer of noble metal, such as Pd, Ag, Pt or Au, nanoparticles on oxi de surfaces. We begin with sputtering deposition of an amorphous metal nano film of the thickness of about 5 nm. The film is agglomerated to nanopartic les either via direct crystallization by heating, in the case of non-reacti ng atmosphere, or by growth of oxide crystallites and subsequential reducti on of these in a reducing atmosphere. We present also results of characteri zation of the initial nanofilm and the resulting nanoparticles by X-ray dif fraction, electrical conductivity measurement, scanning force microscopy an d transmission electron microscopy. (C) 2000 Elsevier Science S.A. All righ ts reserved.