AN AFM INVESTIGATION OF THE DEPOSITION OF NANOMETER-SIZED RHODIUM ANDCOPPER CLUSTERS BY SPIN-COATING

We have used atomic force microscopy to investigate the deposition of nanometer-sized clusters by spin coating and it is shown that it is po ssible to produce a homogeneous distribution of nanometer-sized Cu and Rh particles using this technique. However, the formation of particle s with a uniform size and distribution is not only dependent on the so lute concentration and spin frequency, as has been discussed previousl y, but also on a number of other factors, including: atmospheric humid ity, solvent properties and the chemistry of the solute. In the case o f the simple salts, Cu(NO3)(2) and RhCl3 dissolved in ethanol, particl es precipitate out of the solution during spin coating and deposit ont o the substrate. However, AFM and XPS analysis reveals that the use of a Cu(acetate)(2) precursor results in the formation of a layer of Cu( acetate)(2) on the substrate. This behaviour is attributed to the exis tence of a larger metastable super-saturated region in the Cu(ac)(2) s olution resulting from the presence of the acetate ligands. The layer of Cu(ac)(2) is observed to form particles on calcination, the particl e size and distribution being sensitive to the calcination rate. Possi ble factors responsible for the ramp rate sensitivity are discussed. A FM imaging of the surface following oxidation and reduction of the lar ger Rh particles indicate that these particles break up as a result of the treatment, where this behaviour is consistent with previous studi es. Following this treatment, or after direct reduction in H-2, the Rh particles are observed to exhibit a particle-substrate interaction, i ndicated by the inability of the AFM to sweep the particles across the surface. A similar behaviour is also determined to occur following ox idation of the Cu particles.