An AFM investigation of the deposition of nanometer-sized rhodium and copper clusters by spin coating

Abstract

We have used atomic force microscopy to investigate the deposition of nanometer-sized clusters by spin coating and it is shown that it is possible to produce a homogeneous distribution of nanometer-sized Cu and Rh particles using this technique. However, the formation of particles with a uniform size and distribution is not only dependent on the solute concentration and spin frequency, as has been discussed previously, but also on a number of other factors, including: atmospheric humidity, solvent properties and the chemistry of the solute. In the case of the simple salts, Cu(NO 3) 2 and RhCl 3 dissolved in ethanol, particles precipitate out of the solution during spin coating and deposit onto 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 existence of a larger metastable super-saturated region in the Cu(ac) 2 solution resulting from the presence of the acetate ligands. The layer of Cu(ac) 2 is observed to form particles on calcination, the particle size and distribution being sensitive to the calcination rate. Possible factors responsible for the ramp rate sensitivity are discussed. AFM imaging of the surface following oxidation and reduction of the larger Rh particles indicate that these particles break up as a result of the treatment, where this behaviour is consistent with previous studies. Following this treatment, or after direct reduction in H 2, the Rh particles are observed to exhibit a particle-substrate interaction, indicated by the inability of the AFM to sweep the particles across the surface. A similar behaviour is also determined to occur following oxidation of the Cu particles.