Shape change in nano-structures from AgnOxHy silver cluster deposition on graphite induced by their chemical composition

We have investigated the deposition of AgnOxHy clusters onto a graphite surface, maintained at room temperature, as a function of the cluster chemical composition. The incident clusters were produced by a gas-aggregation silver cluster source when adding O-2 and H2O molecules in the carrier gas, and monitored by a time of flight mass spectrometer. The prepared samples were imaged by electron microscopy. Experimental results show that cluster diffusion and agglomeration on the surface as well as the resulting island morphology strongly depend on the cluster chemical composition. If the deposition of pure silver clusters leads to nano-fractal islands, a few of oxide/hydroxide molecules incorporated as impurities into the incident clusters prior to their deposition induce a postfractal island fragmentation, keeping constant the fractal dimension. However, the deposition of totally oxidized/hydroxided clusters induces a drastic change in island morphology associated with a decrease of the cluster diffusion on graphite. In this last case a dense nano-phase material with narrow size particle distribution agglomerated in chain-like structure is obtained. (C) 2002 Elsevier Science B.V. All rights reserved.