Summary: Size to density coupling of supported metallic clusters
Elad Gross and Micha Asscher*
Received 4th June 2008, Accepted 24th October 2008
First published as an Advance Article on the web 26th November 2008
DOI: 10.1039/b809355e
One of the difficulties in standard growth of metallic nano-clusters on oxide substrates as model
catalysts is the strong coupling between clusters size and density. Employing multiple cycles,
amorphous solid water­buffer layer assisted growth (ASW-BLAG) procedure, we demonstrate
how the size to density coupling can be eliminated under certain conditions. In this study, gold
clusters were deposited on a SiO2/Si(100) substrate in UHV, using ASW as a buffer layer assisting
aggregation and growth. The clusters were imaged ex situ by tapping mode atomic force
microscope (AFM) and high-resolution scanning electron microscope (HR-SEM). In situ Auger
electron spectroscopy (AES) measurements have led to independent evaluation of the gold
covered area. In order to increase the clusters density we have introduced a multiple BLAG
procedure, in which, a BALG cycle is repeated up to 10 times. The cluster density can be
increased this way by more than five fold without changing their size. Above a specific number of
cycles, however, the cluster density reaches saturation and a gradual increase in clusters size is
observed. Larger clusters correlate with lower saturation density following multiple BLAG cycles.
This observation is explained in terms of long range cluster­cluster attraction between clusters
already on the substrate and those approaching in the next BLAG cycle. This attraction is more

Source: Asscher, Micha - Institute of Chemistry, Hebrew University of Jerusalem

Collections: Chemistry