Surprising insights on metallic clusters

Victoria Wilton is a guest web-writer for PCCP. She is currently studying for a PhD at the University of Nottingham, UK.

Table of contents imageBetween bulk metals and their individual atoms lies the murky world of metallic clusters. These often have unique properties, and understanding them is as challenging as it is interesting. Many properties are a direct function of cluster size, and provide important insights into the progression from individual atoms to bulk solids. It is therefore important to ascertain the exact size at which a particle ceases to be classified as a cluster and becomes a bulk solid. This moment can either be measured experimentally or calculated using a theoretical model.

Aluminium bridges the gap between monovalent and multivalent clusters, as it is monovalent as a single atom, but becomes trivalent with hybridized orbitals at larger cluster sizes. The exact cluster size at which this hybridisation occurs is still the matter of intense debate, with little coherence amongst the results of a large number of studies, both experimental and theoretical.

Melko and Castleman attempt to resolve this problem by conducting both a theoretical study and an experimental study using the angular distribution information obtained from photoelectron imaging. They then developed a calibration curve that allowed them to quantitatively compare their results, which were rather surprising. They suggest that the orbital hybridisation that indicates bulk behaviour begins to appear at cluster sizes as small as Al3, which is considerably smaller than previously thought. The extent of the hybridisation then appears to oscillate as successive atoms are added to the cluster up to at least Al6, suggesting the existence of a transition period between the monovalent and trivalent states, rather than a discrete threshold.

by Victoria Wilton

Read the full details of this fascinating PCCP article:

Photoelectron imaging of small aluminum clusters: quantifying s–p hybridization
Joshua J. Melko and A. W. Castleman
DOI: 10.1039/C3CP43158D

If you enjoyed this paper you may also be interested in the Nanoscale themed issue on Metallic clusters – please do take a look.

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