Clusters of gold atoms forming a strange pyramid shape, Clusters consisting of several atoms are usually spherical in shape. They are usually arranged in atomic shells around a central atom.
This applies to many elements, but not to gold. Sophisticated experiments and calculations have shown that free-standing clusters of twenty gold atoms take the form of a pyramid.
They have a triangular base plane, consisting of ten neatly arranged atoms, with an additional triangle of six and three atoms, which are crowned by one atom.
The extraordinary tetrahedral structure is now shown for the first time with a scanning tunneling microscope. With this high-tech microscope, individual atoms can be made visible. It works at very low temperatures (269 degrees below zero) and uses quantum tunneling electric current from the sharp metal scanning tip through the cluster to the carrier.
Quantum tunneling is the process by which an electric current flows between two wires without physical contact between them.
The researchers used intense plasma in an advanced vacuum chamber to disperse gold atoms from a macroscopic piece of gold. “Some scattered atoms grow together and form small particles with several to several dozen atoms, which are proportional to the condensation of water molecules into droplets,” the researchers said.
We selected a bundle of clusters consisting of exactly twenty gold atoms. We landed this species with one of the triangular coatings on the substrate covered with a very thin layer of salt (NaCl) which was exactly as thick as three layers of atoms.
The study also revealed the special electronic structure of a small golden pyramid. Like noble gas atoms or aromatic molecules, these clusters only have full electron orbitals, which makes them far more reactive than clusters with one or more or more atoms.
Gold clusters with several to several dozen atoms are known to have extraordinary properties. This new finding helps scientists to assess the catalytic and optical properties of this cluster, which are important for the design of cluster-based catalysts and optical devices.
Recent cluster applications include use in fuel cells and carbon capture.