Spontaneous alloying of copper into gold atom clusters

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Abstract
A double-source evaporator which can be set in the specimen chamber of a high voltage electron microscope has been constructed, With the use of the evaporator, isolated gold clusters of 5 ~ 10 nm in size were first prepared on a supporting film of amorphous carbon, and then copper atoms were deposited onto the film (and of course onto the gold clusters as well), which was kept at room temperature. Upon the deposition of copper, the gold clusters changed into highly concentrated, homogeneously mixed Au—Cu alloy clusters. The copper atom diffusivity in gold clusters deduced from the present observations is at least 9 orders of magnitude faster than the copper solute diffusion in bulk gold.