In situ observation of alloying behavior in metal atom clusters has been carried out with a 200kv transmission electron microscope equipped with a double-source evaporator in the specimen chamber. With the use of the evaporator isolated gold clusters of 3 nm in size were first prepared on a supporting film of amorphous carbon, and copper atoms were then deposited onto the same film. Upon the deposition of copper, the gold clusters quickly changed into highly concentrated, homogeneously mixed Au-Cu alloy clusters. This spontaneous alloying has taken place without visible translational motion of individual clusters on the supporting film. The copper atom diffusivity in the clusters observed here is approximately 9 orders of magnitude faster than that in bulk crystalline alloys.
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Yasuda et al. (1992) studied this question.