Spontaneous alloying of copper atoms into gold clusters at reduced temperatures

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Abstract
The alloying behavior of copper atoms into gold clusters at temperatures lower than 300 K was examined using a 200 kV transmission electron microscope equipped with a double source evaporator in the specimen chamber. Isolated gold clusters of about 4 nm in mean diameter were prepared on a supporting film and were cooled down to 245, 215, 165, or 125 K. Copper atoms were then deposited onto the same film. Upon the deposition of copper, the gold clusters quickly changed into completely or partially alloyed clusters, depending upon the substrate temperature. The copper diffusivity estimated from such spontaneous alloying was many orders of magnitude faster than that in bulk gold. A possible mechanism behind the spontaneous alloying is discussed.