Transmission electron microscopy and Monte Carlo simulations of ordering in Au-Cu clusters produced in a laser vaporization source - art. no. 165406

Au-Cu bimetallic alloy clusters are produced in a laser vaporization sourer starting from Au-Cu alloy targets with different stoichiometric compositio ns. The clusters are deposited on two different substrates-amorphous carbon and crystalline MgO-and are characterized by electron diffraction and high -resolution electron microscopy. The experiments show that the overall chem ical composition in the clusters is the same as the chemical composition of the target material; but the crystal structure of the Au-Cu alloy clusters differs from their known bulk crystal structure. Electron microscopy exper iments provide evidence that no chemical ordering exists between Au and Cu atoms and that the clusters an solid solutions. Monte Carlo simulations usi ng the second moment tight-binding approximation, however, predict Cu3Au cl usters ordered in the core but with a disordered mantle. The possible origi ns of the differences between experiment and Monte Carlo simulations are di scussed.