Formation of Non-equilibrium Alloys Through Nanocluster Deposition: The Ag_0.3Al_0.7 Supersaturated Alloy

We present here results of soft landing 4 nm sized clusters of Ag from a nanocluster beam on Al for 5 mins and 15 mins. We have studied the samples after cluster deposition using X-ray Photoelectron Spectroscopy, Secondary Ion Mass Spectroscopy, and X-ray Diffraction. We have found that no Ag nanoparticles have formed, the Ag is not oxidised but the Al has undergone some hydrated oxidation. More important, we have established the formation of the supersaturated Ag_0.3Al_0.7 alloy with an fcc structure at ambient temperature and at Ag concentrations ∼ 0.1%-0.2% of the total atoms in the sample, for both the 5 min and 15 min irradiated samples, growing with the same orientation as the Al lattice, with traces of another phase suggestive of the hcp phase of Ag₂Al. Interestingly, the crystallinity of the alloy in both cases is better than that of the Al lattice and they have a marginally lower strain. We have proposed an explanation of the strong tendency to form Ag-rich alloys by invoking a recently established structure of Al with very low bonding electron density localised at the tetrahedral interstices. (paper)