Structure of mixed clusters formed in supersonic jets of Ar-N2 gas mixtures

An electron diffraction study is done on substrate-free clusters formed from nanodrops in expanding supersonic jets of Ar-N-2 gas mixtures. The mean characteristic linear dimension of the clusters varies from 20 to 200 A, and the temperature of the clusters is 40 K. The content of the gas mixtures spanned the entire concentration interval. These studies revealed that the mixed Ar-N-2 clusters are enriched with Ar, and a method for determining the absolute concentrations of the cluster constituents is proposed. The structure of the clusters in relation to their size and the component concentrations is established for the first time. The diagram of the structural states is compared with published data for bulk samples grown from the liquid. A transformation from the fcc to the hcp structure on increasing cluster size is revealed, and also a transformation from the hcp to an hcp+fcc structure with increasing argon concentration; this is not observed in the bulk samples. In clusters the mutual transformations of these structures occur without a change of the interatomic distances. (c) 2007 American Institute of Physics.