Electron diffraction and high-resolution electron microscopy study of an amorphous Pd82Si18 alloy with nanoscale phase separation -: art. no. 094201

A structure model of nanoscale phase separation has been proposed for a structure of an amorphous Pd-Si alloy with the eutectic composition on the basis of electron diffraction and high-resolution electron microscopy (HREM). A sputter-deposited amorphous Pd82Si18 alloy film with a thickness of about 10 nm was specially used in order to minimize the effect of multiple scattering. A local atomic ordering with sizes of 1-2 nm was observed by HREM, similar to that observed in liquid-quenched ribbon specimens. From HREM images and nanodiffraction analysis, the atomic structure of the ordering regions was determined to be of the fcc-Pd type. Atomic pair distribution function (PDF) analysis for the thin-film alloy was performed by precise measurement of haloelectron-diffraction intensity using the imaging-plate technique. In the diffraction intensity analysis, the inelastic part of intensity was removed by an intensity correction using electron energy-loss spectroscopy. In order to explain the results of HREM, nanodiffraction, and PDF studies comprehensively, a nanoscale phase-separation structure model has been constructed with the help of reverse Monte Carlo calculation. A structure model with fcc-cluster regions embedded in a dense-random-packing structure of Pd and Si was finally obtained. The model proposed here is thought to be typical for amorphous alloys with near-eutectic compositions cooled under limited cooling rates.