Structure of sputter-deposited amorphous Pd-Si alloy studied by High Resolution Electron Microscopy

Abstract

Recent structural studies of amorphous alloys by precise X-ray and neutron diffraction, Mossbauer spectroscopy and NMR have shown an atomic ordering developing beyond the first neighbor atomic distance, which is called a medium range ordering (MRO) of atoms in amorphous alloys. Lattice fringe images extending in a range of 1 to 2 nm have been observed in amorphous alloys by high resolution electron microscopy(HREM), indicating a possible formation of the MRO structures. In our HREM study of amorphous Pd77.5Cu6Si16.5 alloy ribbons, MRO domains with α-Pd-like structure were observed under the most appropriate underfocus condition. For more detailed understanding of MRO structure, it is necessary to calculate HREM images for possible MRO models and compare them with observed ones. In this study, we calculated HREM images for an amorphous Pd80Si20 with (1) a dense random packing(DRP) structure, (2) a FCC MRO structure( a FCC cluster embedded in the DRP structure) and (3) an icosahedral MRO structure( an icosahedral cluster embedded in the DRP structure).