HIGH-RESOLUTION ELECTRON-MICROSCOPE OBSERVATION OF MEDIUM-RANGE ATOMIC ORDERING IN AMORPHOUS ALLOY

Amorphous Pd82Si18 thin films were prepared by the argon-beam sputtering technique. The specimens were deposited on NaCl substrates with a substrate temperature of 293 K. An investigation of the medium-range order (MRO) and its relation to the structural relaxation and decomposition on annealing has been made by means of high-resolution electron microscopy, nano-beam diffraction and nano-beam elemental analysis. Domains of fcc MRO were observed in the as-sputtered film. At the initial stage of annealing, the number of observed MRO domains increases and they grow with increasing annealing temperature. This stage corresponds to that of structural relaxation. The large grown fcc MRO domains become nano-precipitates which may be called 'nuclei of the alpha-Pd precipitates'. The lattice parameter of the nano-precipitates becomes closer to that of pure alpha-Pd with increasing size of precipitates. The Si composition in the (nano-)precipitates starts to decrease when the annealing temperature is increased to 523 K.