INVESTIGATION OF THE ATOMIC-STRUCTURE AND VISIBILITY OF CRYSTAL AMORPHOUS INTERFACES IN PD80SI20 ALLOY BY HRTEM IMAGE SIMULATIONS

Atomic models of isolated crystalline Pd3Si embedded in amorphous Pd80Si20, a planar crystalline Pd3Si/amorphous Pd80Si20 interface and a faceted crystalline Pd3Si/amorphous Pd80Si20 interface were constructed using a dense random packing (DRP) model for the amorphous alloy. Multislice programs were used to simulate high-resolution transmission electron microscope (HRTEM) images of these models for a JEOL 4000EX microscope. The simulated images show that amorphous alloy superimposed on crystalline Pd3Si degrades the crystal image. The visibility limit of crystalline Pd3Si embedded in amorphous Pd80Si20 occurs for an amorphous/crystal thickness ratio of about 3.4 near optimum defocus (-50.0 nm), but this can be increased by a factor of two using optical diffraction. A similar visibility limit occurs for crystalline protrusions at a crystal/amorphous interface. The visibility limit is affected by defocus, and at -60.0 nm defocus a crystalline protrusion of Pd3Si can become more visible due to a zero in the microscope contrast transfer function at the nearest-neighbor bond distance of the amorphous alloy. The atomic arrangement of crystalline Pd3Si extends a few atomic diameters into the amorphous matrix for a crystal/amorphous interface constructed with the DRP model, and this structure can be observed by HRTEM.