Surface-Sandwich Segregation Phenomena in Bimetallic Ag-Ni and Pd-Ni Nanoparticles: A Molecular Dynamics Study

By molecular dynamics simulation it is shown that interdiffusion in the initial f.c.c. Ag-core ( 28 at. %) – Ni-shell ( 72 at. %) and Ni-core ( 34 at. %) – Pd-shell ( 66 at. %) nanoparticles can lead to surface–sandwich segregation. It is observed that there is a separation of the initial Ag-Ni core-shell structure into Ag-core – Ni-intermediate shell – Ag-disperse surface monolayer. The initial crystal Ni-Pd core-shell structure transforms to the core of a non-crystalline Pd-rich solid solution with quite strongly developed icosahedral short-range order, which is covered by a surface–sandwich shell, where Ni atoms are located in the centres of interpenetrating icosahedra of a subsurface Kagomé net layer while the Pd atoms occupy the vertices of the icosahedra and cover this Ni layer from inside and outside. We demonstrate that under certain conditions a surface–sandwich segregation phenomenon at the nanoscale can be observed in systems with completely different phase diagrams in the bulk states: in systems displaying the extremely low mutual solubility as in the Ag-Ni system, or in systems exhibiting a continuous mutual solid solubility like the Pd-Ni system.

Phase Equilibria in Copper(I) Bromide-MBr Systems (M = Li, Na, K)

The phase equilibria of CuBr-LiBr, CuBr-NaBr and CuBr-KBr were studied by difference scanning calorimetry (DSC) and X-ray powder diffraction. Extended solid solutions have been found in CuBr-LiBr, while mutual solid solubility of the components of CuBr-NaBr and CuBr-KBr seems to be negligible. It has been confirmed that K2CuBr3 is stable at room temperature.

Epitaxy and diffusion-induced recrystallization in gold/copper films

Most previous studies of epitaxy have shown that growth of fee thin films on fee substrates leads to parallel, cube-on-cube orientation relationships. However, recent studies of Ag/Ni interfaces indicated that non-parallel orientation relationships may be preferred in fcc/fcc systems of large misfit. One objective of this study is to investigate the orientation relationships produced by epitaxy in Au/Cu bilayers. The Au/Cu system is especially interesting because it has complete mutual solid solubility despite the large lattice parameter misfit (∼ 12%). Hence, the second objective of this study is to investigate low-temperature interfacial diffusion phenomena in the special microstructures produced by multivariant epitaxy.