Nanoalloys of Metals Which Do Not Form Bulk Alloys: The Case of Ag-Co

Ag and Co metals do not form macroscopic solid or liquid alloys. However, Ag_mCo_n clusters have been produced in dual-target dual-laser vaporization experiments, and the same occurs for other pairs of immiscible metals. We have performed density functional calculations to shed light on this phenomenon. The main result, obtained for clusters with sizes m + n not larger than 11, is that the cohesive energies justify that those clusters can be formed starting from free Ag and Co atoms, which is the case in the vaporization experiments. At the same time, mixing of Ag and Co is difficult even at the nanoscale. This is revealed by the application of several miscibility criteria. Those two features become, nevertheless, compatible in the clusters. Even if the cluster sizes considered are small, the emerging trend becomes clear: Co atoms form a core in the inner part, surrounded by a shell of Ag atoms on the surface. A consequence is that core-shell clusters can be formed from pairs of metals that do not form macroscopic alloys. The magnetic moments μ of the Ag_mCo_n clusters are due mainly to the Co atoms, and the presence of Ag induces a reduction in the magnitude of μ.

A microscopic level insight into Pt doped TiZn (001) surface for hydrogen energy storage usage

H-storage behavior on TiZn and Pt-doped TiZn alloys.

New Two-Dimensional Materials Obtained by Functionalization of Boron Graphdiyne Layers with Nickel

The decoration of hexagonal boron graphdiyne (BGDY) layers with Ni atoms has been investigated by density functional calculations. For one, two, and three Ni atoms per hexagon, the BGDY structure is approximately maintained. Decoration with six Ni atoms per hexagon leads to the formation of a novel, very stable two-dimensional material in which the hexagonal structure of BGDY is substantially distorted. The Ni-doped materials have a semiconductor character, and the electronic band gap width can be tailored by varying the amount of adsorbed Ni. BGDY-2Ni, BGDY-3Ni, and BGDY-6Ni have electronic band gaps promising for infrared detectors. This work shows that computer simulation helps to discover new materials by the functionalization of layered carbon materials with metal atoms.