Dislocations in gold as an “autocatalytic template” for nanowire growth

Technion researchers have presented an innovative method for the formation of nanowires. In it, the nanowires form within line defects that exist in metals. Such defects are known as dislocations. This is the first time that dislocation lines in a material of one kind serve as a template for the growth of a different inorganic material in the form of nanowires. The study, which was published in PNAS, was led by Professor Boaz Pokroy and Ph.D. student Lotan Portal of the Faculty of Materials Science and Engineering and the Russell Berrie Nanotechnology Institute.

Dislocations are a significant phenomenon in materials science since they affect the material’s properties on both the macro- and microscales. For example, a high dislocation density increases a metal’s strength and hardness. The dislocation edges on metal surfaces and the atoms in their proximity tend to be more chemically activated compared to other atoms in the material and tend to facilitate various chemical reactions, such as corrosion and catalysis.

The researchers in Prof. Pokroy’s group created nanowires of gold-cyanide complex from classic Au-Ag alloy. In professional terminology, they synthesized inorganic gold(I)-cyanide (AuCN) systems in the shape of nanowires, using an autocatalytic reaction (i.e. through the acceleration of a reaction by one of its reactants). Gold-cyanide complex is used in numerous fields including ammonia gas detection (NH₃ sensors), catalysis (acceleration) of water-splitting reactions, and others.

In the process developed by the researchers, nanowires crystallize at the dislocation ends on the surface of the original gold-silver (Au-Ag) alloy, and the final structure obtained is classic nanoporous (sponge-like) gold, with a layer of nanowires emerging from it. Formation of the nanowires occurs during the classic selective dealloying process that separates the silver from the system and forms the nanoporous gold and is achieved only when the dislocation density exceeds a critical value, as presented in the kinetic model developed and demonstrated in the article.

The model provides a possible route for growing one-dimensional inorganic complexes while controlling the growth direction, shape, and morphology of a crystal according to the original alloy’s slip system. As mentioned, this scientific and technological achievement has numerous potential applications.

The research was sponsored by a European Research Council (ERC) Proof of Concept Grant (“np-Gold” project) as part of the Horizon 2020 Program.