Nano-alloys synthesized by controlled crystallization from supercooled atomic clusters of elements

Abstract

Materials in nanocrystalline forms are well known to possess unusual and interesting properties when compared to the bulk conditions, and these open up an exciting range of novel applications. The key step involved in the systematic exploitation of nanocrystals for real applications lies in the development of reliable methods to synthesize nanocrystals of arbitrary chemical compositions in a range of crystal sizes. In particular, metallic alloy nanocrystals pose a special challenge. We demonstrate that nano-to-micro-sized crystals of intermetallic nickel-aluminide (Ni3Al) ranging from approximately 3 nm to over 100 nm in size can be synthesized by co-sputtering from elemental Ni and Al onto unheated, incompatible organic substrates, followed by controlled postdeposition heat treatment at mild temperatures. The crystal size of approximately 3 nm here is the smallest ever reported for monolithic ordered Ni3Al.