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Nanostructure Formation in a Vapor Phase

Nanostructure Formation in a Vapor Phase Using Heterogeneous Nucleation Sites

The vapor phase formation of nanostructures through self-assembly, directed-assembly or island growth modes has been studied for many years and has yielded a wide array of nanostructures. We, however, have devised a simple technique whereby periodic arrays of nanostructures are first formed using dynamic templating and are then treated as heterogeneous nucleation sites in subsequent assembly processes. In a typical processes, Au nanostructures are confined between an oxide substrate and a second material from which adatoms can be sourced through sublimation. At the assembly temperature these adatoms are unable to spontaneously form stable clusters on the substrate surface. When they encounter a Au template, however, they are readily incorporated to form a new nanostructure with its own unique properties. This strategy has been demonstrated for scenarios where Au in transformed into an alloy, where it forms a eutectic liquid which upon cooling phase separates into a heterodimer structure, where the Au template is sacrificed and replaced with a Wulff-shaped Pd nanostructure and where Wulff-shaped Au nanostructures are transformed into triangular AuAg nanoprisms.

Schematics_Au_template_to_AgAu_triangle

Schematic of the growth mode devised to form periodic arrays of AuAg nanoprisms.

SEM images of arrays of Au templates and AgAu triangles (top) and AgGe heterodimers and Ag nanocrescents (bottom).