Gold colloids with unconventional angled shapes.

We report the formation of porous gold nanoparticles with unusual, angled shapes (such as nanocheckmarks) through spontaneous transformation of tellurium sacrificial templates by gradual galvanic replacement. High-resolution electron microscopy studies of intermediate stages reveal interesting information regarding the replacement mechanism, which involves initial "gold island growth" at the edges, and gradual branching to engulf the entire particle templates, resulting in a highly porous structure. Additionally, the high porosity of these novel nanostructures with unusual shapes is demonstrated to provide very high enhancement of the Raman scattering signal from adsorbed molecules.