An experimental and theoretical investigation of the anisotropic branching in gold nanocrosses

In this work, copper (Cu) species were used as reducing reagents in the colloidal preparation of novel cross-shaped gold (Au) nanostructures in oleylamine. The reduction rate can be controlled through an appropriate choice of Cu species to obtain Au nanocrosses of varying sizes. It was found that the presence of Cu species during the nucleation stage is crucial to the formation of a branched morphology. Further analysis revealed that the four primary branches of the Au nanocrosses grow along the < 110 > and < 001 > directions, and that secondary branched growth occurs along the < 111 > direction. First-principles calculations and phase-field models were used to rationalize the observed preferential branching and understand the morphological evolution of the nanocrosses. These unique cross-like Au nanostructures exhibit strong NIR absorption and remarkable plasmonic properties that make them promising materials for optical and biomedical applications.