Facet selective etching of Au microcrystallites

Abstract

High-symmetry crystals exhibit isotropic properties. Inducing anisotropy, e.g., by facet selective etching, is considered implausible in face-centered cubic (FCC) metals, particularly gold, which, in addition to being an FCC, is noble. We report for the first time the facet selective etching of Au microcrystals obtained in the form of cuboctahedra and pentagonal rods from the thermolysis of a goldorganic precursor. The selective etching of {111} and {100} facets was achieved using a capping method in which tetraoctylammonium cations selectively cap the {111} facets while Br^– ions protect the {100} facets. The exposed facets are oxidized by O₂/Cl^–, yielding a variety of interesting geometries. The facet selective etching of the Au microcrystallites is governed only by the nature of the facets; the geometry of the microcystallite does not appear to play a significant role. The etched surfaces appear rough, but a closer examination reveals well-defined corrugations that are indexable to high hkl values. Such surfaces exhibit enhanced Raman activity.