Deciphering NonCubic Phases in Au Microcrystallites via Under Potential Cu Deposition and Selective Growth of Noble Metal and Sulfide Overlayers

Identification of the crystal phase domain in a given crystallite requires high-resolution electron microscopy and selected area diffraction techniques. However, it is an immense challenge to prepare the samples and identify the polymorphic domains in a crystallite, specifically when the size of the domains is in the μm regime. Here, the well-known Cu electroless process has been used to map the fcc lattice domains from a group of mixed phases in Au crystallites. The Cu growth was selective on the fcc domains, while the noncubic lattice regions (i.e., body-centered orthorhombic and body-centered tetragonal, together called bc(o,t) lattices) remained free of Cu. In spite of the similar lattice mismatches, the Cu deposition is mainly governed by the isotropic geometry of the fcc surfaces, irrespective of the crystal morphology. The obtained Au–Cu structures have served as seeds to grow bimetals (Au–Ag, Au–Pd, and Au–Pt) and metal–semiconductors/heterostructures (Au–CuS and Au–Cu₂O) with anisotropic geometry.