Growth and Defect Structure of Lamellar Gold Microcrystals

A common nonequilibrium form exhibited by gold microcrystals grown from solution is a thin (111) platelet of trigonal or hexagonal symmetry. From moiré patterns it has been established that these crystals are essentially free of dislocations if the growth temperature is kept constant. Using both bright‐ and dark‐field electron microscopy and electron diffraction at various crystal orientations it has been shown that the major imperfection is coherent twinning in the large (111) planes of the crystals. The layered growth can be explained on the basis of a twin‐accelerated growth mechanism involving multiple twinning on parallel (111) planes. Anomalous ED spots of the type ⅓$\text{{4̄22}}$ can be explained on the basis of a nonzero structure facture resulting from a stacking disorder in the (111) planes. An electron microscopic and diffraction study of various stages of growth indicates that multiple twinning occurs very early in the growth process. An intermediate structure is exhibited by the gold platelets during the initial 40% of the growth process. It is speculated that the intermediate phase involves a gold compound of the type Au₂X.