Growth and characteristics of the {1 1 1} NaCl crystal surface grown from solution

The morphology of {1 1 1} faces grown from water–formamide solutions as well as from pure water solutions was investigated. Surface patterns were examined ex situ and in situ using bright field and differential interference contrast optical microscopy and ex situ atomic force microscopy. It was shown that formamide and urea stabilize the {1 1 1} NaCl faces, whereas larger homologous molecules do not. For the {1 1 1} NaCl crystals growing from water–formamide solutions, it was observed that growth proceeds by monomolecular, stabilized layers of height d{1 1 1}, with most probably Na+ ions on top of Cl− ions. Steps originate from spiral-dislocation growth as well as from 2D nucleation starting from the edges of the crystal. Atomic resolution imaging of NaCl {1 1 1} showed no surface reconstruction. The {1 1 1} surfaces grown from pure water solutions showed developing of shallow growth hillocks with rounded tops. It is presumed that these hillocks are related to dislocation outcrops and growth proceeds close to the roughening temperature. Growth pits develop after a longer period of {1 1 1} surface growth in water solution. Their formation is explained by the presence of a semipermeable particle at the pit bottom, which locally retards the fast {1 1 1} growth.