Abstract
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{111}, 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.