Abstract:
The (011) surface of the naphthalene crystal structure is described
by a simple restricted solid-on-solid model that Is applicable to a wide
range
of organic crystals. Despite the absence of next-nearest-neighbor bonds.
the phase diagram of the model exhibits, besides flat and rough phases,
a
disordered flat phase. Monte Carlo simulations confirm this phase diagram.
The presence of a disordered hat phase explains the sudden
disappearance of the (011) facet in experimental growth shapes of naphthalene.
The type of step-free energy associated with surface tilt decreases
rapidly, at preroughening transitions. This leads to a rapid decrease
in the nucleation barrier, which results in a sudden enhanced growth rate
and,
under certain conditions, to the complete disappearance of this facet
in growth shapes.