  For low to moderate supersaturations, crystals grow by lateral build-up of
new layers. The edges of the layers are known as "steps". We consider the rate
of step advance on a flat crystal face under the influence of bulk diffusion in
the complete absence of advection, assuming a steady-state. In such
circumstances, the step velocity tends asymptotically to zero as the radius of
curvature increases. This counters the Gibbs-Thomson effect according to which
the rate of step advance should asymptotically increase \textit{ceteris
paribus} with increasing radius of curvature. Because of these competing
effects, the rate of step advance is expected to be non-monotonous in the
radius of curvature.
