Interlacing of
growth steps on crystal surfaces as a consequence of crystallographic
symmetry
W. J. P. van Enckevort and P. Bennemaa
Acta Cryst. A60
(2004) 532-541
Abstract:
During crystal growth, concentric steps of unit-layer thickness
[= , with the surface's hkl Miller indices corrected according to the
selection rules for non-primitive lattices] are often found to split
into lower steps in a regular fashion [Frank (1951). Phil. Mag. 42,
1014-1021]. These `interlaced' step patterns are introduced by a
stacking of two or more growth layers, with different lateral
anisotropy in step velocity within each unit layer. In this paper, a
general relation between the symmetry of the crystal surface and the
configuration of the concentric step patterns thereon is derived and is
used to give theoretical shapes of spirals, growth hillocks and etch
pits. It is shown that many of the interlaced patterns and their
details are imposed by the presence of screw axes and/or glide planes
perpendicular to the crystal surface. Finally, the results are compared
with the patterns of unit-layer height and lower steps observed by
optical and atomic force microscopy on crystals such as SiC, GaN,
potash alum, garnet and NiSO4·6H2O.