'The Graduate School of the Humanities, Utrecht University'
Abstract
We demonstrate that randomly stacked hard-sphere colloidal crystals do not
merely consist of random sequences of hexagonally close-packed layers, but
also of islands within the hexagonal layers with different lateral positions A,
B and C. The existence of such in-plane stacking disorder was suggested by a
recent observation of lateral broadening of the Bragg scattering rods in micro
radian X-ray diffraction and is further confirmed here by real-space confocal
microscopy in two hard-sphere colloidal systems with different sedimentation
Peclet numbers. The transition from one lateral position to the other either
occurs discontinuously through line-defects or continuously in a bridging area
through a lattice deformation and results in transitions between hexagonally
close packed and face centered cubic structures. The subsequent chapter is
dedicated to the continuous transitions. In this chapter the discontinuous linedefects
are characterized, up to their 3-D structure. The chance ζ to find
another line-defect above a line-defect in the layer below turns out to be close
to 1/2 – independent of relative gravity – which can be explained by the two
different stacking options above a defect. The stacking of a few sets of several
line-defects situated on top of each other turns out to be predominantly FCClike
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