  Less-defective colloidal crystals can be used as photonic crystals. To this
end, colloidal epitaxy was proposed in 1997 as a method to reduce the stacking
defects in the colloidal crystals. In this method, face-centered cubic (fcc)
(001) stacking is forced by a template. In fcc (001) stacking, in contract to
fcc {111} stacking, the stacking sequence is unique and thus the stacking fault
can be avoided. Additionally, in 1997, an effect of gravity that reduces the
stacking disorder in hard-sphere (HS) colloidal crystals was found. Recently,
we have proposed a gravitational tempering method based on a result of Monte
Carlo (MC) simulations using the HS model; after a colloidal crystal is grown
in a relatively strong gravitational field, the defects can be reduced by
decreasing the gravity strength and maintain for a period of time. Here, we
demonstrate this method using MC simulations with a programed gravitation. The
dramatic disappearance of defect structures is observed. Gravitational
tempering can complement gravitational annealing; some defect structures that
accidentally remain after gravitational annealing (keeping the colloidal
crystal under gravity of a considerable constant strength) can be erased.
