  The phase diagram of Yukawa particles confined between two parallel hard
walls is calculated at zero-temperature beyond the bilayer regime by
lattice-sum-minimization. Tuning the screening, a rich phase behavior is found
in the regime bounded by stable two-triangular layers and 3-square layers. In
this regime, alternating prism phases with square and triangular basis,
structures derived from a hcp bulk lattice, and a structure with two outer
layers and two inner staggered rectangular layers, reminiscent of a Belgian
waffle iron, are stable. These structures are verifiable in experiments on
charged colloidal suspensions and dusty plasma sheets.
