  Active colloids self-organise to a variety of collective states, ranging from
highly motile 'molecules' to complex 3D structures. Using large-scale
simulations, we show that hydrodynamic interactions, together with a
gravity-like aligning field, lead to tunable self-assembly of active colloidal
spheres near a surface. The observed structures depend on the hydrodynamic
characteristics: particles driven at the front, pullers, form small chiral
spinners consisting of two or three particles, whereas those driven at the
rear, pushers, assemble to large dynamic aggregates. The rotational motion of
the puller spinners, arises from spontaneous breaking of the internal
chirality. Our results show that the fluid flow mediates chiral transfer
between neighboring spinners. Finally we show that the chirality of the
individual spinners controls the topology of the self-assembly in solution:
homochiral samples assemble into a hexagonally symmetric 2D crystal lattice
while racemic mixtures show reduced hexatic order with diffusion-like dynamics.
