  In directed assembly, small building clocks are assembled into an organized
structures under the influence of guiding fields. Capillary interactions
provide a versatile route for structure formation. Colloids adsorbed on fluid
interfaces distort the interface, which creates an associated energy field.
When neighboring distortions overlap, colloids interact to minimize interfacial
area. Contact line pinning, particle shape and surface chemistry play important
roles in structure formation. Interface curvature acts like an external field;
particles migrate and assemble in patterns dictated by curvature gradients. We
review basic analysis and recent findings in this rapidly evolving literature.
Understanding the roles of assembly is essential for tuning the mechanical,
physical, and optical properties of the structure.
