Colloidal Diamond Crystals

Self-assembling colloidal diamond has been a longstanding goal because of the structure's potential for photonic applications. Because particles in a diamond lattice are tetrahedrally coordinated, one approach has been to self-assemble spherical particles with tetrahedral sticky patches. Difficulties persist, however, because the patchy particles possess no mechanism to select the proper staggered orientation of tetrahedral bonds on nearest-neighbor particles, a necessary requirement for cubic diamond. Here, we show that by using partially compressed clusters with retracted sticky patches, colloidal cubic diamond can be self-assembled using patch-patch adhesion together with a steric interlock mechanism that selects the proper staggered bond orientation. Colloidal particles in the self-assembled diamond structure are highly constrained and mechanically stable, which makes it possible to dry the suspension and retain the diamond structure. The inverse lattice exhibits promising photonic properties, including a complete photonic bandgap.