Template-directed growth of (100)-oriented colloidal crystals

This paper describes a simple and convenient procedure that allowed for the fabrication of large colloidal crystals with their (100) planes oriented parallel to the surfaces of supporting substrates. Such crystals were grown by templating against two-dimensional (2D) regular arrays of square pyramidal pits or V-shaped grooves etched in the surfaces of Si(100) substrates. The capability and feasibility of this approach have been demonstrated by crystallizing spherical colloids (> 250 nm in diameter) into (100)-oriented crystals over areas as large as several square centimeters. We further demonstrated that inverse opals with (100) crystallographic orientation could be fabricated by templating liquid precursors (such as a UV-curable prepolymer) against these colloidal crystals. In addition to silicon templates whose fabrication involved extensive use of cleanroom facilities, multiple copies of polymer templates having similar functions were also generated by replica molding, a process that could be performed in any ordinary laboratory. We believe that the ability to control the crystallographic orientation of colloidal crystals will greatly enrich our studies on their properties. In particular, the availability of large colloidal crystals with specific crystallographic orientations should allow us to systematically investigate their photonic band structures in an effort to elucidate their structure-property relationship.