Epitaxially grown colloidal crystals of silica microspheres on patterned substrate of triangular arrays

We have studied the colloidal self-assembly of silica microspheres on a glass substrate patterned with triangular dimple arrays of varying pitch. Using the same silica microspheres, both charge-stabilized and hard-sphere-like binary mixtures of microspheres and nanoparticles were prepared, and their gravitational sedimentation followed by colloidal crystallization were rigorously examined in real-space using a laser scanning confocal microscopy. In wet colloidal crystals, both systems showed a strong preference toward face centered cubic (fcc) stacking, the thermodynamically stable crystal form. After drying however, only the hard-sphere-like binary mixture of silica microspheres and zirconia nanoparticle maintained the initial templated fcc structure. The charge-stabilized system was disordered as the water was removed. Rigorous analysis of random defect structures such as stacking faults and vacancy concentration were carried out and discussed. Highly oriented colloidal crystals are of interest because of their potential use as templates for various applications.