Growth imperfections in three-dimensional colloidal self-assembly

Self-assembled colloidal films produced from vertical deposition often show alternating bands of arrayed spheres and empty regions on the substrate as the solvent evaporates. We have identified three distinct growth zones, their relative extent being a function of colloidal concentration. We attribute the growth pattern to a 'stick-slip' motion of the meniscus growth front, a direct consequence of the dynamic balance of surface-tension forces and the convective transport of nanoparticles. Within these zones, the crystalline quality of the colloidal crystals is dependent on the wetting characteristics of the meniscus. These colloidal crystals also exhibit cracks of different morphologies within the different growth zones as a result of the drying process. We deduce that these macroscopic imperfections may be reduced by improving substrate wettability and reducing evaporation rate.