Colloidal Crystal Growth on Chirped Grating Surfaces

In this work, we report the lattice structures of monodisperse colloidal crystals grown on a chirped grating surface via confined convective self-assembly. The grating was fabricated by using a laser interference lithography technique. The periodicity of the substrate ranges from 660 nm to 11,000 nm. Employing a chirped grating allows for analysis of a large periodicity range on a single substrate. When the grating periodicity is much larger than the diameter of the colloidal particle, the grating simply served as a compartment for the particles which resulted in formation of chain-like structures. Conversely, when the periodicity of the grating is commensurate to the diameter of the particles, the gratings influenced the crystal lattice structure formed. The crystal lattice structure transitioned from a square lattice to a triangular lattice through a rhombic intermediate structure. The crystal structures were optically characterized by laser diffraction with a corresponding SEM image.We have also shown that the monolayer crystal lattices can serve as templates for growth of unique structures such as rectangular lattice, chains of particle pairs or triplets, graphite-structured lattice, etc.