(164a) Controlling Colloidal Crystal Growth Using Surface Relief Patterns

The ability of colloidal materials to self-assemble into ordered structures with unique properties has created considerable interest in their application in the fields of optics and photonics. One of the most attractive properties of nanometer and micron-sized particles is their tendency to form crystalline assemblies, which makes them a versatile building block for the fabrication of colloidal crystals. These materials exhibit interesting optical properties, including photonic bandgaps, which are strongly influenced by their underlying periodic crystal structure. Control of the assembly of the colloidal crystals is essential to tailor their resulting properties. The use of templates to guide the assembly and growth of the colloidal crystals allows for creation of structures different from those found via natural self-assembly. These photonic band gap materials or photonic crystals have found application in optical filters, sensors, and waveguides.

In this work, we report the use of complex surface relief patterns as templates in a convective self-assembly colloidal deposition method to guide the growth of colloidal crystal lattices and produce highly ordered monolayer arrays. A variety of complex template structures, including two-dimensional (2-D) chirped gratings and a series of quasicrystal and Moiré lattices are explored to analyze their effects on templating different colloidal crystal lattices. We analyze the impact of the pitch value and the symmetry of the templates on the various colloidal crystal lattices using optical microscopy and optical diffraction. We determine that in a 2-D chirped grating, pitch values have a large influence on how the colloids assemble, forming structures ranging from chain-like to square and rectangular lattices. In more complex templates, the colloidal assembly is greatly influenced by the template structure, resulting in lattices with high rotational symmetries. We demonstrate that by varying the grating template structure, a wide range of lattice configurations can be created. We anticipate the crystal lattices introduced in this work can be used as building blocks to form 3D photonic crystals in optical band-gap applications and the results here presented can be further extended by employing different sized particles to form binary colloidal crystals.