Fabrication of high quality periodic structures through convective assembly procedures

Abstract

Techniques aimed at scalable realization of periodic structures from self-assembly of constituent building blocks, an approach that could supplant microfabrication procedures, are often constrained by the lack of diversity in packing arrangements achievable with assembly of simple constituents (e.g., spherical particles). In this work, we present a strategy to effectively pattern colloidal crystalline assemblies at two characteristic scales; achieving extensive non-classical particle packing amidst fully periodic, banded structural defects. We first introduce a scalable and robust approach to fabricate non-hexagonal crystals comprised of mono-sized spherical particles through introduction of periodically oscillating flow-fields during convective particle deposition. Through this technique, we report the discovery of extensive and tunable square-packed arrangements of monosized particles i.e., (100) fcc facets oriented parallel to the underlying substrate in self-assembled colloidal structures. Besides forming large (100) fcc crystalline domains with relatively few defects, the process also results in colloidal crystals having negligible variation in thickness while simultaneously yielding controlled proportions of both hexagonal and square-packed arrangements. The formation of domains of (100) fcc symmetry structures as a result of added vibration is robust across a range of micron-scale monosized spherical colloidal suspensions (e.g., polystyrene, silica) as well as substrate surface chemistries (e.g., hydrophobic, hydrophilic). In-situ visualization during self-assembly process as well as colloidal-crystal fabrication realized at varying frequency and amplitudes of vibration gives clues toward the mechanism of this flow-driven self-assembly method.In the second part of the work, we explore the introduction of volume defects in the uniformly-packed particle assemblies. Here, unlike randomly generated defects in packing structures, we demonstrate the formation of continuous, periodic banded defects comprised of particles with an fcc (110) packing configuration, and with tunable band periodicity. Studies aimed at discerning the specific effects of vibration conditions and meniscus properties help establish a mechanistic picture of the formation of fcc (110) banded structures based on stress relaxation in crystals through generation and movement of dislocations. The final chapters of the dissertation discuss how the convective assembly techniques could be efficiently used towards fabricating various devices for energy conversion and storage