Self-Assembly of Three-Dimensional Curved Micro- and Nanostructures: From Horizontal to Vertical Alignment

Abstract

Stunning majestic architecture with elegant curvature on a macroscale has been built around the world for centuries. However, constructing microscale architectures that curve out of planes is tough due to a significant incompatibility between conventional two-dimensional (2D) planar lithography techniques and three-dimensional (3D) micro curvature. Especially, fabricating high aspect ratio, vertically-aligned curved microstructures decorated with versatile materials on their surfaces (reminiscent of architectural forms but at the microscale), is particularly challenging, and cannot be achieved with current 3D printing techniques. The Origami-like self-assembly approach, with a bottom-up feature that curves the pre-designed 2D patterns out of plane, is very promising to address these obstacles. My Ph.D. work involves developing new self-assembly approaches to fabricate high aspect ratio, vertically-aligned curved microstructures with materials patterning. Such a complex microsystem is unable to be realized by one-directional self-assembly techniques. Therefore, a dual directional self-assembly approach is invented in this thesis. This thesis can be roughly divided into two parts. The first part focuses on building 3D curved circular nanotubes in the xy-plane using electron beam induced self-assembly. Through a simple one-directional self-curving process, this work is believed to be the first successful fabrication of curved circular nanofluidic channels with capability of nanofluid transport. This achievement, accomplished by only one-directional self-assembly, highlights the significant potential to construct multi-directional self-assembly of curved 3D micro- and nanostructures with high complexity. Therefore, the second part of the thesis is the most critical, focusing on the development of a dual-directional self-assembly process to achieve vertically-aligned monolayer graphene micro helices. The first self-assembly direction concentrates on helix self-twisting within the xy-plane, while the second direction focuses on self-folding the entire graphene helical structure out of plane (from xy-plane to z-direction) until vertical direction. Especially, the research on how to shape the helix vertically with precise control is strongly emphasized. This self-assembly mechanism is pioneering and to the best of my knowledge, it has not been reported elsewhere. Therefore, the underlying mechanism is also thoroughly investigated in this thesis. This dual-directional self-assembly approach holds significant promise for advancing innovative research and enabling diverse applications across fields.