Mechanically/thermally induced shape-morphing for atypical micro/nanostructures

Abstract

thus, they do not lend themselves to the fabrication of a variety of atypical micro/nanostructures. This thesis therefore proposes a parallel fabrication process for fabricating atypical 2D/3D micro/nanostructures (multilayer-, heterogeneous-, hierarchical-, three-dimensional structures). In addition, to improve the practicality by guaranteeing uniformity and reproducibility, the process is designed such that each of the micro-/nanoscale structures has an atypical shape but macroscopically, these structures are uniformly arrayed and controlled. The process was realized by drawing from methods inspired by techniques developed for macroscopic-scale fabrication during the evolution from 3D printing to 4D printing. The proposed methods are appropriate for fabricating atypical structures in that they include a secondary shape-morphing step involving the application of additional external thermal or mechanical stimuli to the 2D nanostructures fabricated by the conventional nanotransfer process. The thermally induced shape-morphing step of a polymer substrate or metallic thin film of multilayered or heterogeneous nanostructures is described in Chapter 2. The mechanically induced shape-morphing step of bound or suspended 2D nanostructures for hierarchical or 3D micro/nanostructures is described in Chapter 3. Finally, to demonstrate the broad applicability of the atypical micro/nanostructures, those fabricated using the developed process are incorporated in electronic devices with various applications such as surface-enhanced Raman spectroscopy (SERS) for the detection of biomolecules, security patterns for anti-counterfeiting, a superhydrophobic triboelectric nanogenerator (S-TENG) for the self-powered detection of coughing, and a stretchable gas sensor for the detection of explosive/toxic gases.

Complex two-dimensional/three-dimensional (2D/3D) atypical micro/nanostructures are being widely used in various fields such as physical/chemical sensors, energy harvesting, security patterns, and optical devices. Accordingly, research on the fabrication processes of the various atypical micro/nanostructures is also being actively conducted. The methods that have been developed thus far to fabricate atypical structures can be categorized into two groups: serial and parallel processes. In general, serial processes require complex equipment and have a low throughput, whereas parallel processes have limited design diversity. In addition, materials that are compatible with each of these groups of processes are limited owing to their respective procedures. Moreover, they were designed to fabricate standardized structures (i.e., lines, holes, and pillars)