DEVELOPMENT OF A RAPID, CONTINUOUS 3D NANOPRINTING SYSTEM BASED ON MULTIPHOTON ABSORPTION
Creators: name: Somers, Paul
Publisher: name: Purdue University Graduate School
Year: 2022
Subjects: Nanomanufacturing

description: 3D printing has established itself as a critical tool for manufacturing in all areas. It has evolved from a purely rapid prototyping technique into a feasible process for large-scale processing. A wide variety of 3D printing processes exist across an extreme range of size, from meters to nanometers. Much of the current technological advances come from pushing fabrication techniques to smaller and smaller scales. For 3D printing this has led to the rise of two-photon polymerization, a direct laser writing process with submicron structuring capabilities. Two-photon polymerization has proven its worth as a nanoscale 3D fabrication technique but is often considered slow and expensive, two undesirable qualities for high throughput manufacturing. Parallelization methods such as projection lithography are potential solutions to increasing the throughput capabilities of two-photon polymerization 3D printing. Additionally, the drive for further reducing the print size has inspired printing resolution enhancing strategies in two-photon polymerization printing by processes such as stimulated emission depletion (STED) and other STED-inspired pathways. This work will explore avenues for improving two-photon polymerization printing throughput and resolution. First, a two-photon polymerization printing system is constructed with a secondary laser for controlling polymerization inhibition. Through a STED process, a 65 nm wide printed line feature was achieved. Alongside this, a characterization and verification methodology for choosing new photoinitiator molecules for similar inhibition lithography processes is presented. Through implementation of tests such as Z-scan, fluorescence depletion, ultrafast transient spectroscopy and UV-Vis absorption and fluorescence measurements a promising new photoinitiator with 5-factor improvement in printing efficiency is found. Second, a projection lithography scheme is developed for rapid two-photon 3D printing. A digital micro-mirror device (DMD) is utilized for dynamic pattern generation and the effects of its dispersion properties are considered. Through a spatiotemporal focusing process, continuous 3D printing is achieved at vertical prints speeds of 1 mm s-1. Simulations performed representing this rapid printing process indicate a ~1 µm layer print feature size for large areas of exposure. Comparably, a printed vertical feature size of ~ 1 µm was achieved. Lateral feature sizes ~200 nm were also demonstrated in fabrication. A variety of complex 3D structures are printed for demonstration of the spatiotemporal focusing projection lithography process including millimeter scale objects with micrometer scale 3D features. Finally, resolution enhancing strategies are implemented into the continuous, projection two-photon lithography technique. An investigation of the inhibition properties of a variety of photoinitiator systems for inhibiting polymerization achieved with low repetition rate laser exposure is presented. A planar polymerization inhibiting region is generated by creating a light sheet propagating perpendicularly to the projection printing plane.