Unconventional Approaches to High Throughput Nanolithography and 3D Printing

Hedrick, James Lupton

doi:https://doi.org/10.21985/n2-dacj-ws09

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Unconventional Approaches to High Throughput Nanolithography and 3D Printing

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This thesis centers around the development and application of novel high throughput lithography tools. These advances help: 1) establish the field of nanocombinatorics, where massive libraries (termed megalibraries) of materials can be prepared in a positionally encoded manner and then screened for functional activity, and 2) advance stereolithographic 3D printing of materials by increasing the throughput, materials compatibility, and the size of the structures that can be made. The latter has significant implications for using 3D printing in the field of manufacturing. The first four chapters focus primarily on developing nanolithography systems to better study the properties of nanostructures as a function of size and composition. Chapter 5 shifts from the nanoscale to the macroscale by building off the findings in the previous chapters and applying it to stereolithography. Finally, Chapter 6 looks towards the future of lithography and the next possible steps in the progression of these and related lithographic tools. Chapter 1 introduces cantilever-free scanning probe lithography (CF-SPL) as a powerful tool in the emerging field of nanocombinatorics. At the nanoscale, small changes in the size and composition of materials can dramatically affect their chemical reactivity, catalytic activity, energy capture capabilities, and mechanical properties. To probe material properties at these length scales, specialized tools are needed for both synthesizing and characterizing them. In addition to controlling size and composition, new tools must be developed to efficiently probe the possible combinations. The development of CF-SPL techniques has allowed inexpensive, reproducible, and high throughput patterning of both hard and soft nanomaterials over large areas (> 1 cm2). Chapter 2 addresses the problem of patterning uniformity and density limitations that have traditionally limited CF-SPL. Polymer pen lithography (PPL) utilizes an array with millions of pyramidal pens to deposit single attoliter features on a surface. However, the pen array is composed of a soft polymer that results in increased feature sizes due to poor control over the force applied by the pens on the surface. Extending this technology to include a hard-transparent array that exhibits a force-independent contact area improves its patterning capability by reducing the minimum feature size (~40 nm), minimum feature pitch (<200 nm for polymers), and pen-to-pen variation. Chapter 3 examines the use of CF-SPL to create megalibraries and its implication on the field of nanocombinatorics and materials discovery. The ability to synthesize millions of particles on a single 4 cm2 chip in parallel creates an unprecedented way to explore the materials genome. This is done through a dual spray coating approach to deliver ink to polymer pen lithography (PPL) arrays in which combinatorial libraries with size and composition gradients can be synthesized, creating a platform for printing complex nanoarrays for screening. Combining this new inking system with a materials synthetic strategy such as scanning probe block copolymer lithography (SPBCL) enables the printing of nanoparticle libraries, with features that systematically vary in terms of size and composition. Such libraries then can be screened for different properties. The nanoparticle library can include structures composed of single metals, metal oxides, multimetallic alloys, and janus structures. This novel approach enables the synthesis and screening of an extraordinarily large material parameter space. Chapter 4, like Chapter 2, addresses the problem of patterning uniformity and density limitations that have traditionally been inherit to CF-SPL with systems that deliver energy rather than materials. Beam pen lithography (BPL) is built upon platform related to PPL, but where the tips are used as light guides to pattern photochemically. Pen-to-pen height variation from the array fabrication process results in non-uniform apertures, a major problem that limited the wide-spread use of BPL. Previous aperture fabrication methods relied on spin coating photoresist onto uniform arrays which works to some extent for thousands of pens but no longer possible when scaling to millions of pens in a single array. To overcome this problem, a new type of etching technique was invented to make more uniform apertures: liquid mask etching. Utilizing a liquid mask enables the protection of the BPL arrays in a uniform way regardless of height. This results in the synthesis of 2.84 million uniform apertures with sizes as low as 250 nm. These new arrays are then used in the development of a CF-SPL nano 3D printer that utilizes the liquid mask as protection during printing. Chapter 5 builds on the nano 3D printer from Chapter 4 but takes it out of the CF-SPL system and explores it in the opposite end of the length scale spectrum. With High Area Rapid Printing (HARP), it is possible to fabricate 3D printed parts at an unprecedent rate. As a proof-of-concept, a printer utilizing HARP was built with continuous vertical print rates exceeding 430 mm/hr with a record-breaking throughput of 3.75 ft3/hr. Chapter 6 discusses the future of CF-SPL and HARP. There is a bright future for both nanolithography and additive manufacturing. While neither are in their infancy, both can still dramatically change our lives.

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