Tools and Methods for High-throughput Materials Synthesis Using Cantilever-free Scanning Probe Lithography

Golnabi, Rustin

doi:https://doi.org/10.21985/n2-fzm3-gk86

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Tools and Methods for High-throughput Materials Synthesis Using Cantilever-free Scanning Probe Lithography

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The advancement of nanotechnology is at least partially dependent on the ability to synthesize and arrange complex nanostructures on a substrate. Nanolithography, or the patterning of materials at the sub-micrometer length-scale, has been traditionally performed using a number of methods such as conventional photolithography, ion-beam etching, and electron-beam lithography. While most of these techniques demand complex multi-step procedures, often including vacuum environments, one recent development, polymer pen lithography (PPL), is a desktop fabrication tool that can be used to synthesize materials on a substrate at ultra-high-throughput and under ambient conditions. The technique uses an elastomeric array of pyramidal tips to physically transfer an ink to a substrate with the help of an atomic force microscopy (AFM) piezo. High-throughput lithography techniques like PPL have established the field of nanocombinatorics, where megalibraries of materials are synthesized over a single substrate and screened for their properties. Advancing these lithography techniques such that we can perform all kinds of materials synthesis, including electrochemical or thermal synthetic methods in-situ, will greatly enhance our capabilities to create and use these combinatorial megalibraries. In addition, new high-throughput lithography techniques may enable simpler single-substrate biological studies and open the door to massively parallel 3D nanoprinting. In this thesis, I developed and investigated four different, yet inter-related cantilever-free scanning probe lithography techniques that expand lithography into unconventional materials synthesis localized to a tip. Chapter 1 first reviews the traditional and newly emerging high-throughput lithography techniques as well as the path that has led towards the development of PPL. Chapter 2 describes a novel technique to use the existing technology to perform negative (rather than positive) lithography over a large substrate, while also investigating the technique's versatility in environments and inks as exemplified by DNA-nanoparticle assemblies within an aqueous system. Chapter 3 describes a technique termed thermal polymer pen lithography (t-PPL) and how it can be used to pattern over large areas. . This system may be used to either deliver heat directly to a thermally sensitive substrate or deliver thermally-sensitive materials to a substrate with precision using a heated pen array. In Chapter 4, an invention called electrochemical PPL (ePPL) is described, wherein the typical elastomer pen array is replaced with a hydrogel one, and a potential difference is used to locally reduce metals onto a cathodic surface. Alloy nanostructures can be synthesized using this technique across large areas, achieving control over feature size, composition, and placement. Resolution down to 210 nm and height control up to a few microns is observed. Next, Chapter 5 describes the conceptual design and fabrication of an optoelectronic heater to be used for photo-actuated PPL. Due to the use of a single backing layer in this technique, PPL is intrinsically limited to the repetition of patterns over a single large-area substrate. This work represents one possibility for using light to actuate individual pens and pattern features arbitrarily at both high speed and high-throughput. The optoelectronic heater provides 1.5 microns of PDMS expansion, with sub-second time response in the current-profile. Finally, Chapter 6 summarizes these advances and provides a future outlook for these techniques and the field of massively parallel nanolithography as a whole. Each of these innovative methods represents a distinct path forward for nanolithography with conditions and materials that have been hitherto unavailable to scientists and researchers. With each new tool and technology, newavenues for exploration are revealed in the fields of combinatorics, prototyping, and cellular studies.

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