Collaborative Research: Designing Organometallic Precursors for Focused Electron Beam Induced Deposition of Metal Nanostructures

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As electronic devices such as smartphones become smaller but have more capability, it is important to be able to create very tiny metal structures whose physical and chemical properties can be tailored for specific applications. This requires control over not only structure, size and shape but also chemical composition. In this project, methods are being developed for patterning metals into nanoscale objects by using chemical reagents and electrons. Students involved in this project present their work at scientific meetings and publish papers in peer reviewed journals. They also have the opportunity to conduct experiments at Oak Ridge National Laboratory, broadening their educational experience while enhancing opportunities for future career placement. To communicate the excitement of science to the general public, participants in the project are generating a series of 90-second "Tiny Tech" radio modules and podcasts that feature real world applications of chemistry and chemistry-based nanoscience. Focused electron beam induced deposition (FEBID) is a promising nanofabrication technique that can create metal-containing nanostructures for photonics, catalysis, sensing and plasmonics. In this technique, electrons are used to induce local decomposition of organometallic precursors adsorbed onto solid substrates in a vacuum environment. FEBID combines the advantages of direct-write lithographic processes (e.g., high spatial resolution, site-specificity, mask-less, resist-less) with the flexibility to deposit materials on non-planar surfaces, allowing creation of spatially and geometrically well-defined three-dimensional, metal-containing nanostructures. For FEBID to emerge as a broadly applicable nanofabrication technique, however, control must be exerted over not just the size and shape, but also the chemical composition of the nanostructures. The current practice is to use precursors designed for thermal processes, such as chemical vapor deposition (CVD). These CVD precursors generally create FEBID deposits with high levels of organic contamination, limiting potential applications. This project is addressing the issue of contamination in FEBID materials. This research synthesizes and evaluates new organometallic precursors designed specifically for FEBID. The efforts are guided by mechanistic insights from surface science. They are also improved by developing new purification strategies for FEBID nanostructures. The results are improving the understanding of FEBID by generating detailed mechanistic information on the electron-molecule reactions. Careful design of the reaction chemistry allows control of the purity while the ability to focus electron beams allows control of the size and shape of the metal structure in a process analogous to 3D printing of plastic objects.