Fabrication and Growth Control of Metal Nanostructures through Exploration of Atomic Force Microscopy-Based Patterning and Electroless Deposition Conditions

• Published in: Journal of physical chemistry. C 2020-11, Vol.124 (46), p.25588-25601
• Main Authors: Edwards, Christina M, Ulapane, Sasanka B, Kamathewatta, Nilan J. B, Ashberry, Hannah M, Berrie, Cindy L
• Format: Article
• Language: English
• Subjects: C: Physical Processes in Nanomaterials and Nanostructures
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.0c08017

Applications such as biosensing, plasmonics, and nanoelectronics require nanoscale metal structures with controlled dimensions and placement. However, significant challenges remain in the fabrication of metal nanostructures of controlled size, shape, and placement on a solid support. Among these challenges are precise positional control at the nanoscale, flexibility and tunability in shape, and the cost and complexity of methods. This work presents the development and exploration of methods for the fabrication of copper, silver, and gold (Cu, Ag, and Au) nanostructures directly on silicon (Si) substrates through the use of atomic force microscopy (AFM)-based nanofabrication using a self-assembled monolayer (SAM) resist followed by metal deposition in the structure using electroless deposition (ELD). The importance of the role of the SAM resist layer is highlighted, as it is critical to prevent metal deposition on the areas of the substrate outside the desired pattern. We have found that octadecyltrichlorosilane (OTS) monolayers are much more robust and resistant films for the ELD process than either octadecyl SAMs, formed from alkenes on hydrogen-terminated Si, or octadecyldimethylchlorosilane (ODMS) SAM films. In addition, the patterning parameters used for the AFM-based fabrication, the ELD solution parameters, and the role of doping of Si have been explored and together the results suggest that with proper tuning of the ELD solution concentrations and the use of a robust SAM resist film, such as OTS, tunable metal nanostructures are achievable. This is demonstrated here for Cu, Ag, and Au, but the process should be adaptable to a variety of metals, as long as the redox potentials are compatible with the oxidation of Si. Importantly, this method exploits the exquisite tunability of AFM-based lithography to provide precise control over the size, shape, and position of the metal nanostructure. This provides significant advantages for prototyping of new structures, as well as fundamental investigations of the properties of such nanostructures.