Fabrication of nanostructures below the resolution limit of typical lithography techniques helps push the boundaries of plasmonics and nano-optics research. True nanoscale (<10 nm) metallic structures and gaps allow for plasmonic enhancement of incident light which is beneficial in various applications such as biosensing, photovoltaic absorption enhancement, surface enhanced spectroscopies, and photocatalysis. However, this high resolution can be difficult to obtain with typical techniques. A new nanomasking technique has been developed which allows for fabrication of nanostructures and nanogaps down to sizes less than 10 nm by using a two-step electron beam lithography (EBL) and deposition method with the potential for mass production scalability. This technique improves upon existing alternatives for creation of truly nanoscale features. It provides finer control, two-dimensional fabrication, and the ability to simultaneously create many plasmonic hotspots over a large area. This work has fabricated such structures with true nanoscale metal features and nanogaps. Structures can be tuned to specific wavelengths by controlling structure and gap widths. Further work will continue scaling up of the technique to understand its feasibility for mass production plasmonic enhancement and nano-optics applications.

Figure 1 Colorized SEM images of nanomasking fabrication results.
(a) Interdigital nanofinger pattern. (b) Nanowire grid pattern. From [1].

Related work and further reading

[1] S. J. Bauman, E. C. Novak, D. T. Debu, D. Natelson, and J. B. Herzog, "Fabrication of sub-lithography-limited structures via Nanomasking technique for plasmonic enhancement applications", IEEE Trans Nanotechnol 14 5 (2015).

[2] J. B. Herzog and D. Natelson, Systems and Methods for Fabricating Nanostructures and Nanogaps. US Patent Application 62/039,337, (filed August 2014).

[3] S. Bauman et al. Plasmonic structures fabricated via nanomasking sub-10 nm lithography technique SPIE (Aug 2015)

[4] S. Bauman et al. Optical nanogap matrices for plasmonic enhancement applications, SPIE Proc. (2014)

Figure 2 Scanning Electron Microscope (SEM) images of various test structures. All images are on the same scale with a micron bar of 20 microns. This is roughly the diameter of very fine human hair! Images taken with Philips Environmental SEM part of the Arkansas Nano-Bio Materials Characterization Facility.

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