Optical trapping using nanoapertures in metal films has advanced significantly in recent years, allowing for the trapping of nanoparticles in the single digit nanometer range, including proteins. It has been recognized previously by theoretical studies coaxial that apertures with small gaps in a metal film can provide extremely large trapping potentials for such nanoparticles. However, past approaches to nanofabrication, such as focussed ion beam milling, do not reliably produce sub-10 nm features. Here we demonstrate the use of a combined electron-microscopy and atomic layer deposition approach to reliably fabricate sub-10 nm gaps on the wafer scale. We achieve trapping of polystyrene nanoparticles and proteins using these apertures. Numerical simulations show the steep trapping potential achieved in a resonantly tuned coaxial structure. The coaxial structures fabricated are also measured to ensure the wavelength of the resonance is close to the trapping laser wavelength. As nanogap structures are also promising for surface-enhanced Raman scattering (SERS) and surface-enhanced infrared absorption, our devices can act as a multifunctional platform to integrate single-molecule manipulation and spectroscopic analysis.

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Daehan Yoo, Gurunatha K. Laxminarayana, Daniel Mohr, Han-Kyu Choi, Reuven Gordon, and Sang-Hyun Oh, "Optical trapping of nanoparticles and proteins with resonant coaxial nanoapertures using 8-nm gaps (Conference Presentation)," Proc. SPIE 10723, Optical Trapping and Optical Micromanipulation XV, 1072319 (Presented at SPIE Nanoscience + Engineering: August 22, 2018; Published: 17 September 2018); https://doi.org/10.1117/12.2320423.5836018671001.