Hybrid plasmonic molecules

Abstract

Artificial plasmonic molecules, i.e. nanoparticles that are separated by a nanometer gap, show strong near-field coupling. The gap ‘hot-spot’ exhibits new resonance features,1 and is used for a variety of plasmonic applications including sensing, imaging, and lithography.2 However, all of these applications require highly uniform gap structures, which are challenging to grow using existing nanofabrication methods, since material, size, gap, and geometry need to be engineered with nanometer accuracy. Here we report the successful fabrication of plasmonic molecules in large numbers (billions), including dimers and trimers, with precise control over their material composition (e.g. gold and silver), size (< 5 nm resolution), gap dimension (atomic resolution), and orientation on the wafer. We demonstrate that a physical shadow growth method, which is described in earlier reports,3,4is, in conjunction with atomic layer deposition, able to grow plasmonic dimers with a nanometer-sized dielectric at the wafer scale. We describe how we can precisely engineer the structural parameters of the plasmonic molecules and thus tune their corresponding coupled resonances across the entire visible spectrum. Our fabrication method can even progressively control the symmetry of the dimer and trimer structures across an entire wafer while preserving a nanogap. Furthermore, we spectroscopically map the resonances and qualitatively model the spectra. Theory and experiment are in good agreement with numerical calculations. While thus far dimer structures have largely been obtained by random drop casting, we show that we can systematically obtain identical dimers and also identical dimers where one of several parameters is systematically changed across the wafer. We expect that the structures will be important for spectroscopic studies.

1. C. Yi et al., PNAS, 2017, 114, 11621-6. 2. N. Zohar, L. Chuntonov, and G. Haran, J Photochem Photobio C 2014, 21, 26-39. 3. A. G. Mark, J. G. Gibbs, T.-C. Lee and P. Fischer, Nature Materials, 2013, 12, 802-807. 4. H.-H. Jeong, M. Alarcoon-Correa, A.G. Mark, K. Son, T.-C. Lee, and P. Fischer, Adv Sci, 2017, 4, 1700234.