In this work, the 2D metallic nanoprisms with a thickness of 20 ± 2 nm but lateral dimensions ranging from 500 to 1000 nm have been synthesized by a colloidal chemistry approach. Unlike lithographied systems, the crystalline nature of these structures drastically reduces scattering losses. These particles behave as two-dimensional plasmonic cavities that sustain high-order plasmonic modes bound to the edges. These electromagnetic surface modes, resulting from the longitudinal and collective oscillations of the free electrons, can be optically excited with visible light. Yet, their spectral and spatial characteristics are essentially tailored by the particle shape and size, which can only be varied within the constraints of crystal growth. In order to develop an on-demand engineering of the optical properties of the nanoprisms, subwavelength holes have been milled by focused ion beam inside these cavities. Indeed such small apertures perforated in ultra-thin gold films exhibit a broad plasmonic dipolar resonance that overlaps the spectral range of these high order plasmon modes and so can potentially modify them at will.
Using a femtosecond pulsed laser and taking advantage of the two-photon luminescence response of the hole and the cavity, the CEMES team has successfully imaged and probed the different regimes of perturbation and spatial reconstruction of the coupled hole-prism system SP-LDOS. The excellent agreeement between their theoretical model and the experimental optical data has enabled a thorough analysis of these coupling regimes, highlighting that the plasmonic states in the hole-prism systems are markedly different from those borne by a pristine cavity. A complex electromagnetic coupling regime was revealed rather than a mere superimposition of the individual resonator responses. This study is a new milestone in the design of building blocks for optical information transfer and processing at 2D based on a plasmonic modal engineering approach.
A. Cuche, S. Viarbitskaya, J. Sharma, A. Arbouet, C. Girard, and E. Dujardin. Sci. Reports 5, 16635 (2015).
Dr Aurélien Cuche : cuche chez cemes.fr