Metasurfaces, and in particular those containing plasmonic-based metallic elements, constitute an attractive set of materials with a potential for replacing standard bulky optical elements. In recent years, increasing attention has been focused on their nonlinear optical properties, particularly in the context of second and third harmonic generation and beam steering by phase gratings. Here, we harness the full phase control enabled by subwavelength plasmonic elements to demonstrate a unique metasurface phase matching that is required for efficient nonlinear processes. We discuss the difference between scattering by a grating and by subwavelength phase-gradient elements. We show that for such interfaces an anomalous phase-matching condition prevails, which is the nonlinear analogue of the generalized Snell's law. The subwavelength phase control of optical nonlinearities paves the way for the design of ultrathin, flat nonlinear optical elements. We demonstrate nonlinear metasurface lenses, which act both as generators and as manipulators of the frequency-converted signal.
We present an electrically driven plasmonic device consisting of a gold nanoparticle trapped in a gap between two electrodes. The tunneling current in the device generates plasmons, which decay radiatively. The emitted spectrum extends up to an energy that depends on the applied voltage. Characterization of the electrical conductance at low temperatures allows us to extract the voltage drop on each tunnel barrier and the corresponding emitted spectrum. In several devices we find a pronounced sharp asymmetrical dip in the spectrum, which we identify as a Fano resonance. Finite-difference time-domain (FDTD) calculations reveal that this resonance is due to interference between the nanoparticle and electrodes dipolar fields, and can be conveniently controlled by the structural parameters. Electrically driven plasmonic devices may offer unique opportunities as a research tool and for practical applications [1][2][3][4][5] . In such devices, current that flows across a metallic tunnel junction
We study metal–insulator–semiconductor tunnel junctions where the metal electrode is a patterned gold layer, the insulator is a thin layer of Al 2 O 3 , and the semiconductor is p-type silicon. We observe light emission due to plasmon-assisted inelastic tunneling from the metal to the silicon valence band. The emission cutoff shifts to higher energies with increasing voltage, a clear signature of electrically driven plasmons. The cutoff energy exceeds the applied voltage, and a large fraction of the emission is above the threshold, ℏω > eV . We find that the emission spectrum manifests the Fermi–Dirac distribution of the electrons in the gold electrode. This distribution can be used to determine the effective electron temperature, T e , which is shown to have a linear dependence on the applied voltage. The strong correlation of T e with the plasmon energy serves as evidence that the mechanism for heating the electrons is plasmon decay at the source metal electrode.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.