Infrared Localized Surface Plasmon with Curved Electron Trajectory

Abstract

been introduced into optoelectronic devices for the enhancement of chargecarrier generation. [21,22] LSP devices or structures working in the infrared [23][24][25] and in the terahertz spectra [26][27][28][29][30] are of special interest to different application fields. In such cases, micrometer-or even millimeter-scale structures have to be fabricated to accomplish the resonance in the target spectral range. On one hand, this will ease the fabrication techniques due to the much-lowered resolution requirements, on the other hand, large dimensions of the metallic structures also imply large loss, due to the large thickness of the structures for the optical field to transmit through. In particular, for the spectral range of near-infrared between 1 and 3 µm in wavelength, it is especially critical to control the structural sizes to achieve the resonance spectrum and to balance the optical loss properties. This spectral range is very important for a large variety of optoelectronic techniques and applications, including solar cells, photodetectors, light-emitting or lasing devices, sensors, or photo-actuators. However, LSPs in nanostructured metals are mostly working in the visible spectral range. Plasmonic nanoparticles, [30,31] nanospheres, [32,33] nanowires, [34,35] nanoholes, [36,37] nanorings, [38] or even more complexed nanopyramids, [39] nanostars, [40] and nanoflowers [41] have been reported. The sizes or the aspect ratios of the whole structure or some segments can be utilized as the dimensions for tuning the LSP resonance spectrum. [42][43][44][45] Using interfacial coupling between metallic nanostructures is an effective approach to redshift the LSP resonance spectrum. [46] Nevertheless, nanostructured metals with LSP resonance in the infrared are relatively less reported.In this work, we solve this challenge by constructing curve gold nanoshell (AuNS) cylindrical ridges, where the curved nanostructures not only extend largely the length of the plasmonic electron oscillation trajectory but also enhance the electronic scattering process by the strongly bent trace. Thus, the corresponding LSPs are tuned in the spectral range from 1.1 to beyond 2.5 µm simply by changing the perimeter length, the curvature angle, and the thickness of the AuNS cylindrical ridges. The photophysical mechanisms for such curved LSPs are verified both experimentally and theoretically.The construction of 3D localized surface plasmons (LSPs) in infrared using curved gold nanoshell (AuNS) cylindrical ridges is reported, where the LSPs are found to be established through electronic oscillation in curved trajectories along the perimeter of the cross-sectional profile of the AuNS cylindrical ridges. Such a design is equivalent to an extension of the electronic trajectory length or plasmonic electron-oscillation distance by the curvature length and by the enhanced electronic scattering. Strong LSPs are measured for the transverse magnetic polarization perpendicular to the extending direction of the AuNS cylindrical ridges in the spectral ra...