Transparent conductive oxides (TCOs) have strong potential for plasmonic applications. Given their easily tunable properties and low energy response, significant challenges in the controlled fabrication and precise characterization of TCOs must be better understood before this potential can be realized. Here, the mid‐ to near‐infrared plasmonic response of Sn‐doped In2O3 (ITO) nanostructures is presented, fabricated top‐down using electron beam lithography and radio‐frequency sputtering. These equilateral ITO triangles of different side lengths are imaged at high spatial and energy resolution with monochromated electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope. Applying the Richardson–Lucy (RL) deconvolution algorithm to experimental EELS spectra reveals localized surface plasmon (LSP) excitations between 150 and 550 meV and a 730 meV bulk plasmon. This very‐low‐energy response to an electron beam is compared with boundary element method simulations of nanostructures. These simulations use the dielectric functions of continuous thin films of the same materials, characterized by ellipsometry, 4‐point probe, and Hall effect tests. Additionally, upon rapid thermal annealing of ITO, blue‐shifts in LSP energy, and longer LSP lifetimes are examined as a consequence of an amorphous‐to‐polycrystalline transformation and an increase in the free carrier density.

Nanometric gaps in plasmonic structures can lead to huge optical near fields and, related, to strongly enhanced interaction of molecules and light. Nanocavities formed by sphere-on-film or cube-on-film systems were recently established as promising systems, eventually reaching the strong coupling regime. However, such structures are limited with respect to being bound to a surface and by having no means of adjusting the resonance wavelength to the requirements of arbitrary analytes, independent of the gap width. We suggest and investigate in this paper silver−gold compound nanocuboid dimers in colloidal solution as potential structures to mitigate both limitations. We analyze the dimers' plasmonic properties by a combination of optical spectroscopy, electron energy loss spectroscopy, and numerical simulations, focusing on the longitudinal dimer geometry and the dominant light-coupled plasmon mode. We then calculate optical field enhancements under light and electron excitation to assess the cuboid dimer's potential in sensing and spectroscopy applications.

Surface plasmon resonances (SPR) are coherent, collective oscillations of conduction electrons confined on the surface of conductive nanostructures. The behaviour of the SPR is determined by the shape, size, and composition of the nanostructure, as well as the surrounding dielectric environment. A given nanostructure may support many different SPRs, each defined by its energy and spatial field distribution. A nanostructure supporting SPR acts as a nano-antenna, interacting with light and paving the way for application of SPRs in areas such as metamaterials [1], sensitive sensors [2], or integrated nano-circuitry [3]. The design of the nanostructure is key to its performance in each application area; we are studying the behaviour of SPR modes in different nanostructures to build the toolbox to enable intelligent design of nanostructures for a given application.