Shape-Dependent Field Enhancement and Plasmon Resonance of Oxide Nanocrystals

Metallic nanostructures can manipulate light-matter interactions to induce absorption, scattering, and local heating through their localized surface plasmon resonances. Recently, plasmonic behavior of semiconductor nanocrystals has been investigated to stretch the boundaries of plasmonics farther into the infrared spectral range and to introduce unprecedented tunability. However, many fundamental questions remain regarding characteristics of plasmons in doped semiconductor nanocrystals. Field enhancement, especially near features with high curvature, is essential in many applications of plasmonic metal nanostructures, yet the potential for plasmonic field enhancement by semiconductor nanocrystals remains unknown. Here, we use the discrete dipole approximation (DDA) to understand the dependence of field enhancement on size, shape, and doping level of plasmonic semiconductor nanocrystals. Indium-doped cadmium oxide is considered as a prototypical material for which faceted cube-octohedral nanocrystals have been experimentally realized; their optical spectra are compared to our computational results. The computed extinction spectra are sensitive to changes in doping level, dielectric environment, and shape and size of the nanocrystals, providing insight for materials design. High-scattering efficiencies and efficient local heat production make 100 nm particles suitable for photothermal therapies and simultaneous bioimaging. Meanwhile, single particles and dimers of nanocrystals demonstrate strong, shape- and wavelength-dependent near-field enhancement, highlighting their potential for applications in infrared sensing, imaging, spectroscopy, and solar conversion.