No abstract

We present a new atomistic model for plasmonic excitations and optical properties of metallic nanoparticles, which collectively describes their complete response in terms of fluctuating dipoles and charges that depend on the local environment and on the morphology of the composite nanoparticles. Being atomically dependent, the total optical properties, the complex polarizability, and the plasmonic excitation of a cluster refer to the detailed composition and geometric characteristics of the cluster, making it possible to explore the role of the material, alloy mixing, size, form shape, aspect ratios, and other geometric factors down to the atomic level and making it useful for the design of plasmonic particles with particular strength and field distribution. The model is parameterized from experimental data and, at present, practically implementable for particles up to more than 10 nm (for nanorods even more), thus covering a significant part of the gap between the scales where pure quantum calculations are possible and where pure classical models based on the bulk dielectric constant apply. We utilized the method to both spherical and cubical clusters along with nanorods where we demonstrate both the size, shape, and ratio dependence of plasmonic excitations and connect this to the geometry of the nanoparticles using the plasmon length.

Regular arrays of plasmonic nanoparticles have brought significant attention over the last decade due to their ability to support localized surface plasmons (LSPs) and exhibit diffractive grating behavior simultaneously. For a specific set of parameters (i.e., period, particle shape, size, and material), it is possible to generate super-narrow surface lattice resonances (SLRs) that are caused by interference of the LSP and the grating Rayleigh anomaly. In this letter, we propose plasmonic structures based on regular 2D arrays of TiN nanodisks to generate high-Q SLRs in an important telecommunication range, which is quite difficult to achieve with conventional plasmonic materials. The position of the SLR peak can be tailored within the whole telecommunication bandwidth (from ≈ 1.26 μm to ≈ 1.62 μm) by varying the lattice period, while the Q-factor is controlled by changing nanodisk sizes. We show that the Q-factor of SLRs can reach a value of 2 × 103, which is the highest reported Q-factor for SLRs at telecommunication wavelengths so far. Tunability of optical properties, refractory behavior, and low-cost fabrication of TiN nanoparticles paves the way for manufacturing cheap nanostructures with extremely stable and adjustable electromagnetic response at telecommunication wavelengths for a large number of applications.