Thickness-Dependent Drude Plasma Frequency in Transdimensional Plasmonic TiN

Plasmonic transdimensional materials (TDMs), which are atomically thin metals of precisely controlled thickness, are expected to exhibit large tailorability and dynamic tunability of their optical response as well as strong light confinement and nonlocal effects. Using spectroscopic ellipsometry, we characterize the complex permittivity of ultrathin films of passivated plasmonic titanium nitride with thicknesses ranging from 1 to 10 nm. By measuring passivated TiN, we experimentally distinguish between the contributions of an oxide layer and thickness to the optical properties. A decrease in the Drude plasma frequency and increase in the damping in thinner films is observed due to spatial confinement. We explain the experimental trends using a nonlocal Drude dielectric response theory based on the Keldysh-Rytova (KR) potential that predicts the thickness-dependent optical properties caused by electron confinement in plasmonic TDMs. Our experimental findings are consistent with the KR model and demonstrate quantum-confinement-induced optical properties in plasmonic transdimensional TiN.

Automated summary

In this study, the optical properties of ultrathin films of passivated titanium nitride with thicknesses ranging from 1 to 10 nm were characterized. The experimental results showed that the plasma frequency of the films decreased and the damping increased as the thickness decreased. A theoretical model based on the Keldysh-Rytova potential was used to explain the experimental trends, confirming the thickness-dependent optical properties caused by electron confinement in the plasmonic transdimensional materials.