Hot carrier dynamics in plasmonic transition metal nitrides

Abstract

Extraction of non-equilibrium hot carriers generated by plasmon decay in metallic nanostructures is an increasingly exciting prospect for utilizing plasmonic losses, but the search for optimum plasmonic materials with long-lived carriers is ongoing. Transition metal nitrides are an exciting class of new plasmonic materials with superior thermal and mechanical properties compared to conventional noble metals, but their suitability for plasmonic hot carrier applications remains unknown. Here, we present fully first-principles calculations of the plasmonic response, hot carrier generation and subsequent thermalization of all group IV, V and VI transition metal nitrides, fully accounting for direct and phonon-assisted transitions as well as electron-electron and electron-phonon scattering. We find the largest frequency ranges for plasmonic response in ZrN, HfN and WN, between those of gold and silver, while we predict strongest absorption in the visible spectrum for the VN, NbN and TaN. Hot carrier generation is dominated by direct transitions for most of the relevant energy range in all these nitrides, while phonon-assisted processes dominate only below 1 eV plasmon energies primarily for the group IV nitrides. Finally, we predict the maximum hot carrier lifetimes to be around 10 fs for group IV and VI nitrides, a factor of 3 -4 smaller than noble metals, due to strong electron-phonon scattering. However, we find longer carrier lifetimes for group V nitrides, comparable to silver for NbN and TaN, while exceeding 100 fs (twice that of silver) for VN, making them promising candidates for efficient hot carrier extraction.

Plasmonic Enhanced Reactive Oxygen Species Activation on Low‐Work‐Function Tungsten Nitride for Direct Near‐Infrared Driven Photocatalysis

“…The real part of the dielectric function presents a negative value window between 600 and 2100 nm for WN-cub, and the image part dielectric function of WN-cub shows a peak at 1500 nm, revealing the significant NIR-plasmonic behavior the metallic WN. [16] According to above DFT calculation results, the metallic cubic WN possesses low-work function and strong plasmonic assisted NIR absorption, endowing it with more favorable electronic property as promising NIR-driven photocatalyst. Therefore, the cubic phase WN and its NIR-driven photocatalytic performance are systematically investigated in this work later.…”

From Optical to Chemical Hot Spots in Plasmonics

“…This leads to the presence of out-ofequilibrium hot-carriers at the external surface of the material, readily available to participate in surface chemical reactions. 52 We have indeed recently sensed an enhanced charge transfer pathway in Au/TiO2 composites due to the presence of oxygen vacancies in the semiconductor (Figure 7a). This produces an extra enhancement in the Raman scattering signal of a wide range of molecules, as exemplified for Rhodamine 6G in Figure 7b.…”

Dynamics and Spin-Valley Locking Effects in Monolayer Transition Metal Dichalcogenides

“…Finally, we investigate the energy distributions of carriers that are excited upon optical absorption in these materials, accounting for both direct and phonon-assisted transitions using our previously established first-principles methodology. [40][41][42][43][44][45][46][47] Fig. 5 show that direct transitions dominate carrier generation in all these materials, as expected for direct gap semiconductors where the band gap and optical gap are equal so that direct transitions are always allowed.…”

“…which is identical to (3) except for an additional final factor accounting for the scattering angle between initial and final electron band velocities v kn (defined by v ≡ ∂ε/∂k). Then, we calculate the mobility by solving the linearized Boltzmann equation using a full-band relaxation-time approximation, 40,43,55 µ(ε ) = e |n(ε )| n BZ gsdk (2π) 2 ∂f kn (ε ) ∂ε kn (v kn ⊗ v kn )τ p kn , (5) where the Fermi function derivative selects out carriers that contribute to transport at a particular doping level specified by Fermi level position ε , and where gs (= 1 with and = 2 without spin-orbit coupling) is the spin-degeneracy factor. Above, the Fermi-level dependent carrier density is defined as…”