Infrared Energy Conversion in Plasmonic Fields at Two-Dimensional Semiconductors

Conversion of infrared energy within plasmonic fields at two-dimensional, semiconductive transition metal dichalcogenides (TMD) through plasmonic hot electron transport and nonlinear frequency mixing has important implications in next-generation optoelectronics. Drude-Lorentz theory and approximate discrete dipole (DDA) solutions to Maxwell’s equations guided metal nanoantenna design towards strong infrared localized surface plasmon resonance (LSPR). Excitation and damping dynamics of LSPR in heterostructures of noble metal nanoantennas and molybdenum- or tungsten-disulfide (MoS2; WS2) monolayers were examined by parallel synthesis of (i) DDA electrodynamic simulations and (ii) near-field electron energy loss (EELS) and far-field optical transmission UV-vis spectroscopic measurements. Susceptibility to second-order nonlinear frequency conversion processes, X(2), for monolayer MoS2 and WS2 were measured to be 660±130 pm V-1 and 280±18 pm V-1, respectively, by Hyper Rayleigh Scattering. Femtosecond conversion of resonant irradiation to injection of plasmonic hot electrons into the TMD were measured in EELS at a maximum of 11±5% quantum efficiency for an optimized physicochemical Au-WS2 junction. Measured nonlinear second harmonic generation (SHG) from a ca. 1 μm MoS2 monolayer was enhanced 17-84% by local electric field augmentation from a single 150 nm Au nanoshell to a conversion efficiency of up to 0.023% W-1. Capacitive coupling between nanoshells arranged into dimers further augmented SHG activity from MoS2. New theoretical and experimental insights into energy conversion interactions between coupled plasmonic and excitonic materials spanning the linear and nonlinear optical regimes were established towards their implementation as an optoelectronic platform