Plasmons in MoS₂ studied via experimental and theoretical correlation of energy loss spectra

This paper takes a fundamental view of the electron energy loss spectra of monolayer and few layer MoS₂ . The dielectric function of monolayer MoS₂ is compared to the experimental spectra to give clear criteria for the nature of different signals. Kramers-Krönig analysis allows a direct extraction of the dielectric function from the experimental data. However this analysis is sensitive to slight changes in the normalisation step of the data pretreatment. Density functional theory provides simulations of the dielectric function for comparison and validation of experimental findings. Simulated and experimental spectra are compared to isolate the π and π + σ surface plasmon modes in monolayer MoS₂ . Single-particle excitations obscure the plasmons in the monolayer spectrum and momentum resolved measurements give indication of indirect interband transitions that are excited due to the large convergence and collection angles used in the experiment. LAY DESCRIPTION: Two-dimensional materials offer a path forward for smaller and more efficient devices. Their optical and electronic properties give way to beat the limits set in place by Moore's Law. Plasmon are the collective oscillations of electrons and can confine light to dimensions much smaller than its wavelength. In this work we explore the plasmonic properties of MoS₂ , a representational candidate from a family of 2D materials known as transition metal dichalcogenides. High resolution electron microscopy and spectroscopy provide insights in the plasmonic properties of MoS₂ down to an atomic scale. Experimental results show the relationship between plasmons and interband transitions in the electron energy loss spectrum. Density functional theory provides a theoretical support for the experimental findings and provides commentary on the fundamental underlying physics.