Ab Initio Simulation of Position-Dependent Electron Energy Loss and Its Application to the Plasmon Excitation of Nanographene

We present a newly developed ab initio simulation method of the position-dependent electron energy loss and employ it to study the plasmon excitation of the zigzag-edged nanographene. This method enables us to not only simulate the spatially resolved electron energy loss spectra (EELS) but also discover the localization characteristics in the plasmon excitation in the imperfect surfaces or two-dimensional materials. The calculation results of the zigzag-edged nanographene show some strong pi and pi + sigma plasmon peaks with fast electrons incident to the nanographene flake. Edge incidence induces a strong plasmon excitation, which originated from the transition of edge-to-edge states. The spatial resolution of pi and pi + sigma plasmons in nanographene was discovered by the positional scanning of simulated EELS of nanographene. To quantitatively characterize the effect of edge states on the plasmon excitation of nanographene, we employed the cosine similarity metric to analyze the line-scan energy-loss spectrum of nanographene and found that the plasmon excitation caused by the edge states is mainly confined in the distances of similar to 5.07 and similar to-3.93 angstrom with respect to the corner and edge of nanographene, respectively. These results provide important information for nanographene in nanoscale plasmon applications.