Spatially resolved quantum plasmon modes in metallic nano-films from first principles

TL;DR

This paper introduces a first-principles method to analyze spatially resolved quantum plasmon modes in metallic nano-films, revealing quantum effects and non-local responses that influence plasmon behavior at nanometer scales.

Contribution

The authors develop a spectral analysis approach to identify and compute quantum plasmon modes from first principles, applicable to ultra-thin metallic films.

Findings

Identification of surface, sub-surface, and bulk plasmon modes in nanometer-thick Na films.

Quantum confinement and non-local effects significantly alter plasmon modes.

The method provides intuitive understanding of collective excitations and spectra interpretation.

Abstract

Electron energy loss spectroscopy (EELS) can be used to probe plasmon excitations in nanostructured materials with atomic-scale spatial resolution. For structures smaller than a few nanometers quantum effects are expected to be important, limiting the validity of widely used semi-classical response models. Here we present a method to identify and compute spatially resolved plasmon modes from first principles based on a spectral analysis of the dynamical dielectric function. As an example we calculate the plasmon modes of 0.5-4 nm thick Na films and find that they can be classified as (conventional) surface modes, sub-surface modes, and a discrete set of bulk modes resembling standing waves across the film. We find clear effects of both quantum confinement and non-local response. The quantum plasmon modes provide an intuitive picture of collective excitations of confined electron systems and offer a clear interpretation of spatially resolved EELS spectra.