Direct observation of the vanishing EELS cross section in graphene

TL;DR

This study provides the first experimental evidence of the vanishing EELS cross section in graphene at low momentum transfers, revealing the intrinsic dielectric response by accounting for kinematic suppression effects.

Contribution

It offers the first direct observation and quantification of the quenched EELS cross section in graphene at small momentum transfers, advancing understanding of 2D material spectroscopy.

Findings

Confirmed the vanishing EELS cross section at low q in graphene

Quantified the kinematic suppression effect on EEL spectra

Revealed the intrinsic dielectric response of graphene

Abstract

In transmission electron energy-loss spectroscopy, the cross section in 2D is quenched by kinematic effects once the momentum transfer becomes smaller than a critical value set by $q_z$, the momentum loss parallel to the beam. Our highly momentum ($\Delta q = 0.02$~\r{A}$^{-1}$) and energy ($\Delta E = 45$~meV) resolved setup is instrumental on delivering the unprecedented experimental verification of quenched 2D EEL spectra on freestanding graphene at momentum transfers $q$ below $0.06$\r{A}$^{-1}$. We retrieve the intrinsic uniform dielectric response of graphene from measured spectra by quantifying the kinematic suppression.