Direct observation of the vanishing EELS cross section in graphene

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 qz, the momentum loss parallel to the beam. Our highly momentum (Δ q = 0.02~{A}⁻¹) and energy (Δ 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 $0.06${A}⁻¹. We retrieve the intrinsic uniform dielectric response of graphene from measured spectra by quantifying the kinematic suppression.