Angular scattering of protons through ultrathin graphene foils: Application for time-of-flight instrumentation

Space plasma instruments often rely on ultrathin carbon foils for incident ion detection, time-of-flight (TOF) mass spectrometry, and ionization of energetic neutral atoms. Angular scattering and energy loss of ions or neutral atoms in the foil can degrade instrument performance, including sensitivity and mass resolution; thus, there is an ongoing effort to manufacture thinner foils. Using new 3-layer graphene foils manufactured at the Los Alamos National Laboratory, we demonstrate that these are the thinnest foils reported to date and discuss future testing required for application in space instrumentation. We characterize the angular scattering distribution for 3-30 keV protons through the foils, which is used as a proxy for the foil thickness. We show that these foils are ∼2.5-4.5 times thinner than the state-of-the-art carbon foils and ∼1.6 times thinner than other graphene foils described in the literature. We find that the inverse relationship between angular scattering and energy no longer holds, reaffirming that this may indicate a new domain of beam-foil interactions for ultrathin (few-layer) graphene foils.