To provide additional insight into the carbon/Pt morphology, the samples were also probed by low energy He + ion scattering (ISS) before and after 6 TPDs (Fig. ). Example ISS spectra shown as insets have peaks due to He + scattering from individual Pt, Ge, Al, and O atoms in the top-most sample layer, superimposed on a smooth background from multiple or sub-surface scattering processes. The background rises sharply at lower energies, preventing direct observation of surface carbon. The main plots in Fig. show how the background-subtracted Pt and Ge peak intensities vary as a function of exposure to the ~0.35 μA He + beam, which slowly sputters materials from the surface. To compensate for any He + intensity variations, the Pt and Ge intensities are normalized to the total (Pt+Ge+Al+O) intensity, which is nearly invariant under He + exposure.