Because of a combination of shadowing, blocking, and low ion survival probability, peaks observed in low-energy He + scattering (ISS) primarily result from the scattering of He + from single atoms in the top-most sample layer. Scattering from subsurface atoms primarily contributes to a broad background signal,as do multiple scattering events. Thus, for samples of Pt n clusters deposited on alumina, all of which containing the same total number of Pt atoms, the intensities of the Pt ISS peaks reflect the fraction of Pt atoms exposed in the surface layer. For cluster isomers with a single layer on the support, the Pt ISS intensities should be high, but if multi-layer isomers or structures are present, the intensity would be reduced, as only the topmost layer is efficiently detected. any small day-to-day variations in ISS detection sensitivity. As noted, separately prepared samples were used for the "before" and "after" samples, to avoid the effects of He + beam damage on the "after" data.