Rutherford backscattering oscillation in scanning helium-ion microscopy

Scanning helium-ion microscopy (SHIM) yields high-resolution imaging and is capable of surface elemental analysis at the nanometer scale. Here we examine recently discovered SHIM backscattered intensity oscillations versus the target atomic number. These oscillations are contrary to the expected monotonic increase of the backscattered helium-ion (He⁺) rate with the atomic number of elemental samples. We explore the ion-sample interaction via numerical simulations for a variety of scattering geometries and confirm the presence of oscillations. The oscillations are attributed to the atomic rather than the nuclear structure of the target. To that end, we study the link (near anticorrelation) between backscatter rate and He⁺ beam stopping power, both versus the target atomic number. This leads us to ascribe the origin of the backscatter oscillation to the Z₂-oscillations of the stopping power in ion-beam physics, with the latter being rooted in the valence electron configuration of elemental targets.