In-Situ Measurement of He + Stopping in Si Layers by Low-Energy Ion-Scattering Spectroscopy

We investigated the energy loss process for 2.0-keV He+ beams in amorphous Si(a-Si) by using low-energy ion-scattering spectroscopy. A-Si layers with thicknesses ranging from 2.0 to 8.0 nm were formed on Ge(2 monolayers)/Si(100) by molecular beam epitaxy under ultrahigh vacuum conditions. Backscattering measurements were performed in situ so as not to change their surfaces. The Ge peak shifted with the thickness of the a-Si overlayer, indicating an energy loss from 1.3 to 2.0-keV He+ in the a-Si layer. The obtained experimental energy shifts were compared with those calculated by Lindhard and Scharff (LS) and Ziegler, Biersack and Littmark (ZBL). The present results generally agree with their theoretical calculations.