Until now there has been a controversy about the question if the energy loss $\Delta E$ of energetic ions in thin foils really is a linear function of the foil thickness $d$. To investigate the function $\Delta E\left(d\right)\mathrm{}$ we applied for our experiments Rutherford backscattering for foil thickness calibration. Compared to earlier experiments this method offered the advantage that no assumptions concerning the stopping power of thickness-calibrating ions like protons were implied. Beyond that any surface contamination of the targets could be analyzed that might have influenced the energy loss of the transmitted ions. The energy losses were measured with the use of a magnetic spectrometer. Our experiments confirmed a linear thickness dependence of the energy loss. Furthermore, it could be concluded that the ${\mathrm{He}}^{+}$ particles exhibit an increased preequilibrium electronic stopping power in the first atomic layers of the solid.

• Received 19 November 1981

DOI:https://doi.org/10.1103/PhysRevB.25.5591