Energy straggling of 4He ions below 2.0 MeV in Al, Ni, Pt, and Au

In recent years, backscattering spectrometry has become an important tool in the analysis of thin films. An inherent limitation, though, is the loss of depth resolution due to energy straggling of the beam. To investigate this, energy straggling of 4He ions has been measured in thin films of Ni, Al, and Au. Straggling is roughly proportional to square root of thickness and appears to have a slight energy dependence. The results are compared with predictions of Bohr's theory and with previous measurements made in Pt. While Ni measurements are in fair agreement with theory, Al measurements are 30% above and Au measurements are 40% below predicted values. The Au and Pt measurements are consistent with one another