Depth profiling of light elements using elastic recoil coincidence spectroscopy (ERCS)

We have developed elastic recoil coincidence spectroscopy (ERCS), a technique with high sensitivity to profile light elements, ranging from H up to O, in thin polymer foils or in thin samples containing heavier elements. In this technique, MeV He+ ions are incident on a thin target, typically 2 μm thick, and the energies of both the forward-scattered He ions and the elastically recoiled light atoms are detected in coincidence. Concentration-versus-depth profiles can be derived from the measured number of coincidence events for a depth range of up to 1 μm and for all recoiled light elements. This is done by relating each pair of energies of scattered and recoiled atoms to a depth where scattering has occurred and to the mass of the recoiled elements. To analyze the coincidence spectra and to derive concentration-versus-depth profiles, computer programs have been developed. To demonstrate the capabilities of ERCS we have chosen polycarbonate films (48 at.% C, 9 at.% O) and have derived the expected uniform concentration-depth profiles from the coincidence spectra for a depth range of 1 μm. In a second experiments, ERCS was applied to profile B and O in a thin boron-diffused Si window. (orig.)