On the limitations introduced by energy spread in elastic recoil detection analysis

Improvements in experimental techniques have led to monolayer depth resolution in heavy ion elastic recoil detection analysis (HI-ERDA). Evaluation of the spectra, however, is not trivial. The spectra, using even the best experimental set-up, are subject to finite energy resolution of both extrinsic and intrinsic origin. A proper account for energy spread is necessary to extract the correct depth profile from the measured spectra. With calculation of the correct energy (or depth) resolution of a given method. one can decide in advance whether or not the method will resolve details of interest in the depth profile. To achieve the best depth resolution, it is also possible to find optimum parameters for the experiments. The limitations introduced by the energy spread effects are discussed. An example for simulation is shown for high energy resolution HI-ERDA measurements. Satisfactory agreement between the simulated and the measured HI-ERDA spectra taken by 60 MeV I-127(23-) ions on highly oriented pyrolythic graphite (HOPG) sample is found, in spite of the non-equilibrium charge state of the recoils and the difference in the stopping powers caused by the given charge state of the incident ion and the recoil, which are not taken into account. To achieve more precise data evaluation these effects should be included in simulation codes, or all the subspectra corresponding to different recoils charge states should be measured and summed. (C) 2001 Elsevier Science B.V. All rights reserved.