Elastic recoil detection with single atomic layer depth resolution

Abstract

The necessary conditions for single atomic layer depth resolution in Elastic Recoil Detection (ERD) analysis will be summarized in this paper: First there are rigorous requirements for the ion beam conditions and for the energy resolution of the recoil ion detector in order to obtain an energy resolution in the order of 5 × 10 −4. Second, the most limiting factors in depth resolution are due to the physical limits imposed by small angle scattering effects and due to the energy loss spread of the incident and recoil ions. Last but not least, the third point deals with irradiation damage which has to be carefully controlled in order to measure the original depth profile before it is altered by the ion beam. As studied by energy loss measurements in transmission geometry through thin carbon foils the energy spread of heavy ions strongly depends on the charge state of the incident ions. In order to obtain the smallest energy spread the data show that the charge state of the incident ions should be near equilibrium. Using a 60 MeV 127I 23+ ion beam the resolution of single atomic carbon layers of a highly oriented pyrolythic graphite (HOPG) sample could be demonstrated analysing the 12C 5+ recoils with the Munich Q3D magnetic spectrograph. As far as we know it is the first time that separated signals of neighbouring atomic layers could be resolved using ERD.