HIGH DEPTH RESOLUTION ERDA OF H AND D BY MEANS OF AN ELECTROSTATIC SPECTROMETER

In the standard elastic recoil detection analysis of H and D the energy resolution and - as a consequence - also the depth resolution are limited by essentially three effects: the kinematic errors due to the finite size of the beam spot on the target and of the solid angle of the detector, the finite energy resolution of the commonly used silicon surface-barrier detectors, and the energy straggling of the recoil ions in the shielding foil in front of the detector. By the use of an electrostatic spectrometer the first two effects can be reduced considerably, while the third effect is eliminated completely. The present paper describes an experimental setup employing such a spectrometer. With this setup an energy resolution of DELTAE = 3.3 keV has been obtained in case of the analysis of H and of DELTAE = 4.5 keV in case of D in near surface layers. It corresponds to depth resolutions of 1.8 nm (H) and 1.5 nm (D) in Cu for a primary beam of 4.3 MeV Ne at an incidence angle of 19' and with the detector positioned at a recoil angle of 38-degrees. With grazing incidence (5-degrees) and a slightly improved setup a depth resolution in the monolayer range should be obtainable. The paper discusses the different effects contributing to the energy resolution and gives various examples for applications which include the analysis of D2O on an oxidized silicon surface and of H and D on a clean copper surface. In a final section the performance of the present setup is compared with that of the well known N-15 resonance technique commonly used for the analysis of hydrogen.