3D hydrogen microscopy with sub-ppm detection limit

Coincident elastic proton-proton scattering at a 17 MeV microprobe is used to investigate hydrogen distributions on microscopic scale inside freestanding samples up to some 100 mum thickness. Hydrogen imaging at atomic ppm level needs a total count rate of about 100 kHz of scattered protons in order to get sufficient statistics from the small fraction of coincident hydrogen signals. It is obtained using a highly segmented silicon strip detector of 2.3 sr for proton currents of less than 100 pA impinging on films thicker 10 mum. A five level filter almost completely suppresses accidental coincidences. The sensitivity of this kind of 3D hydrogen microscopy is demonstrated by the analysis of a 55 mum thick synthetic diamond layer showing a detection limit of 0.08 at-ppm hydrogen. In addition, the proposed depth resolution of 3-6 mum is experimentally confirmed and a lateral resolution of 0.6 mum full width half maximum is obtained at a significant hydrogen enhancement inside the layer. (C) 2004 Elsevier B.V. All rights reserved.