Hydrogen Microscopy

A unique and most sensitive 3D hydrogen microscopy setup using the proton proton scattering method has been installed at the Munich particle accelerator. Thin foils or thick layers (30 µm (Tungsten) - 180 µm (Silicon)) can be investigated. For this, a proton beam at an energy up to 30 MeV is focused onto the sample. When entering the sample, the protons scatter from atoms of all elements in the sample. However, if a proton hits a hydrogen nucleus, so also a proton, it gives a special scattering reaction: Compared to balls in a classical billard game, the to particles exit with exactly 90° to each other because of the equal mass. The scattering event is detected with this angular correlation with a structured detector and a coincidence in a small time window. With this, the background from all other scattering events is eliminated nearly completely. Also, the probability for a proton-proton-scattering process is known very well. Hence, with the known number of incident protons it is possible, to analyse the hydrogen content in an absolute way without any material dependent calibration.

At the microprobe SNAKE, a lateral resolution (beam focus) of about 1 µm is achieved. The depth resolution of the method is in the micrometer range as well. At polycristalline diamond we already achieved a sensitivity less than 0.08 at-ppm (8 hydrogen atoms on 100 Millions carbon atoms). [P. Reichart et al., Three-Dimensional Hydrogen Microscopy in Diamond. Science, 306 (2004) 1537]. (Download: FREE pdf, supporting online material). Further publications, please see or SNAKE Homepage.