Non-Rutherford backscattering microscopy using 25 MeV protons

Abstract

Protons at energies between 10 and 25 MeV are a very sensitive probe for hydrogen using coincident proton–proton scattering with the possibility for depth profiling samples up to several 100 μm thickness. At the Munich microprobe SNAKE we have developed this method for sensitive 3D hydrogen microscopy [1]. In parallel to sensitive 3D hydrogen microscopy by proton–proton scattering we introduce a non-Rutherford backscattering analysis utilizing 25 MeV protons in order to obtain 3D depth profiles of all major elements. We present energy spectra of backscattered protons at various thin and thick film samples of pure elements which we use as fingerprints to analyse more complex materials like minerals or metals. It is due to the low stopping power of the high energy protons that the depth profiles of several elements do not or do only partially overlap when analysing freestanding samples with thicknesses in the 100 μm range. The merit of our method is that signals of the light elements may not be affected by heavier matrix elements. Analysing thin films smaller than 5 μm we have achieved a mass resolution of Δ A / A ≤ 1 / 28 for non-overlapping mass signals utilizing a 5 mm thick Si(Li)-detector.