Increased Accuracy and Sensitivity in Hydrogen Analysis

(1) Universität der Bundeswehr München, LRT2, 85577 Neubiberg, Germany
(2) Regroupement Québécois sur les Matériaux de Pointe, Département de Physique, Université de Montréal, Montréal, QC H3C 3J7, Canada

Proton-proton (pp) scattering has proven to be the most sensitive ion beam method for hydrogen depth profiling [1]. For microscopic imaging in 3 dimensions it is in fact the only usable method because of its low radiation damage potential and its compatibility of using a large solid angle detector arrangement at a proton microprobe [2].   The high sensitivity is achieved by a narrow coincidence filter set on the detection of both protons from a pp-scattering event. In order to reduce background from accidental coincidences additional constraints are required, e.g. filtering the 90° scattering angle of both particles to each other, that is well defined due to equal masses of the scattered particles, using an angular resolving strip detector. The efficiency in the detection of pp-events, however, is reduced for tight filters due to multiple (small angle) scattering of the scattered protons for long path length in particular when analyzing hydrogen in samples containing high Z elements. Hence, the detection efficiency is a function of depth and the filter tightness. Additionally, detector effects due to its granularity and calibration uncertainties have to be carefully controlled.   Accuracy in quantification strongly depends on knowing all of these effects. Thus, we introduce CORTEO [3] Monte Carlo simulations to calibrate the efficiency in dependence of matrix composition, sample thickness, depth of origin of a pp-scattering event and detector granularity. The agreement of simulations with measured depth profiles is demonstrated using multilayered sandwich targets.

[1] P. Reichart, et al., Science 306 (2004) 1537.
[2] P. Reichart, et al., Nucl. Instr. and Meth. B197 (2002), pp. 134-149  
[3] F. Schiettekatte, Nucl. Instr. and Meth. B266 (2008), pp. 1880–1885