Effects of Detector Dead-time on Quantitative Analyses Involving Boron and Multi-Hit Detection Events in Atom Probe Tomography

Abstract

In atom probe tomography (APT), some elements tend to field evaporate preferentially in multi-hit detection events. Boron (B) is one such element. It is thought that a large fraction of the B signal may be lost during data acquisition and is not reported in the mass spectrum or in the 3-D APT reconstruction. Understanding the relationship between the field evaporation behavior of B and the limitations for detecting multi-hit events can provide insight into the signal loss mechanism for B and may suggest ways to improve B detection accuracy. The present work reports data for nominally pure B and for B-doped Si (NIST-SRM2137) at dose levels two-orders of magnitude lower than that which was previously studied by Da Costa, et al. in 2012, while exploring a Fourier based signal processing approach to resolve same isotope, same charge-state ion pair (e.g. 11B1+/11B1+) information in multi-hit detection events. B concentration profiles collected from SRM2137 specimens qualitatively confirmed a signal loss mechanism is 2 at work in atom probe measurements of B in Si. Ion correlation analysis was used to graphically demonstrate that the detector dead-time results in few same isotope, same charge-state ion pairs being properly recorded in the multi-hit data, explaining why B is consistently under-represented in quantitative analyses. Given the important role of detector dead-time as a signal loss mechanism, three different methods for estimating the detector dead-time were presented. The findings of this study, as demonstrated through Si, apply to all quantitative analyses, not just those involving elements that are preferentially detected in multi-hit events.