Development of Quantitative Stigmatic SIMS Imaging through Electron-Blooming Correction and Pixel-Wise Ion–Photon Response Calibration

Quantitative ion imaging by secondary ion mass spectrometry (SIMS) is increasingly required for interpreting isotopic and elemental heterogeneities in natural and engineered materials. Previous studies demonstrated the potential of quantitative ion imaging using microchannel plate (MCP), fluorescent screen (FS), and camera-based detection systems [1,2]. However, spatial non-uniformity of detector response and lateral charge-cloud spreading in MCP detectors remain important limitations for fully quantitative imaging [3].

              In this study, we developed a quantitative stigmatic SIMS imaging framework based on an MCP/FS/qCMOS detector system. Single-ion measurements revealed that electron blooming can be approximated by a two-dimensional Gaussian distribution with a characteristic width of approximately 2.65 pixels. Based on this experimentally determined spreading function, an analytical model was derived to evaluate the influence of blooming on Poisson statistics after spatial binning.

            We demonstrate that electron blooming suppresses image variance, resulting in systematic underestimation of statistical uncertainties. To compensate for this effect, an Error Correction Factor (ECF) was derived analytically and validated through numerical simulations. The ECF was found to depend only on binning size and to be independent of signal intensity, enabling practical correction of statistical errors under a wide range of acquisition conditions.

            To correct spatial non-uniformity of detector response, pixel-wise ion–photon response calibration was performed using measurements acquired at multiple ion-intensity levels. Characteristic curves relating digital intensity (ADU s⁻¹) to ion count rate (cps pixel⁻¹) were independently determined for each pixel. The resulting calibration enables direct conversion of detector output into quantitative ion-count distributions while accounting for detector-response variations across the imaging field.

            The combination of electron-blooming correction and pixel-wise calibration establishes a practical methodology for quantitative stigmatic SIMS imaging and quantitative isotope imaging. The developed framework is expected to improve the reliability of quantitative SIMS imaging in geochemistry, cosmochemistry, and materials science.

 

References.

[1] Ion image detection with a microchannel plate evaluated by using a charge coupled device camera, D.S. Mantus, G.H. Morrison, Anal. Chem. 62 (1990) 1148–1155.

[2] High dynamic range quantitative image depth profiling of boron in patterned silicon dioxide on silicon, J.L. Hunter, R.W. Linton, D.P. Griffis, J. Vac. Sci. Technol. A 9 (1991) 1622–1629.

[3] Spatial charge cloud size of microchannel plates, M. Saito, Y. Saito, K. Asamura, T. Mukai, Rev. Sci. Instrum. 78 (2007) 023302.