2:30 PM - 2:45 PM
[MZZ42-03] Development of a method for estimating analytical accuracy considering blooming effects in quantitative imaging using an MCP/FS/qCMOS 2-D ion detection system.
Keywords:SIMS, Isotope Imaging, MCP, qCMOS
Isotopes are useful tracers of chemical and physical processes in materials. In order to combine isotopic composition information with other information such as petrological features and to increase the amount of information, quantitative isotope imaging, which captures isotopes in two dimensions, has been performed mainly by secondary ion mass spectrometry (SIMS). Isotope imaging in SIMS can be performed in two ways: scanning and imaging. The imaging method is effective in increasing the secondary ion intensity for high sensitivity, high accuracy, and short analysis times, while the primary ion intensity can be increased without compromising spatial resolution. In isotope imaging, a highly sensitive two-dimensional detector is required because the ion intensity per detection element is reduced compared to detection in zero dimensions. A system consisting of a microchannel plate (MCP), a fluorescent surface (FS), and a camera has been developed as such a two-dimensional detector (Okano et al. 2024, JpGU; Yoshimoto et al. 2024, Annual Meeting of the Geochemical Society). It has been found empirically that the relationship between the ion count C (Counts Per Second; cps) before amplification and the digital value I (Analog to Digital Unit; ADU) obtained from the image sensor is a characteristic curve, I=pCq (e.g., Mantus and Morrison, 1990). Quantitative analysis by conversion of digital values to ion counts using characteristic curves has hitherto been performed using a single characteristic curve for all camera pixels. However, due to the nature of the MCP/FS/camera system, each channel of the MCP and each pixel of the camera should have a different amplification factor. Okano et al. (2024) evaluated the isotope ratio error for each pixel calculated using the characteristic curve, but the counting statistics error estimated from the secondary ion counts and the isotope distribution estimated from the isotope ratio image did not match, resulting in an apparent increase in accuracy in the MCP/FS/camera system The result was that the apparent accuracy of the MCP/FS/camera system was improved.
In this study, a two-dimensional detection system that enables short-time measurements by using a Hamamatsu Photonics qCMOS camera with extremely low readout noise, a two-stage MCP and a FS capable of short-time attenuation was used. To enable the characteristic curve to be used as a two-dimensional detector while maintaining quantitativity, a pixel-by-pixel method of calculating the characteristic curve was used in this study. The reason for the inaccurate estimation of the error is the in-plane signal blooming caused by the use of the MC P. The MCP/FWS system, such as the one used in the present study, is a two-dimensional detector with an MCP/FWS system. In imaging analyses using MCP/FS/camera systems such as the present system, it is known that electrons from one channel have a Gaussian-like spread between the first and second stages of a two-stage MCP and between the second stage and the FS (e.g., Saito et al. 2007). the blooming effect causes the signal intensity on the camera to be smoothed between several neighboring pixels, reducing the variability and thus underestimating the apparent error. To verify this in this study, the width of the blooming of an ion was determined and the degree of underestimation of the error was estimated by simulation. The sigma value of the two-dimensional Gaussian fitting at blooming was found to be about 2.5 pixels. The degree of underestimation of the error was found to be independent of the exposure time and the intensity of the secondary ions, and the degree of underestimation of the error decreased with larger binning. Using the degree of underestimation of the error calculated by simulation as a correction factor, the repeatability of the imaging analysis was found to be consistent with the counting statistical error. Thus, a method for estimating the true repetition error, considering the influence of the blooming effect, has been successfully developed.
In this study, a two-dimensional detection system that enables short-time measurements by using a Hamamatsu Photonics qCMOS camera with extremely low readout noise, a two-stage MCP and a FS capable of short-time attenuation was used. To enable the characteristic curve to be used as a two-dimensional detector while maintaining quantitativity, a pixel-by-pixel method of calculating the characteristic curve was used in this study. The reason for the inaccurate estimation of the error is the in-plane signal blooming caused by the use of the MC P. The MCP/FWS system, such as the one used in the present study, is a two-dimensional detector with an MCP/FWS system. In imaging analyses using MCP/FS/camera systems such as the present system, it is known that electrons from one channel have a Gaussian-like spread between the first and second stages of a two-stage MCP and between the second stage and the FS (e.g., Saito et al. 2007). the blooming effect causes the signal intensity on the camera to be smoothed between several neighboring pixels, reducing the variability and thus underestimating the apparent error. To verify this in this study, the width of the blooming of an ion was determined and the degree of underestimation of the error was estimated by simulation. The sigma value of the two-dimensional Gaussian fitting at blooming was found to be about 2.5 pixels. The degree of underestimation of the error was found to be independent of the exposure time and the intensity of the secondary ions, and the degree of underestimation of the error decreased with larger binning. Using the degree of underestimation of the error calculated by simulation as a correction factor, the repeatability of the imaging analysis was found to be consistent with the counting statistical error. Thus, a method for estimating the true repetition error, considering the influence of the blooming effect, has been successfully developed.