Lenseless X-ray Nano-Tomography down to 150nm Resolution: On the Quantification of Modulation Transfer and Focal Spot of the Lab-based ntCT System

TL;DR

This paper characterizes the modulation transfer function and focal spot of a lab-based nano-tomography system, achieving a resolution down to 150nm by analyzing contrast visibility and source focus.

Contribution

It provides a detailed quantification of the system's MTF and PSF, including independent measurements of the source's focal spot, demonstrating high-resolution imaging capabilities.

Findings

MTF corresponds to a 250nm FWHM Gaussian PSF at high frequencies

Additional 1μm FWHM Gaussian contribution at lower frequencies

Resolution of 150nm structures confirmed at 3200 linepairs/mm

Abstract

The ntCT nano tomography system is a geometrically magnifying X-ray microscopy system integrating the recent Excillum NanoTube nano-focus X-ray source and a CdTe photon counting detector from Dectris. The system's modulation transfer function (MTF) and corresponding point spread function (PSF) are characterized by analyzing the contrast visibility of periodic structures of a star pattern featuring line width from 150nm to 1.5$\mu$m. The results, which can be attributed to the characteristics of the source spot, are crosschecked by scanning the source's electron focus over an edge of the structured transmission target in order to obtain an independent measurement of its point spread function. For frequencies above 1000 linepairs/mm, the MTF is found to correspond to a Gaussian PSF of 250nm full width at half maximum (FWHM). The lower frequency range down to 340 linepairs/mm shows an additional Gaussian contribution of 1$\mu$m FWHM. The resulting resolution ranges at 3200 linepairs/mm, which is consistent with the visual detectability of the smallest 150nm structures within the imaged star pattern.