Target Design in SEM-based Nano-CT and its Influence on X-ray Imaging

Nano‐computed tomography (nano‐CT) based on scanning electron microscopy (SEM) is utilized for multimodal material characterization in one instrument. Since SEM‐based CT uses geometrical magnification, X‐ray targets can be adapted without any further changes to the system. This allows for designing targets with varying geometry and chemical composition to influence the X‐ray focal spot, intensity and energy distribution with the aim to enhance the image quality. In this paper, three different target geometries with a varying volume are presented: bulk, foil and needle target. Based on the analyzed electron beam properties and X‐ray beam path, the influence of the different target designs on X‐ray imaging is investigated. With the obtained information, three targets for different applications are recommended. A platinum (Pt) bulk target tilted by 25° as an optimal combination of high photon flux and spatial resolution is used for fast CT scans and the investigation of high‐absorbing or large sample volumes. To image low‐absorbing materials, e.g., polymers or organic materials, a target material with a characteristic line energy right above the detector energy threshold is recommended. In the case of the observed system, we used a 30° tilted chromium (Cr) target, leading to a higher image contrast. To reach a maximum spatial resolution of about 100 nm, we recommend a tungsten (W) needle target with a tip diameter of about 100 nm.