Target Design in SEM-Based Nano-CT and Its Influence on X-ray Imaging

• Published in: Journal of imaging Vol. 9; no. 8; p. 157
• Main Authors: Fell, Jonas, Wetzler, Felix, Maisl, Michael, Herrmann, Hans-Georg
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.08.2023; MDPI
• Subjects: Aperture; Chemical composition; Chromium; Computed tomography; CT imaging; Design; Diagnostic imaging; Electron beams; Electron microscopy; Electrons; Energy; Energy distribution; Foils; Geometry; Image contrast; Image enhancement; Image processing; Image quality; Influence; Medical imaging; Methods; Monte Carlo simulation; nano-CT; Nanotechnology; Organic materials; Scanning electron microscopy; SEM-based CT; Sensors; Spatial resolution; Spectrum analysis; X ray imagery; X-ray source; X-ray target; X-rays; Germany; United States > US
• ISSN: 2313-433X; 2313-433X
• DOI: 10.3390/jimaging9080157

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.