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Backscatter imaging

Backscatter imaging

Backscatter (BSc) imaging is a second imaging modality available in SEM. While SE-imaging reveals the surface topography of our sample, BSc-imaging can provide information as to its composition. Elements with a high atomic number yield more backscatter electrons than elements with a low atomic number and hence appear bright in the image. Imaging a sample in BSc-mode provides therefore a Z-contrast image indicating differences in elemental composition. Samples for BSc-imaging are imaged uncoated or coated with a layer of carbon to improve sample conductivity.

The Verios 460 is equipped with a range of backscatter detectors: the ETD and TLD detectors can be run in both SE-mode or BSc-mode. The CBS (concentric backscatter) detector is a dedicated BSc detector and its concentric segmentation allows to select for electrons scattered by the sample at different angles. The mirror detector (MD) and the In-column detector (ICD) are also dedicated BSc detectors, sitting increasingly high inside the SEM column, and can be used to obtain increasingly ‘pure’ Z-contrast images of material samples. BSc-imaging is frequently used in conjunction with EDX analysis.

 

CNT SE BSc mode
Carbon nanotubes imaged in SE-mode (left) showing their smooth surface topography. The image on the right is an overlay of this SE-image with the BSc image (red) revealing areas of high Z inside the CNTs. EDX showed this to be the iron catalyst used during CNT synthesis (Prof. Slawomir Boncel, Silesian University of Technology, Poland; DOI: 10.1021/acsbiomaterials.6b00197).