SPECTROSCOPY
Backscattered Electron and X-ray (BEX) imaging
Exploring techniques that provide detailed information on sample topography
T
he most common modality used in scanning electron microscopy (SEM) is secondary electron (SE)
imaging, which detects lower energy electrons emitted from the sample surface owing to interactions with the SEM electron beam. SE imaging provides information about sample topography. Backscattered electron (BSE)
imaging, on the other hand, detects higher energy electrons scattered back from deeper within the sample. BSE imaging reveals sample composition by atomic number contrast with heavier elements appearing brighter. BEX imaging combines BSE sensors
with X-ray sensors placed below the objective lens. The X-ray detectors collect characteristic X-ray emissions that are generated by the sample when irradiated by the SEM electron beam. The X-ray signal is processed to identify and assign colours to the detected elements, which are then combined with the BSE signal to create a fi nal image. BEX imaging provides more information about sample composition and elemental distribution in the same acquisition time as SE or BSE imaging. Compared with an Energy
Dispersive Spectroscopy (EDS) 24
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Figure 1: The Oxford Instruments remote demo for Bex imaging at the vEM Technology Forum 2024
detector, a BEX imaging system off ers a higher solid angle, enabling X-ray information collection at normal imaging speeds. The position of the X-ray sensors near the objective lens eliminates shadowing eff ects and allows for sample investigation at various working distances. The Unity detector, recognised as
one of the top microscopy innovations of 2024 by the Microscopy Today Innovation Awards, combines two types of sensors within a single detector head. It integrates
backscattered electron (BSE) sensors and X-ray sensors to provide comprehensive imaging with atomic number and elemental data. The detector is designed for daily imaging, off ering fl exibility in working distance, the ability to capture data from challenging sample topography, a wide fi eld of view, and compatibility with variable pressure mode for non-conductive samples. The Unity detector delivers reliable and instant imaging results supported by advanced technology and software integration.
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