Scanning transmission electron microscopy forms an image by scanning a focused electron probe across a thin specimen and recording transmitted or scattered electrons at each probe position. The detector's angular range determines which interaction contributes to the recorded brightness.
A detector including the direct beam gives a different image contrast mechanism from an annular detector collecting scattered electrons. High-angle annular dark-field imaging can emphasize composition and mass-thickness differences, but specimen thickness and channeling still affect interpretation. The probe size limits spatial detail, whereas the displayed-to-scanned length ratio sets magnification; increasing the latter cannot sharpen the probe.
An electron microscope that scans a focused probe across an electron-transparent specimen and records transmitted-electron signals at each scan position. Its image magnification is set by the displayed-to-scanned length ratio, separately from angular detector collection.
Detection of transmitted electrons within an angular annulus excluding the direct beam. Contrast can include diffraction, atomic-number and thickness contributions depending on the collection angles.
A scanning transmission electron microscopy mode collecting electrons scattered to sufficiently large angles. It often gives approximately monotonic atomic-number and mass-thickness contrast, with detector angles and multiple scattering still important.
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