= Diffraction contrast
<Diffraction contrast> is image-intensity variation caused by spatially varying <electron diffraction> conditions. JEOL documents a <silicon> semiconductor-interconnect specimen at $200\,\mathrm{kV}$: its differently oriented <crystals> are imaged in <bright-field transmission electron microscopy> and same-area <dark-field transmission electron microscopy>, alongside an <electron diffraction> pattern. Selecting the marked diffracted beam makes the corresponding <crystal> bright after it was dark. The preparation route, thickness and exposure are not supplied. The changed <objective aperture> selection provides a comparison within one specimen; the readout supports orientation-dependent contrast rather than a map of surface height or <chemical composition>.<Diffraction contrast by JEOL>[Definition and silicon example, panels a–c: 200 kV, same-area comparison and selected diffraction spot]{ref}
This comparison is useful precisely because the material has not been replaced between the two images. It does not prove that thickness and <chemical composition> never influence <transmission electron microscopy contrast>. Instead, it supplies a concrete counterexample to assigning either quantity uniquely from brightness. A proposed extension is to repeat the first aperture setting after the second: recovery of the original contrast tests whether specimen motion or irradiation changed the comparison.
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