Examples of BF and DF TEM images
TEM images of ZrO2
Electron diffraction pattern: the spots indicate the presence of single microcrystals. The apertures (red circles) are localized around the direct beam for recording the bright field (BF) image and around a few diffracted beams for the dark field (DF) image. The intense direct beam is blocked by a metal rod (black shadow on the left center) to avoid overexposure.
TEM BF and DF images of the same area of microcrystalline ZrO2. In the BF image (left), some crystals appear with dark contrast since they are oriented (almost) parallel to a zone axis (Bragg contrast). In addition, thickness contrast occurs: areas close to the edge are thinner and thus appear brighter (lower right side) than those far of the edge (upper left side). In the DF image (right), some of the microcrystals appear with bright contrast, namely such whose diffracted beams partly pass the objective aperture.