Black background technique
Darkfield TEM studies of thermoplastics

In the microscopic examination of crystalline samples, whether polymeric or otherwise, the incident electron beam is diffracted into several beams by crystalline planes that are in a suitable orientation to the incident beam, called the Bragg angle. This orientation corresponds to a resonance between crystalline periodicity and electron wavelength. The diffracted beams are eliminated from the image by a contrast diaphragm, so that the parts of the crystal that are oriented at the Bragg angle appear dark in the image, while the empty parts, i.e. the...