BS ISO 25498:2025 - Page 2

Microbeam analysis. Analytical electron microscopy. Selected area electron diffraction analysis using a transmission electron microscope. | Status: Current

1 Scope This document specifies the method for selected area electron diffraction (SAED) analysis using a transmission electron microscope (TEM) to analyse thin crystalline specimens. This document applies to test areas of micrometres and sub-micrometres in size. The minimum diameter of the selected area in a specimen which can be analysed by this method is restricted by the spherical aberration coefficient of the objective lens of the microscope and approaches hundreds of nanometres for a modern TEM. When the size of an analysed specimen area is smaller than the spherical aberration coefficient restriction, this document can also be used for the analysis procedure. However, because of the effect of spherical aberration and deviation of the specimen height position, some of the diffraction information in the pattern can be generated from outside of the area defined by the selected area aperture. In such cases, the use of microdiffraction (nano-beam diffraction) or convergent beam diffraction, where available, can be preferred. This document is applicable to the acquisition of SAED patterns from crystalline specimens, indexing the patterns and calibration of the camera constant.