Image and Diffraction Pattern Rotations in the TEM

Abstract

When electrons pass through the electromagnetic lenses in a transmission electron microscope (TEM), they follow a spiral path that results in image rotation. In many TEMs, the image or diffraction pattern that appears at the final imaging plane has therefore suffered a significant rotation compared to the actual specimen. The extent of the rotation is equal to the sum of the contributions from each lens. In some recent instruments an extra lens is built into the column to compensate for these rotations. In the case of a scanning TEM (STEM), where the image is created by scanning a focused beam on the specimen, the orientation of the image to the specimen is fixed but can be controlled electronically by the computer processor.