An Introduction to High-Voltage Electron Microscopy

The various features of high voltage electron microscopy are examined in some detail, including basic features of the instrument such as lens aberrations, etc and more particularly, the effect of the microscope voltage on the behaviour of crystalline specimens, both in respect of the formation of diffraction contrast from defects and the production of radiation damage. High accelerating voltages (i.e. 500 to 1000 kV) enable thicker foils (1 to 2 mu m of medium atomic number materials and 4 to 8 mu m of aluminium) to be used so that the foil behaviour is more typical of bulk material. In addition, diffraction patterns can be obtained from smaller precipitates and sharp dark field micrographs can be produced without beam tilting. The major disadvantage is probably the formation of radiation damage by displacement of atoms when the electron energy exceeds a threshold value.