The Orientation and Position Accuracy of Electron Diffraction

The misorientations existing between subgrainsare of critical importance in understanding the nucleationand growth of recrystallised grains. In this paper itis demonstrated that, because of spherical aberration andfocus error in the objective of a conventional 100 kVelectron microscope, the accuracy of beam direction determinationis a function of the size of the area selected,when this area is small. Various factors arediscussed, and it is shown that for beam direction determinationto within 2° accuracy over the whole unittriangle using a modern 100 kV microscope, that the minimumarea must be greater than 1.5 μm diameter. The implicationsof this on previous conventional SAD deformationtexture studies, where the subgrain size is typically ∼ 2,500 Å, are discussed.