Effect of crystal and beam tilt on simulated high-resolution TEM images of interfaces.

The effects of crystal and beam tilt on high-resolution transmission electron microscope (HRTEM) images of planar coherent interfaces were investigated by multislice image simulations. It was found that a beam tilt of 0.5 Bragg angle (theta B) was sufficient to introduce detrimental artifacts into most images of interfaces in crystals only 1/8 xi 000 thick, while crystal tilt had a much smaller effect even for crystals 1 xi 000 thick. Effects produced in HRTEM images of interfaces by crystal and beam tilt included the introduction of additional periodicities and loss of compositional detail across a boundary, translation of a boundary from its actual position, and apparent mismatch of atomic planes across a perfectly coherent interface. These results indicate that alignment of the electron beam parallel to the optic axis is critical for reliable HRTEM imaging of interfaces in materials. Techniques for obtaining accurate alignment are also discussed.