On projected widths of stacking faults used for foil thickness determinations

Abstract

Abstract Transmission electron microscopy studies of stacking faults in a Co-based alloy show that under some microscopy conditions the width of the bright-field image of a fault is significantly less than the width of the corresponding weak-beam dark-field image, the latter providing a good indication of the true fault width. Further microscopy studies and examination of the equations describing the contrast caused by a stacking fault in a perfect crystal demonstrate that the discrepancy in observed width exists for faults with a negative phase angle α, when the deviation of the foil from the perfect Bragg reflecting position is greater than zero. An additional condition is that the foil thickness must be in the range ξ g ≤t≤2ξ g , where t is the thickness and ξ g the extinction distance. This effect can lead to serious errors in the calculation of foil thickness in materials of low stacking fault energy, where a common method of thickness determination is based upon the projected width of stacking fault...