Using the Hough transform for HOLZ line identification in convergent beam electron diffraction

The Hough transform as a means for automatic line detection is applied for higher order Laue zone (HOLZ) line identification in convergent beam electron diffraction. The HOLZ line positions are commonly used to measure the strain state in the investigated material. Besides the automation, a very important aspect is the accuracy of the detected line positions. The limits are determined by the amount of noise in the pattern relative to the contrast of the HOLZ lines and the line width. Our investigations show that sub-pixel resolution can be achieved routinely. We have also developed a new strain analysis procedure in which the dynamical shift of each individual line can be taken into account using a model based on several Ewald spheres with different radii. In comparison to the effective high voltage method, finer details of the dispersion surface can be considered, which increases the accuracy of the strain analysis. A measurement of the thermal expansion of aluminium is presented as a model experiment. The lattice constants were determined with an accuracy of about 10⁻⁴.     

Comparison of convergent beam electron diffraction and geometric phase analysis for strain measurement in a strained silicon device

Convergent beam electron diffraction and geometric phase analysis were used to measure strain in the gate channel of a p-type strained silicon metal-oxide-semiconductor field-effect transistor. These measurements were made on exactly the same transmission electron microscopy specimen allowing for direct comparison of the relative advantages of each technique. The trends in the strain values show good agreement in both the [110] and [001] directions, but the absolute strain values are offset from each other. This difference in the absolute strain measured using the two techniques is attributed to the way the reference strain is defined for each.