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 electr on diffraction, The HOLZ line positions are commonly used to measure the st rain state in the investigated material. Besides the automation, a very imp ortant aspect is the accuracy of the detected line positions. The limits ar e determined by the amount of noise in the pattern relative to the contrast of the HOLZ lints and the line width. Our investigations show that sub-pix el resolution can be achieved routinely. We have also developed a new strai n analysis procedure in which the dynamical shift of each individual line c an 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 ac curacy of the strain analysis. A measurement of the thermal expansion of al uminium is presented as a model experiment, The lattice constants were dete rmined with an accuracy of about 10(-4).