Three-dimensional morphometry in scanning electron microscopy: a technique for accurate dimensional and angular measurements of microstructures using stereopaired digitized images and digital image analysis.

A method for accurate dimensional and angular measurements of microstructures analysed in the scanning electron microscope is described. The method considers central and parallel projections and involves (a) digital image acquisition of stereopaired images from the scanning electron microscope's photodisplay, (b) generation of 3D-image representations, (c) setting of measuring points in the digitized stereopaired images, (d) computation of exact space coordinates (x/y/z) from the corresponding point coordinates (xL/yL; xR/yR), (e) determination of distances and angles between consecutive corresponding points using vector equations, and (f) transfer of computed data into spreadsheets of the data analysis software using dynamic data exchange with simultaneous graphical display of the frequency distribution of variables. Measurements performed on specimens with known dimensions (grid with 10 microm wide square meshes, polystyrene beads with 0.33 microm diameter) and angles (synthetic crystals of K(Al,Cr)[SO4], CuSO4.5H2O and NaCl) revealed a high accuracy in dimensional as well as angular measurements (total error 1 +/- 0.5%). In Monte Carlo experiments the overall error was found to depend strongly on the size of the measured structure relative to the size of the measurement field (field width).