Surface decoration for improving the accuracy of displacement measurements by digital image correlation in SEM

In-situ straining experiments and residual stress evaluations by micromachining require accurate measurement of the surface displacement. These can be conveniently achieved by Digital Image Correlation (DIC). Three surface decoration techniques are presented to enhance surface deformation and residual stress measurement capabilities on micron-scale samples within a Scanning Electron Microscope -Focused Ion Beam (SEM-FIB) instrument. They involve the use of yttria-stabilized-zirconia nano particles applied chemically, nano platinum dots applied using FIB, and Focused Electron Beam (FEB) assisted deposition. The three decoration techniques create distinctive, random surface features that can be used with Digital Image Correlation to provide full field maps of surface displacements at high magnifications. A series of experiments using a FEGSEM / FIB demonstrated the effectiveness of the three surface decoration techniques for FEGSEM imaging at magnifications from 2,000x to 60,000x. The resolution of the image correlation is substantially enhanced by the surface decoration, with displacement standard deviations reduced to the 0.005-0.03 pixel range, depending on the patch size used. The implications for displacement measurement at the micro- and nanoscale are discussed and some examples shown.