2D strain mapping using scanning transmission electron microscopy Moire interferometry and geometrical phase analysis

摘要

A strain characterization technique based on Moire interferometry in a scanning transmission electron microscope (STEM) and geometrical phase analysis (GPA) method is demonstrated. The deformation field is first captured in a single STEM Moire hologram composed of multiple sets of periodic fringes (Moire patterns) generated from the interference between the periodic scanning grating, fixing the positions of the electron probe on the sample, and the crystal structure. Applying basic principles from sampling theory, the Moire patterns arrangement is then simulated using a STEM electron micrograph reference to convert the experimental STEM Moire hologram into information related to the crystal lattice periodicities. The GPA method is finally applied to extract the 2D relative strain and rotation fields. The STEM Moire interferometry enables the local information to be de-magnified to a large length scale, comparable to what can be achieved in dark-field electron holography. The STEM Moire GPA method thus extends the conventional high-resolution STEM GPA capabilities by providing comparable quantitative 2D strain mapping with a larger field of view (up to a few microns). (C) 2017 Elsevier B.V. All rights reserved.