Scanning Transmission Electron Microscopy Moiré sampling Geometrical Phase Analysis (STEM Moiré GPA)

Abstract One interest of Scanning Transmission Electron Microscopy (STEM) Moire interferometry is to increase the field of view of the electron micrograph mapping the structural properties of the material analyzed. The field of view extension is based on undersampling the features present in the sample and can be done without loss of information following the Moire sampling recovery theorem. The Moire sampling recovery theorem indeed enables the missing information between the undersampled Moire fringes to be completed reconstructing an oversampled version of the STEM Moire hologram. As STEM Moire interferometry carries all the structural properties of the sample, dedicated characterization methods can be furthermore developed. In the following chapter, the characterization of strain in STEM Moire interferometry is explored. As the phase from the Geometrical Phase Analysis (GPA) method is not distorted by the sampling process, the approach using the GPA method directly on the STEM Moire hologram is favored. From the theoretical description, a novel strain characterization technique, called STEM Moire GPA (SMG), is first presented. The application of SMG and its practical aspects are subsequently detailed on a simple case of study. SMG reveals to be an easy and efficient method mapping the 2D strain field over large field of views up to several microns and is complementary to both Dark Field Electron Holography and Nano Beam Precession Electron Diffraction techniques.