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

Electron Bessel beam diffraction for precise and accurate nanoscale strain mapping

“…Transmission electron microscopy (TEM) offers strain measurement with the highest spatial resolution and many methods have been developed or adapted to this purpose. Strain can be measured through convergent beam electron diffraction (CBED), high resolution conventional and scanning TEM imaging (HRTEM and HRSTEM) including Moiré fringe analysis (Moiré fringes appear when using a HRSTEM setup to scan at a lower magnification, due to the low-frequency sampling of the crystal lattice) as well as nano beam electron diffraction (NBED) which can also be performed in conjunction with precession electron diffraction (N-PED) [6][7][8][9][10] . Of these techniques, the best accuracy and precision are offered by nano beam precession electron diffraction with a spatial resolution better than 1nm, a strain sensitivity of σ = 2×10 −4 and an accuracy of ∆ = 1×10 −3 , though it requires additional specialised hardware 11,12 .…”

Moiré Fringe Method via Scanning Transmission Electron Microscopy

“…In this manner, the scanning grid is ensured to be identical for STEM‐MF image and HR‐STEM image, allowing STEM‐MF image to be properly calibrated for strain measurement. The corresponding theory and the detailed procedure are well explained by A. Pofelski et al., [ 21 ] who have also developed a python‐based open software “STEM_Moiré_GPA.” [ 45 ] A demonstration of this approach on AlGaN is shown in Figure 3e–k, where 2D deformation maps are successfully present. Limitations of this approach are also present, including 1) negative influence of scan distortions and sample drift, and 2) calibration error which is strongly dependent on the pixel size calibration, can mislead quantification of strain.…”

“…[ 20 ] Analogous to abovementioned moiré fringe techniques, STEM moiré pattern is produced from the beating between the scanning lattice and the crystal lattice. This method was first proposed in 2010 and stated as “scanning moiré fringes (SMF)” [ 20 ] or “STEM moiré hologram” [ 21,22 ] in literature. To distinguish it from the moiré fringe methods in TEM, STM/SEM, etc., we name it as “STEM moiré fringe” or “STEM‐MF” method in this review.…”

Crystal Lattices Reconstruction from Moiré Aliased Scanning Transmission Electron Microscopy Electron Micrograph

“…1. During the undersampling acquisition, the aliasing artifact transforms each crystalline wave vector (or reflection) to its corresponding Moiré wave vector (or reflection) through the sampling vector [12,13] forming the STEM Moiré hologram in Fig. 1 a).…”