STEM moiré analysis for 2D strain measurements

Abstract

A moiré pattern is created in a scanning transmission electron microscope (STEM) when the scan step is close to a crystalline periodicity. Usually, fringes are visible in only one direction, corresponding to a single set of lattice planes, but fringes can be formed in two directions or more. Using an accurate independent calibration, the strains in silicon devices have been determined from the spacing and orientation of one-directional STEM moiré fringes. In this report, we first discuss the origin of the STEM moiré, and then we show how an accurate calibration of the scan step can be obtained from the STEM moiré pattern itself, providing that we know initially only an approximate scan step and the planar spacing. The new calibration scheme also makes the STEM moiré experiments easier, since it can be applied for the moiré where the scan direction is not precisely aligned with the crystalline lattice. Finally, we show how the two-dimensional strain information will be readily extracted from two one-directional moiré patterns using the concept of geometric phase.

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 .…”

Feasibility Study to Evaluate Lattice-Space Changing of a Step-Graded SiGe/Si (110) Using STEM Moiré

“…It is mandatory to adjust the transmission electron microscope to the level that we can see STEM high resolution images, otherwise the STEM moiré cannot be observed. Figure 4(c) using the software sMoiré [14]. Reciprocals of scan spacing, lattice spacing, and moiré spacing are shown in this figure.…”

“…The research group of the University of Yamanashi also reported the experimental results about STEM moiré observation of Ge/Si (100) [13]. HREM Research Inc. and CEMES-CNRS developed an image analysis method to evaluate two dimensional lattice strains from the STEM moiré [14]. In this study, we produced a compositionally step-graded SiGe thin layers onto the Si (110) substrate, observed the STEM moiré, and calculated the slight change of the {111} plane spacing of the SiGe layers.…”

Low dose scanning transmission electron microscopy of organic crystals by scanning moiré fringes

“…In the case of STEM, the scanning of the electron beam across the sample creates an artificial lattice which is used as the reference to form scanning moiré fringes (SMFs). Generally, SMFs have been used to analyse large area strain measurements in semiconductors and functional oxides [31,34,35,36,37,38]. Additionally, Xray and core energy loss elemental images of the atomic structure of aquamarine, a beam sensitive mineral, have also been recorded using SMFs [39,40].…”