As an instrument, the scanning transmission electron microscope is unique in being able to simultaneously explore both local structural and chemical variations in materials at the atomic scale. This is made possible as both types of data are acquired serially, originating simultaneously from sample interactions with a sharply focused electron probe. Unfortunately, such scanned data can be distorted by environmental factors, though recently fast-scanned multi-frame imaging approaches have been shown to mitigate these effects. Here, we demonstrate the same approach but optimized for spectroscopic data; we offer some perspectives on the new potential of multi-frame spectrum-imaging (MFSI) and show how dose-sharing approaches can reduce sample damage, improve crystallographic fidelity, increase data signal-to-noise, or maximize usable field of view. Further, we discuss the potential issue of excessive data-rates in MFSI, and demonstrate a file-compression approach to significantly reduce data storage and transmission burdens.

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.

The differential phase contrast (DPC) imaging in STEM was mainly used for a study of magnetic material in a medium resolution. An ideal DPC signals give the center of mass of the diffraction pattern, which is proportional to an electric field. Recently, the possibility of the DPC imaging at atomic resolution was demonstrated. Thus, the DPC imaging opens up the possibility to observe the object phase that is proportional to the electrostatic potential.In this report we investigate the numerical procedures to obtain the object phase from the two perpendicular DPC signals. Specifically, we demonstrate that the discrete cosine transform (DCT) is the method to solve the Poisson equation, since we can use the Neumann boundary condition directly specified by the DPC signals. Furthermore, based on the fast Fourier transform (FFT) of an extended DPC signal we introduce the scheme that gives an equivalent result that is obtained with the DCT. The results obtained with the DCT and extended FFT method are superior to the results obtained with commonly used FFT. In addition, we develop real-time integration schemes that update the result with the progress of the scan. Our real-time integration gives the reasonable result, and can be used in a view mode. We demonstrate that our numerical procedures work excellently with the experimental DPC signals obtained from SrTiO3 single crystal.

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