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• A new approach to map crystal orientation and strain in TEM samples is described using trained artificial neural networks. • It uses simulated dynamical electron diffraction intensity as the training dataset. • The method is applied to the analysis of four-dimensional electron diffraction datasets. • High angular resolution at 0.009˚ for orientation mapping and strain sensitivity at 0.04% are demonstrated. Techniques for training artificial neural networks (ANNs) and convolutional neural networks (CNNs) using simulated dynamical electron diffraction patterns are described. The premise is based on the following facts. First, given a suitable crystal structure model and scattering potential, electron diffraction patterns can be simulated accurately using dynamical diffraction theory. Secondly, using simulated diffraction patterns as input, ANNs can be trained for the determination of crystal structural properties, such as crystal orientation and local strain. Further, by applying the trained ANNs to four-dimensional diffraction datasets (4D-DD) collected using the scanning electron nanodiffraction (SEND) or 4D scanning transmission electron microscopy (4D-STEM) techniques, the crystal structural properties can be mapped at high spatial resolution. Here, we demonstrate the ANN-enabled possibilities for the analysis of crystal orientation and strain at high precision and benchmark the performance of ANNs and CNNs by comparing with previous methods. A factor of thirty improvement in angular resolution at 0.009˚ (0.16 mrad) for orientation mapping, sensitivity at 0.04% or less for strain mapping, and improvements in computational performance are demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: Information from imaging and diffraction planes, or real and reciprocal spaces, of transmission electron microscopes (TEM) can be combined using iterative transformation algorithms to reconstruct the complex wave function, to improve image resolution and to remove residual aberrations in the case of aberration corrected TEM. Here, we describe the experimental and computation techniques needed for combining real and reciprocal space information. We demonstrate these techniques by reconstructing the complex wave function of quantum dots and carbon nanotubes beyond the microscope''s resolution limit. [Copyright &y& Elsevier]

Abstract: In this work, we elucidate the regular rule of the symmetry in electron diffraction patterns from helical structures. It is affected by the value of the dominating Bessel function orders for the layer lines and relative orientation of the samples with respect to the electron beam. For Single-Walled Carbon nanotubes (SWCNTs), we use analytic analysis and computer simulations to demonstrate that the 2mm symmetry of the electron diffraction may break down not only from an achiral SWCNT, but also from a chiral SWCNT. Also, the simulation work for B-DNA is presented to corroborate the theoretical analysis. [Copyright &y& Elsevier]

• A dual-space compressive sensing method is developed for the collection and reconstruction of 4D-STEM data at high fidelity. • The approach is tested on the subsampled datasets created from a full 4D-STEM dataset of a nanodevice sample, and demonstrated experimentally using random scan in real-space. • The same reconstruction algorithm can be used for compression of 4D-STEM datasets, leading to a large reduction (100 times or more) in data size, while retaining the fine features of 4D-STEM imaging. Four-dimensional Scanning Transmission Electron Microscopy (4D-STEM) is a powerful technique for high-resolution and high-precision materials characterization at multiple length scales, including the characterization of beam-sensitive materials. However, the field of view of 4D-STEM is relatively small, which in absence of live processing is limited by the data size required for storage. Furthermore, the rectilinear scan approach currently employed in 4D-STEM places a resolution- and signal-dependent dose limit for the study of beam sensitive materials. Improving 4D-STEM data and dose efficiency, by keeping the data size manageable while limiting the amount of electron dose, is thus critical for broader applications. Here we introduce a general method for reconstructing 4D-STEM data with subsampling in both real and reciprocal spaces at high fidelity. The approach is first tested on the subsampled datasets created from a full 4D-STEM dataset, and then demonstrated experimentally using random scan in real-space. The same reconstruction algorithm can also be used for compression of 4D-STEM datasets, leading to a large reduction (100 times or more) in data size, while retaining the fine features of 4D-STEM imaging, for crystalline samples. [ABSTRACT FROM AUTHOR]

• Electron nanodiffraction methods for determination of lattice strain are described and compared. • A weighted 2D reciprocal lattice fitting method is proposed, including error analysis. • Strain mapping resolution of 1 nm and precision of ∼3 × 10‒4 is demonstrated on a Si-based FinFET device. • An optimum strain mapping strategy is suggested based on experiments and simulations. Scanning Electron NanoDiffraction (SEND) is a powerful and versatile technique for lattice strain mapping in nano-devices and nano-materials. The measurement is based on Bragg diffraction from a local crystal volume. However, the resolution and precision of SEND are fundamentally limited by the uncertainty principle and scattering that govern electron diffraction. Here, we propose to measure lattice strain using a focused probe and circular Hough transform to locate the position of non-uniform diffraction disks. Methods for fitting a 2D lattice to the detected disks for strain calculation are described, including error analysis. We demonstrate our technique on a FinFET device for strain mapping at the spatial resolution of 1 nm and strain precision of ∼ 3 × 10 − 4 . Using this and simulations, the experimental parameters involved in data acquisition and analysis are thoroughly investigated to construct an optimum strain mapping strategy using SEND. [ABSTRACT FROM AUTHOR]