252 research outputs found
A Streaming Multi-GPU Implementation of Image Simulation Algorithms for Scanning Transmission Electron Microscopy
Simulation of atomic resolution image formation in scanning transmission
electron microscopy can require significant computation times using traditional
methods. A recently developed method, termed plane-wave reciprocal-space
interpolated scattering matrix (PRISM), demonstrates potential for significant
acceleration of such simulations with negligible loss of accuracy. Here we
present a software package called Prismatic for parallelized simulation of
image formation in scanning transmission electron microscopy (STEM) using both
the PRISM and multislice methods. By distributing the workload between multiple
CUDA-enabled GPUs and multicore processors, accelerations as high as 1000x for
PRISM and 30x for multislice are achieved relative to traditional multislice
implementations using a single 4-GPU machine. We demonstrate a potentially
important application of Prismatic, using it to compute images for atomic
electron tomography at sufficient speeds to include in the reconstruction
pipeline. Prismatic is freely available both as an open-source CUDA/C++ package
with a graphical user interface and as a Python package, PyPrismatic
A method for crystallographic mapping of an alpha-beta titanium alloy with nanometre resolution using scanning precession electron diffraction and open-source software libraries
An approach for the crystallographic mapping of two-phase alloys on the
nanoscale using a combination of scanned precession electron diffraction and
open source python libraries is introduced in this paper. This method is
demonstrated using the example of a two-phase alpha / beta titanium alloy. The
data was recorded using a direct electron detector to collect the patterns, and
recently developed algorithms to then perform automated indexing and to analyse
the crystallography from the results. Very high-quality mapping is achieved at
a 3nm step size. The results show the expected Burgers orientation
relationships between the alpha laths and beta matrix, as well as the expected
misorientations between alpha laths. It is found that 180{\deg} ambiguities in
indexing occur due to acquisition having been performed too close to a high
symmetry zone axis of the beta with 2-fold projection symmetry (not present in
3D) in the Zero Order Laue Zone for some patterns and that this should be
avoided in data acquisition in the future. Nevertheless, this study
demonstrates a good workflow for the analysis of nanocrystalline two-phase or
multiphase materials, which will be of widespread use in analysing two-phase
titanium and other systems and how they evolve as a function of
thermomechanical treatments.Comment: Submitted to Journal of Microscop
Structure retrieval at atomic resolution in the presence of multiple scattering of the electron probe
The projected electrostatic potential of a thick crystal is reconstructed at
atomic-resolution from experimental scanning transmission electron microscopy
data recorded using a new generation fast- readout electron camera. This
practical and deterministic inversion of the equations encapsulating multiple
scattering that were written down by Bethe in 1928 removes the restriction of
established methods to ultrathin ( {\AA}) samples. Instruments
already coming on-line can overcome the remaining resolution-limiting effects
in this method due to finite probe-forming aperture size, spatial incoherence
and residual lens aberrations.Comment: 6 pages, 3 figure
Patterned probes for high precision 4D-STEM bragg measurements.
Nanoscale strain mapping by four-dimensional scanning transmission electron microscopy (4D-STEM) relies on determining the precise locations of Bragg-scattered electrons in a sequence of diffraction patterns, a task which is complicated by dynamical scattering, inelastic scattering, and shot noise. These features hinder accurate automated computational detection and position measurement of the diffracted disks, limiting the precision of measurements of local deformation. Here, we investigate the use of patterned probes to improve the precision of strain mapping. We imprint a "bullseye" pattern onto the probe, by using a binary mask in the probe-forming aperture, to improve the robustness of the peak finding algorithm to intensity modulations inside the diffracted disks. We show that this imprinting leads to substantially improved strain-mapping precision at the expense of a slight decrease in spatial resolution. In experiments on an unstrained silicon reference sample, we observe an improvement in strain measurement precision from 2.7% of the reciprocal lattice vectors with standard probes to 0.3% using bullseye probes for a thin sample, and an improvement from 4.7% to 0.8% for a thick sample. We also use multislice simulations to explore how sample thickness and electron dose limit the attainable accuracy and precision for 4D-STEM strain measurements
Multislice Electron Tomography using 4D-STEM
Electron tomography offers important three-dimensional (3D) structural
information which cannot be observed by two-dimensional imaging. By combining
annular dark field scanning transmission electron microscopy (ADF-STEM) with
aberration correction, the resolution of electron tomography has reached atomic
resolution. However, tomography based on ADF-STEM inherently suffers from
several issues, including a high electron dose requirement, poor contrast for
light elements, and artifacts from image contrast nonlinearity. Here, we
developed a new method called MultiSlice Electron Tomography (MSET) based on
4D-STEM tilt series. Our simulations show that multislice-based 3D
reconstruction can effectively reduce undesirable reconstruction artifacts from
the nonlinear contrast, allowing precise determination of atomic structures
with improved sensitivity for low-Z elements, at considerably low electron dose
conditions. We expect that the MSET method can be applied to a wide variety of
materials, including radiation-sensitive samples and materials containing light
elements whose 3D atomic structures have never been fully elucidated due to
electron dose limitations or nonlinear imaging contrast.Comment: 26 pages, 9 figure
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