2,562 research outputs found
Holography and Coherent Diffraction with Low-Energy Electrons: A Route towards Structural Biology at the Single Molecule Level
The current state of the art in structural biology is led by NMR, X-ray
crystallography and TEM investigations. These powerful tools however all rely
on averaging over a large ensemble of molecules. Here, we present an
alternative concept aiming at structural analysis at the single molecule level.
We show that by combining electron holography and coherent diffraction imaging
estimations concerning the phase of the scattered wave become needless as the
phase information is extracted from the data directly and unambiguously.
Performed with low-energy electrons the resolution of this lens-less microscope
is just limited by the De Broglie wavelength of the electron wave and the
numerical aperture, given by detector geometry. In imaging freestanding
graphene, a resolution of 2 Angstrom has been achieved revealing the 660.000
unit cells of the graphene sheet from one data set at once. Applied to
individual biomolecules the method allows for non-destructive imaging and
imports the potential to distinguish between different conformations of
proteins with atomic resolution.Comment: 17 pages, 10 figures; Ultramicroscopy 201
High-Resolution Crystal Truncation Rod Scattering: Application to Ultrathin Layers and Buried Interfaces
In crystalline materials, the presence of surfaces or interfaces gives rise to crystal truncation rods (CTRs) in their X‐ray diffraction patterns. While structural properties related to the bulk of a crystal are contained in the intensity and position of Bragg peaks in X‐ray diffraction, CTRs carry detailed information about the atomic structure at the interface. Developments in synchrotron X‐ray sources, instrumentation, and analysis procedures have made CTR measurements into extremely powerful tools to study atomic reconstructions and relaxations occurring in a wide variety of interfacial systems, with relevance to chemical and electronic functionalities. In this review, an overview of the use of CTRs in the study of atomic structure at interfaces is provided. The basic theory, measurement, and analysis of CTRs are covered and applications from the literature are highlighted. Illustrative examples include studies of complex oxide thin films and multilayers
py4DSTEM: a software package for multimodal analysis of four-dimensional scanning transmission electron microscopy datasets
Scanning transmission electron microscopy (STEM) allows for imaging,
diffraction, and spectroscopy of materials on length scales ranging from
microns to atoms. By using a high-speed, direct electron detector, it is now
possible to record a full 2D image of the diffracted electron beam at each
probe position, typically a 2D grid of probe positions. These 4D-STEM datasets
are rich in information, including signatures of the local structure,
orientation, deformation, electromagnetic fields and other sample-dependent
properties. However, extracting this information requires complex analysis
pipelines, from data wrangling to calibration to analysis to visualization, all
while maintaining robustness against imaging distortions and artifacts. In this
paper, we present py4DSTEM, an analysis toolkit for measuring material
properties from 4D-STEM datasets, written in the Python language and released
with an open source license. We describe the algorithmic steps for dataset
calibration and various 4D-STEM property measurements in detail, and present
results from several experimental datasets. We have also implemented a simple
and universal file format appropriate for electron microscopy data in py4DSTEM,
which uses the open source HDF5 standard. We hope this tool will benefit the
research community, helps to move the developing standards for data and
computational methods in electron microscopy, and invite the community to
contribute to this ongoing, fully open-source project
Three-dimensional double helical DNA structure directly revealed from its X-ray fiber diffraction pattern by iterative phase retrieval
Coherent diffraction imaging (CDI) allows the retrieval of the structure of
an isolated object, such as a macromolecule, from its diffraction pattern. CDI
requires the fulfilment of two conditions: the imaging radiation must be
coherent and the object must be isolated. We discuss that it is possible to
directly retrieve the molecular structure from its diffraction pattern which
was acquired neither with coherent radiation nor from an individual molecule,
provided the molecule exhibits periodicity in one direction, as in the case of
fiber diffraction. We demonstrate that by applying iterative phase retrieval
methods to a fiber diffraction pattern, the repeating unit, that is, the
molecule structure, can directly be reconstructed without any prior modeling.
As an example, we recover the structure of the DNA double helix in
three-dimensions from its two-dimensional X-ray fiber diffraction pattern,
Photograph 51, acquired in the famous experiment by Raymond Gosling and
Rosalind Franklin, at a resolution of 3.4 Angstrom
Phase Retrieval with Application to Optical Imaging
This review article provides a contemporary overview of phase retrieval in
optical imaging, linking the relevant optical physics to the information
processing methods and algorithms. Its purpose is to describe the current state
of the art in this area, identify challenges, and suggest vision and areas
where signal processing methods can have a large impact on optical imaging and
on the world of imaging at large, with applications in a variety of fields
ranging from biology and chemistry to physics and engineering
Investigations in space-related molecular biology
Improved instrumentation and preparation techniques for high resolution, high voltage cryo-electron microscopic and diffraction studies on terrestrial and extraterrestrial specimens are reported. Computer correlated ultrastructural and biochemical work on hydrated and dried cell membranes and related biological systems provided information on membrane organization, ice crystal formation and ordered water, RNA virus linked to cancer, lunar rock samples, and organometallic superconducting compounds. Apollo 11, 12, 14, and 15 specimens were analyze
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