The advent of the X-ray free-electron laser (XFEL) has made it possible to record diffraction snapshots of biological entities injected into the X-ray beam before the onset of radiation damage. ...Algorithmic means must then be used to determine the snapshot orientations and thence the threedimensional structure of the object. Existing Bayesian approaches are limited in reconstruction resolution typically to 1/10 of the object diameter, with the computational expense increasing as the eighth power of the ratio of diameter to resolution. We present an approach capable of exploiting object symmetries to recover three-dimensional structure to high resolution, and thus reconstruct the structure of the satellite tobacco necrosis virus to atomic level. Our approach offers the highest reconstruction resolution for XFEL snapshots to date and provides a potentially powerful alternative route for analysis of data from crystalline and nano-crystalline objects.
The observation of an order-disorder transition in the semiconductor strained-superlattice system GeSi/Si, which doubles the lattice periodicity in a 111 line type direction, is reported. This ...phenomenon may be representative of a class of order-disorder transitions in strained-semiconductor systems, even when the lattice mismatch is small.
We demonstrate two‐dimensional mapping of pn junctions in transistors by electron holography. The source and drain areas in phase images of 0.3 μm CMOS transistors can be delineated with the correct ...sign of the potential change, thus enabling a distinction between NMOS and PMOS devices in TEM holography. Measurements of samples containing abrupt boron marker layers establish a spatial resolution of 5 nm for mapping the electrostatic potential distribution across pn junctions.
Single-particle structure recovery without crystals or radiation damage is a revolutionary possibility offered by X-ray free-electron lasers, but it involves formidable experimental and ...data-analytical challenges. Many of these difficulties were encountered during the development of cryogenic electron microscopy of biological systems. Electron microscopy of biological entities has now reached a spatial resolution of about 0.3 nm, with a rapidly emerging capability to map discrete and continuous conformational changes and the energy landscapes of biomolecular machines. Nonetheless, single-particle imaging by X-ray freeelectron lasers remains important for a range of applications, including the study of large “electron-opaque” objects and time-resolved examination of key biological processes at physiological temperatures. After summarizing the state of the art in the study of structure and conformations by cryogenic electron microscopy, we identify the primary opportunities and challenges facing X-ray-based single-particle approaches, and possible means for circumventing them.
We show that real-space analysis of lattice images in terms of multidimensional vectors rests on a small number of physically significant dimensions, each representing the contribution of a ...characteristic pattern forming a basis vector. In many cases, these basis vectors can be linked to “spatial periodicities”, and expressed in terms of conventional formalisms of dynamical scattering. This provides a link between the more abstract (but convenient) real-space image analysis and the more familiar formalisms of image formation in terms of Bloch waves. Within this framework, the simplest implementations of QUANTITEM and Chemical Mapping may be viewed as limiting cases of a more general approach. This helps delineate the application domain for each. The paper is illustrated by reference to the Al
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Composition mapping at high resolution Schwander, P.; Rau, W‐D.; Ourmazd, A.
Journal of microscopy (Oxford),
April 1998, Letnik:
190, Številka:
1‐2
Journal Article
Recenzirano
HRTEM images are traditionally interpreted by comparing experiment and simulation. However, quantitative agreement between experimental and simulated images is rarely achieved. It is thus highly ...desirable to extract quantitative information from HRTEM lattice images directly, without recourse to simulated images. Such ‘direct’ methods have been used to obtain high‐resolution composition maps from the local information content of HRTEM images. We review the real‐space techniques QUANTITEM and chemical mapping and delineate their application range. Finally, we demonstrate that both methods can be regarded as limiting cases of a more general approach.
Quantitative information may be extracted from local areas of images that consist of one or more types of unit cell. Fourier-space analysis, real-space intensity analysis, and real-space vector ...pattern recognition are discussed. The pattern recognition approach efficiently exploits the available information by representing the intensity distribution within each unit cell of the image as a multidimensional vector. Thus, the amount and the effect of noise present are determined, statistically significant features are identified, and quantitative comparisons are made with model images. In the case of chemical lattice images, the position of a vector can be directly related to the atomic composition of the unit cell it represents, allowing quantitative chemical mapping of materials at near-atomic sensitivity and resolution. More generally, the vector approach allows the efficient and quantitative extraction of information from images, which consist of mosaics of unit cells. The simple pattern recognition procedure we have described shows that lattice images contain a wealth of information, which can be extracted and evaluated quantitatively. Our approach allows efficient exploitation of the data, quantitative assessment of the effect of noise, identification of statistically significant features, and quantitative comparison with templates. In the case of chemical lattice images, the local information content can be directly related to the local composition of the sample, leading to the chemical mapping of materials at the atomic level. In the case of structural lattice images and tunneling micrographs, it should lead to a more quantitative approach to structure determination by microscopic techniques. In images of biological samples, it may allow a quantitative analysis of similarities and differences between different cells or microorganisms.
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