Electron Crystallography of Organic Molecules PDF Download
Are you looking for read ebook online? Search for your book and save it on your Kindle device, PC, phones or tablets. Download Electron Crystallography of Organic Molecules PDF full book. Access full book title Electron Crystallography of Organic Molecules by J.R. Fryer. Download full books in PDF and EPUB format.
Author: J.R. Fryer
Publisher: Springer Science & Business Media
ISBN: 940113278X
Category : Science
Languages : en
Pages : 388
Get Book Here
Book Description
Maximum Entropy (ME) techniques have found widespread applicability in the reconstruction of incomplete or noisy data. These techniques have been applied in many areas of data analysis including imaging, spectroscopy, and scattering [Gull and Skilling, 1984]. The techniques have proven particularly useful in astronomy [Narayan and Nityanada, 1984]. In many of these applications the goal of the reconstruction is the detection of point objects against a noisy background. In this work we investigate the applicability of ME techniques to data sets which have strong components which are periodic in space or time. The specific interest in our laboratory is High Resolution Electron Micrographs of beam sensitive materials. However, ME techniques are of general interest for all types of data. These data mayor may not have a spatial or temporal character. Figure 1 shows an HREM image of the rigid-rod polymer poly(paraphenylene benzobisoxazole) (PBZO). The 0.55 nm spacings in the image correspond to the lateral close-packing between the extended polymer molecules. Near the center of this crystallite there is evidence for an edge dislocation. In HREM images both the frequency and position of the infonnation is important for a proper interpretation. Therefore, it is necessary to consider how image processing affects the fidelity of this information in both real and Fourier space.
Author: J.R. Fryer
Publisher: Springer Science & Business Media
ISBN: 940113278X
Category : Science
Languages : en
Pages : 388
Get Book Here
Book Description
Maximum Entropy (ME) techniques have found widespread applicability in the reconstruction of incomplete or noisy data. These techniques have been applied in many areas of data analysis including imaging, spectroscopy, and scattering [Gull and Skilling, 1984]. The techniques have proven particularly useful in astronomy [Narayan and Nityanada, 1984]. In many of these applications the goal of the reconstruction is the detection of point objects against a noisy background. In this work we investigate the applicability of ME techniques to data sets which have strong components which are periodic in space or time. The specific interest in our laboratory is High Resolution Electron Micrographs of beam sensitive materials. However, ME techniques are of general interest for all types of data. These data mayor may not have a spatial or temporal character. Figure 1 shows an HREM image of the rigid-rod polymer poly(paraphenylene benzobisoxazole) (PBZO). The 0.55 nm spacings in the image correspond to the lateral close-packing between the extended polymer molecules. Near the center of this crystallite there is evidence for an edge dislocation. In HREM images both the frequency and position of the infonnation is important for a proper interpretation. Therefore, it is necessary to consider how image processing affects the fidelity of this information in both real and Fourier space.
Author: D. Dorset
Publisher: Springer Science & Business Media
ISBN: 9401589712
Category : Science
Languages : en
Pages : 447
Get Book Here
Book Description
The re-emergent field of quantitative electron crystallography is described by some of its most eminent practitioners. They describe the theoretical framework for electron scattering, specimen preparation, experimental techniques for optimum data collection, the methodology of structure analysis and refinement, and a range of applications to inorganic materials (including minerals), linear polymers, small organic molecules (including those used in nonlinear optical devices), incommensurately modulated structures (including superconductors), alloys, and integral membrane proteins. The connection between electron crystallography and X-ray crystallography is clearly defined, especially in the utilisation of the latest methods for direct determination of crystallographic phases, as well as the unique role of image analysis of high-resolution electron micrographs for phase determination. Even the aspect of multiple beam dynamic diffraction (once dreaded because it was thought to preclude ab initio analysis) is considered as a beneficial aid for symmetry determination as well as the elucidation of crystallographic phases, and as a criterion for monitoring the progress of structure refinement. Whereas other texts have hitherto preferentially dealt with the analysis of electron diffraction and image data from thin organic materials, this work discusses - with considerable optimism - the prospects of looking at `harder' materials, composed of heavier atoms. Audience: Could be used with profit as a graduate-level course on electron crystallography. Researchers in the area will find a statement of current progress in the field.
Author: Thomas E. Weirich
Publisher: Springer Science & Business Media
ISBN: 1402039204
Category : Science
Languages : en
Pages : 533
Get Book Here
Book Description
During the last decade we have been witness to several exciting achievements in electron crystallography. This includes structural and charge density studies on organic molecules complicated inorganic and metallic materials in the amorphous, nano-, meso- and quasi-crystalline state and also development of new software, tailor-made for the special needs of electron crystallography. Moreover, these developments have been accompanied by a now available new generation of computer controlled electron microscopes equipped with high-coherent field-emission sources, cryo-specimen holders, ultra-fast CCD cameras, imaging plates, energy filters and even correctors for electron optical distortions. Thus, a fast and semi-automatic data acquisition from small sample areas, similar to what we today know from imaging plates diffraction systems in X-ray crystallography, can be envisioned for the very near future. This progress clearly shows that the contribution of electron crystallography is quite unique, as it enables to reveal the intimate structure of samples with high accuracy but on much smaller samples than have ever been investigated by X-ray diffraction. As a tribute to these tremendous recent achievements, this NATO Advanced Study Institute was devoted to the novel approaches of electron crystallography for structure determination of nanosized materials.
Author: D. Dorset
Publisher: Springer
ISBN: 9780792348764
Category : Science
Languages : en
Pages : 464
Get Book Here
Book Description
The re-emergent field of quantitative electron crystallography is described by some of its most eminent practitioners. They describe the theoretical framework for electron scattering, specimen preparation, experimental techniques for optimum data collection, the methodology of structure analysis and refinement, and a range of applications to inorganic materials (including minerals), linear polymers, small organic molecules (including those used in nonlinear optical devices), incommensurately modulated structures (including superconductors), alloys, and integral membrane proteins. The connection between electron crystallography and X-ray crystallography is clearly defined, especially in the utilisation of the latest methods for direct determination of crystallographic phases, as well as the unique role of image analysis of high-resolution electron micrographs for phase determination. Even the aspect of multiple beam dynamic diffraction (once dreaded because it was thought to preclude ab initio analysis) is considered as a beneficial aid for symmetry determination as well as the elucidation of crystallographic phases, and as a criterion for monitoring the progress of structure refinement. Whereas other texts have hitherto preferentially dealt with the analysis of electron diffraction and image data from thin organic materials, this work discusses - with considerable optimism - the prospects of looking at `harder' materials, composed of heavier atoms. Audience: Could be used with profit as a graduate-level course on electron crystallography. Researchers in the area will find a statement of current progress in the field.
Author: Norbert Karl
Publisher: Springer Science & Business Media
ISBN: 3642762530
Category : Science
Languages : en
Pages : 169
Get Book Here
Book Description
Lattice defects of organic molecular crystals affect their optical or electrical properties by changing the local energy structure. Lattice defects also playa very important role in the chemical and physical properties, for example, as an active site of a catalyst or an initiating point of a solid state reaction. However, very little has been reported on the defect structure of real organic crystals. In the past ten years it became clear that the origin and the structure of the defects depend on the geometrical and chemical nature of the building units of the crystal, the molecules. Molecular size, form and anisotropy, charge distribution, etc. cause the characteristic structure of the defect. Accordingly, a defect structure found in one compound may not be found in others. The defect structure of an organic crystal cannot be defined solely by the displacement of the molecular center from the normal lattice site. A rotational displacement of a molecule is frequently accompanied by a parallel shift of the molecular center. In addition to the usual geometrical crystallographic defects, chemical defects are important too which originate, for example, from differences in the substitution sites of molecules carrying side groups. In order to reveal such defect structures, direct imaging of molecules by high resolution electron microscopy is the only direct method.
Author: Edgar A. Silinsh
Publisher: Springer Science & Business Media
ISBN: 3642814646
Category : Science
Languages : en
Pages : 404
Get Book Here
Book Description
This book is based on the results of many years of experimental work by the author and his colleagues, dealing with the electronic properties of organic crystals. E. Silinsh has played a leading role in pOinting out the importance of the polarization energy by an excess carrier, in determining not only the character of the carrier mobility in organic crystals, but in determining the band gap and the nature of the all-important trapping site in these crystals. The one-electron model of electronic conductivity that has been so successful in dealing with inorganic semiconductors is singular ly unsuccessful in rationalizing the unusual physical properties of organic crystals. A many-body theory is required, and the experimental manifestation of this is the central role played by the crystal polarization enerqies in transferring the results obtained with the isolated molecule, to the solid. The careful studies of E. Silinsh in this field have shown tn detail how this polarization energy develops around the excess carrier (and also the hole-electron pair) sitting on a molecular site in the crystal. As with all insulators, trapping sites playa dominant role in reducing the magnitude of ~he current that can theoretically pass through the organic crystal. It is usually the case that these trapping sites are energetically distributed within the forbidden band of the crystal. For many years, an exponential distribution has shown itself to be useful and reasonably correct: However,' E.
Author: David George Howitt
Publisher:
ISBN:
Category : Amines
Languages : en
Pages : 152
Get Book Here
Book Description
Author: Jack D. Dunitz
Publisher: Wiley-VCH
ISBN:
Category : Science
Languages : en
Pages : 520
Get Book Here
Book Description
This book is the second corrected reprint of â2X-Ray Analysisâ2, published in 1979 and consists of two parts. Part one is about Crystal Structure Analysis, part two deals with Molecular Structure. All the information in this volume is of considerable value especially to those engaged in, or about to embark upon, X-ray crystal structure analysis.
Author: D.L. Dorset
Publisher: Springer Science & Business Media
ISBN: 1475766211
Category : Science
Languages : en
Pages : 455
Get Book Here
Book Description
This authoritative text on electron diffraction and crystal structure analysis is the first to describe direct phasing techniques in electron crystallography. Written for electron diffractionists and electron microscopists, this fully illustrated volume presents methods for specimen preparation, data collection and structure analysis. Chapters feature numerous detailed examples of actual structure analyses and contain over 350 illustrations.
Author: Ambarneil Saha
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
Get Book Here
Book Description
This dissertation describes a set of experiments loosely unified under the general theme of 3D electron crystallography. Chapter 1 provides a comprehensive overview of the scientific literature in the field, with particular emphasis on experiments aimed at using electron diffraction to elucidate the atomic structure of three-dimensional molecular crystals. Chapter 2 focuses on the development of a publicly accessible web server, FAES (Factors of Atomic Electron Scattering, httpss://srv.mbi.ucla.edu/faes), containing a database of electron scattering factors parameterized into Gaussian approximations compatible with widely used least-squares refinement programs. These include all neutral and ionic species tabulated in the International Tables for Crystallography, as well as fractionally charged scattering factors calculated by computing linearly weighted sums of adjacent integral neighbors. FAES provides numerical fitting coefficients, statistical goodness-of-fit values, and elastic and estimated inelastic cross-sections at a range of accelerating voltages relevant to transmission electron microscopy. Chapter 3 details rigorous studies involving the mapping of electron beam-induced radiolytic damage in molecular crystals using 4D scanning transmission electron microscopy (4D-STEM), conducted on a variety of organic and organometallic species spanning a wide gamut of chemical space. By acquiring a series of consecutive 4D-STEM scans on the same crystal, we explicitly visualize the spatial evolution of coherently diffracting zones (CDZs) as a function of accumulating electron fluence, providing a detailed, time-resolved map of the internal lattice reorientation induced by radiolysis. These experiments also unveil the resolution-dependent propagation of tides of amorphization from impact craters created by asymmetric, localized delivery of incident electrons. Chapter 4 relates the development of the 4D-STEM method nanobeam electron diffraction tomography into a technique capable of overcoming obstacles that thwart structural elucidation by conventional microcrystal electron diffraction (microED). 4D-STEM's unique ability to pinpoint a specific nanoscale volume for data analysis enables pixel-by-pixel spatial exclusion of unwanted signal from disordered or Bragg-silent regions, empowering us to simply pick and choose whichever CDZs generate the highest-quality diffraction patterns. These experiments represent the first 4D-STEM structures phased ab initio by direct methods.
