Electron Diffraction Scattering Research Articles

<b>Basalt waste added to Portland cement

Portland cement is widely used as a building material and more than 4.3 billion tons were produced in 2014, with increasing environmental impacts by this industry, mainly through CO 2 emissions and consumption of non-removable raw materials. Several by-products have been used as raw materials or fuels to reduce environmental impacts. Basaltic waste collected by filters was employed as a mineral mixture to Portland cement and two fractions were tested. The compression strength of mortars was measured after 7 days and Scanning Electron Microscopy (SEM) and Electron Diffraction Scattering (EDS) were carried out on Portland cement paste with the basaltic residue. Gains in compression strength were observed for mixtures containing 2.5 wt.% of basaltic residue. Hydration products observed on surface of basaltic particles show the nucleation effect of mineral mixtures. Clinker substitution by mineral mixtures reduces CO 2 emission per ton of Portland cement.

Characterization of Fine-grained Material Ejected by the Cotopaxi Volcano Employing X-ray Diffraction and Electron Diffraction Scattering Techniques

After 138 years of apparent silence, the Cotopaxi volcano awoke on August 14th of 2015 with a sequence of eruption events and the emission of both fine-grained volcanic material and gases. Four samples of the very first eruption were collected at different sites within the fallout area. The analysis of such samples, by using X-Ray Diffraction (XRD) as well as Electron Diffraction Scattering (EDS) techniques, allow us to determine the geochemical and mineralogical composition. On the basisthe presence of juvenile magma at the proximity of the crater has been categorically excluded. Therefore major eruptions and the subsequent generation of far-reaching lahars can be discarded for the duration of this volcanic stage.

Failure of Friedel's Law in Electron Diffraction Scattering in Bilayer Graphene and Graphene with Defects

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

Studies towards synthesis, evolution and alignment characteristics of dense, millimeter long multiwalled carbon nanotube arrays

We report the synthesis of aligned arrays of millimeter long carbon nanotubes (CNTs), from benzene and ferrocene as the molecular precursor and catalyst respectively, by a one-step chemical vapor deposition technique. The length of the grown CNTs depends on the reaction temperature and increases from ~85 µm to ~1.4 mm when the synthesis temperature is raised from 650 to 1100 °C, while the tube diameter is almost independent of the preparation temperature and is ~80 nm. The parallel arrangement of the CNTs, as well as their tube diameter can be verified spectroscopically by small angle X-ray scattering (SAXS) studies. Based on electron diffraction scattering (EDS) studies of the top and the base of the CNT films, a root growth process can be deduced.

Luminescence Study of Silver Nanoparticles Obtained by Annealed Ionic Exchange Silicate Glasses

The photoluminescence of silver nanoparticles glasses obtained by ionic exchange and annealing is investigated for various ionic exchange times. These glasses are prepared by immersion of silicate glass samples in a molten salt bath of molar concentration 10% AgNO3 in NaNO3 at T = 320 °C. Scanning electron microscopy measurement in electron diffraction scattering (EDS) configuration confirms the silver presence in the various glasses, and the UV/visible absorption gives the evolution of the spectra after ionic exchange and plasmon resonance apparition after annealing. After annealing at 450 °C, both diagnostics inform us about the particles’ formation and the silver rediffusion. Silver nanoparticle growth after annealing prior leads to photoluminescence exaltation and quenching for the longest exchange samples. Subsequently, we propose potential mechanisms of the nanoparticle formation with an initial depolymerization of the silicate network during the ionic exchange and repolymerization during annealing.

Thermal and optical characterization of Zn XCd 1− XS embedded in a zeolite host

Ternary compounds Zn X Cd 1− X S (0≤ X≤1) embedded in mordenite zeolite host are studied by using Photoacoustic techniques and X-ray diffraction. We found the thermal diffusivity, thermal effusivity and band-gap as a function of the X parameter. This study shows a strong dependence of thermal and optical parameters with the X value (Zn% concentration). At low X values, we found a peak in the thermal parameters. From Photoacoustic Spectroscopy (PAS), we observed a parabolic behavior of the band gap as a function of X. The X ray diffraction patterns shows that sintered mordenite host structure was maintained with the growth of the ternary compound, however the intensity of the peaks were sensitive to the X value of these compounds. Electron Diffraction Scattering (EDS) measurements were used to determine the X value of our samples.

Book reviews: Elastic and Inelastic Scattering in Electron Diffraction and Imaging Zhong Lin Wang Plenum Press, New York and London (1995)

Book reviews: Elastic and Inelastic Scattering in Electron Diffraction and Imaging Zhong Lin Wang Plenum Press, New York and London (1995)

Apparent Temperature Factor Due to Dynamical Scattering in Electron Diffraction of Protein Crystals

The failure of the kinematic scattering approximation, and also of the “weak phase object” approximation, may represent one of the most serious problems in the interpretation of high resolution electron diffraction data and electron microscope images. The existence and behavior of dynamical diffraction effects are well characterized in materials science applications, but the possible influence of dynamical effects is still not completely understood in applications involving unstained biological materials, which are characterized by low atomic number and large unit cells. We have previously reported numerical calculations in which we have explored the conditions under which the kinematic approximation would be valid, to an acceptable level of accuracy, for complex biological structures. The known structure of a protein, cytochrome b5, was used as a test object, and the Cowley-Moodie multislice method was used to calculate the “exact” dynamical diffracted waves. For 100 keV electrons it has been found that the kinematic approximation is acceptable up to a specimen thickness of about 150 Å, as judged by the crystallographic “R-value”, by the appearance of the difference Patterson function (for heavy atom derivatives), and by the number of wrong phases that are derived from the dynamical diffraction intensities.

Elimination of Substrate Scattering in Electron Diffraction

Relative intensities of single crystalline electron diffraction spots can be calculated using n-beam dynamical electron diffraction theory. The scattering matrix formulation developed by Sturkey has been applied in this laboratory to calculate the relative intensities of 42 simultaneously diffracted beams from thin gold platelets. The calculations assume normal incidence, parallel entrance and exit surfaces of the crystal, and crystal thickness t. These assumptions severly restrict the experimental techniques which may be used to measure intensities. A suitable technique must hold the crystal normal to the incident beam, allow thickness measurements, and prevent bending. These rather stringent conditions are satisfied by mounting the microcrystal on a substrate. However, a substrate scatters the electron beam and alters the relative intensities being measured. To eliminate substrate scattering and to satisfy most of the above requirements the micro-crystals were studied through holes in the substrate.

Multiple Elastic Scattering in Electron Diffraction by Molecules

Electron diffraction patterns from gas molecules containing heavy atoms can be satisfactorily interpreted in terms of a pseudokinematical theory, in which rigorous atomic scattering amplitudes are used, but the Born approximation is retained for expressing the (molecular) interference between the various atomic contributions. It is shown that the correction brought by the second approximation of the pseudokinematical theory, involving multiple scattering on different atoms, is a smooth function of scattering angle and is therefore unimportant in the study of the oscillating interference term.

Multiple Elastic Scattering in Electron Diffraction by Crystals

In the case of electron diffraction by crystals containing heavy atoms, it is possible to improve the usual kinematical theory by formulating a pseudokinematical theory, which is expressed in terms of rigorous atomic scattering amplitudes rather than their Born-approximation values. A corresponding improvement can be made in the treatment of the problem by the dynamical theory, and consists in taking into account the coupling of a given diffracted beam with not only the incident beam (as is usually done in first approximation) but also with other diffracted beams. The pseudokinematical and dynamical theories are compared for very thin crystals and the conditions under which both give identical results are discussed. In particular, both predict a failure of Friedel's law in the case of acentric crystals.

On the Inelastic Scattering in Electron Diffraction

On the Inelastic Scattering in Electron Diffraction

Secondary Elastic Scattering in Electron Diffraction

Electron diffraction patterns from films of long-chain paraffins show the effects of secondary elastic scattering of electrons in the form of extra spots, groups of spots, arcs of circles, diffuse bands with sharp edges, and forbidden reflections in single-crystal patterns. Examples of such effects are given and analysed to demonstrate their origin in the successive diffraction of electrons from two different single-crystal regions. It is pointed out that many effects recorded in the literature on electron diffraction may be explained in the same way. The modification of the intensities in single-crystal patterns and the appearance of forbidden reflections are treated quantitatively on the basis of secondary diffraction by parallel but non-coherent regions of crystal. Expressions are derived whereby observed intensities may be corrected for secondary scattering when once the scattering efficiency of the crystal has been deduced from the observed intensities of forbidden reflections. The importance of such corrections for purposes of structure analysis is demonstrated in the comparison of two Fourier projections made from a cross-grating pattern of dicetyl (C32H66), one using observed intensities and the other using corrected intensities. Both show clearly the general arrangement of the molecules, but that based on corrected intensities contains much less spurious detail than the other, and gives greater accuracy and a much clearer indication of the positions of the hydrogen atoms