scholarly journals Accurate Determination of Structure Factors by Pendellosung Methods Using White Radiation

1988 ◽  
Vol 41 (3) ◽  
pp. 433 ◽  
Author(s):  
T Takama ◽  
S Sato
Keyword(s):  
Single Crystal ◽  
Accurate Determination ◽  
Diffraction Theory ◽  
Specimen Thickness ◽  
Dynamical Diffraction ◽  
Laue Spot ◽  
Exit Surface ◽  
Structure Factors ◽  
Integrated Intensity

This paper describes two experimental techniques measuring the Pendellosung beats using white radiation, developed in the authors' laboratory. The intensity of a Laue spot diffracted from a parallel-sided single crystal is successively measured at different Bragg angles, i.e. with different wavelengths. The values of structure factors are evaluated from extremum positions in the measured beats on the basis of the dynamical diffraction theory. In the first method, the integrated intensity diffracted from the whole exit surface is measured, and in the second, the measurement is made only at the centre of the Borrmann fan on the exit surface of a specimen. A discussion is given on the accuracy associated with the following origins of errors: (1) polarisation of incident white radiation, (2) measurement of specimen thickness, (3) measurement of wavelength, (4) determination of extremum positions, and (5) effect of defects in the crystal.

Determination of Mean Free Path for Inelastic Scattering in Poly(2-Vinyl Pyridine) by Low-Loss Spectrum Imaging

2000 ◽  
Vol 6 (S2) ◽  
pp. 224-225
Author(s):  
A. Aitouchen ◽  
T. Chou ◽  
M. Libera ◽  
M. Misra
Keyword(s):  
Free Path ◽  
Free Fall ◽  
Mean Free Path ◽  
Specimen Thickness ◽  
Thickness Determination ◽  
Vinyl Pyridine ◽  
Integrated Intensity ◽  
Inelastic Mean Free Path ◽  
Electron Energy Loss

The common experimental method to determine the total inelastic mean free path i by electron energy-loss spectroscopy (EELS) is by the relation : t/λi= ln(It/IO) [1] where t is the specimen thickness, It, is the total integrated intensity, and Io is the intensity of the zero-loss peak. The accuracy of this measurement depends on the thickness determination. Model geometries like cubes, wedges, and spheres enable accurate thickness determination from transmission images.Spherical polymers with diameters of order 10-200nm can be made from a number of high-Tg polymers by solvent atomization. This research studied atomized spheres of poly(2-vinyl pyridine) [PVP]. A solution of 0.1% PVP in THF was nebulized. After solvent evaporation during free fall within the chamber atmosphere, solid spherical polymer particles with a range of diameters were collected on holey-carbon TEM grids at the bottom of the atomization chamber.

scholarly journals Radiation attenuation by single-crystal diamond windows

2017 ◽  
Vol 50 (1) ◽  
pp. 76-86 ◽  
Author(s):  
M. Guthrie ◽  
C. G. Pruteanu ◽  
M.-E. Donnelly ◽  
J. J. Molaison ◽  
A. M. dos Santos ◽  
...  
Keyword(s):  
Single Crystal ◽  
Accurate Determination ◽  
Incident Beam ◽  
Neutron Radiation ◽  
Cost Effective ◽  
High Pressure Studies ◽  
Single Crystal Diamond ◽  
Diamond Anvil ◽  
Semi Empirical

As artificial diamond becomes more cost effective it is likely to see increasing use as a window for sample environment equipment used in diffraction experiments. Such windows are particularly useful as they exhibit exceptional mechanical properties in addition to being highly transparent to both X-ray and neutron radiation. A key application is in high-pressure studies, where diamond anvil cells (DACs) are used to access extreme sample conditions. However, despite their utility, an important consideration when using single-crystal diamond windows is their interaction with the incident beam. In particular, the Bragg condition will be satisfied for specific angles and wavelengths, leading to the appearance of diamond Bragg spots on the diffraction detectors but also, unavoidably, to loss of transmitted intensity of the beam that interacts with the sample. This effect can be particularly significant for energy-dispersive measurements, for example, in time-of-flight neutron diffraction work using DACs. This article presents a semi-empirical approach that can be used to correct for this effect, which is a prerequisite for the accurate determination of diffraction intensities.

Relation Between the Chemical Short-Range Order in Liquid and Amorphous Alloys

1981 ◽  
Vol 8 ◽  
Author(s):  
C.N.J. Wagneri ◽  
H. Ruppersberg
Keyword(s):  
Amorphous Alloys ◽  
Short Range ◽  
Short Range Order ◽  
Nearest Neighbor ◽  
Diffraction Theory ◽  
Range Order ◽  
Glassy Alloys ◽  
Structure Factors ◽  
Partial Interference

ABSTRACTRecent advances in both diffraction theory and experiment have led to the determination of the topological and chemical short-range order in liquid alloys and metallic glasses. In binary alloys, three partial interference functions (or partial structure factors) must be determined to evaluate the Warren chemical short-range order parameter α. Examples of recent attempts to determine α in binary liquid and glassy alloys are given. In most glasses, studied so far, evidence exists for the occurrence of unlike nearest neighbor ordering which must be present in the liquid state.

scholarly journals Concerning Single Crystal Reflectivity Curves

1988 ◽  
Vol 41 (3) ◽  
pp. 393
Author(s):  
A McL Mathieson
Keyword(s):  
Single Crystal ◽  
Experimental Evidence ◽  
Structure Factor ◽  
Bragg Reflection ◽  
Half Maximum ◽  
Reflectivity Curve ◽  
One Dimensional ◽  
Structure Factors ◽  
Kinematical Limit

The extinguished reflectivity curve of a Bragg single crystal reflection represents the basic experimental evidence for the determination of accurate structure factors. In normal measurement procedures of one-dimensional (ID) 'counter' profiles, information on such curves is obscured by the presence of other, more dominant components. It is therefore difficult to separate out these curves so that a realistic correction for extinction can be applied. By considering the 'shape' of a Bragg reflection in the plane of diffraction from the ~w, ~2e viewpoint, procedures have been deduced for practical zero wavelength dispersion measurement of reflectivity curves for virtually any e value and, with these curves, corrections can be applied to produce extinction-free structure factor values. Attention is drawn to the fact that the width of the experimental reflectivity curve (say at half maximum) can provide a valuable criterion to assist in attaining the 'kinematical limit'.

scholarly journals Determination of Structure Factors by the Pendellosung Effect for Imperfect Crystals

1988 ◽  
Vol 41 (3) ◽  
pp. 519
Author(s):  
NM Olekhnovich
Keyword(s):  
Tilt Angle ◽  
Oscillation Period ◽  
Waller Factor ◽  
X Ray ◽  
Method Of Determination ◽  
Debye Waller Factor ◽  
Structure Factors ◽  
Integrated Intensity ◽  
Coulomb Type

An investigation of thickness dependence of the X-ray integrated intensity of monochromatic linearly polarised X-ray radiation in a symmetrical Laue-case diffraction reveals that the method of determination of structure factors f from thickness oscillations can be extended to real crystals with a static distribution of Coulomb-type defects or dislocations. The f E value (where E is the static Debye-Waller factor) is determined from the oscillation period, while E is determined from the tilt-angle tangent of the oscillation axis of the reduced integrated intensity.

Multiple plasmon scattering contributions to CBED contrast

1995 ◽  
Vol 53 ◽  
pp. 132-133
Author(s):  
Knut Marthinsen ◽  
Ragnvald Høier ◽  
Randi Holmestad
Keyword(s):  
Accurate Determination ◽  
Convergent Beam Electron Diffraction ◽  
Theoretical Description ◽  
Order Structure ◽  
Beam Electron ◽  
Charge Densities ◽  
Energy Filtering ◽  
Structure Factors ◽  
Convergent Beam

One of the most successful applications of quantitative convergent beam electron diffraction (CBED) which have developed over the last years are methods for accurate determination of low-order structure factors. Obvious applications are determination of electron charge densities and bonding effects. However, the use of these methods is still not straight forward, and they are demanding and expensive both experimenatlly and computationally. The experiments have in general to be based on digital intensity recording and energy filtering for partly removing the background of inelastically scattered electrons. Computationally the methods are based on multi-parameter least squares fitting between experiment and theory, and since the complexity of the problem is O(n3), where n is the number of beams included in the calculations, one of the central problems here is to limit n without loss of accuracy. The present work is focused on a theoretical description of the multiple inelastic scattering contributions, in particular plasmon scattering contributions, to CBED contrast.

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