Dynamical Theory of Neutron Scattering

1996 ◽  
pp. 63-72 ◽  
Author(s):  
Michel Schlenker ◽  
Jean-Pierre Guigay
Keyword(s):  
Neutron Scattering ◽  
Dynamical Theory

Diffuse Neutron Scattering from Surfaces and Interfaces

1994 ◽  
Vol 376 ◽  
Author(s):  
Sunil K. Sinha
Keyword(s):  
Neutron Scattering ◽  
Diffuse Scattering ◽  
Specular Reflection ◽  
Grazing Incidence ◽  
Magnetic Multilayers ◽  
Dynamical Theory ◽  
X Ray ◽  
Specular Scattering ◽  
Surfaces And Interfaces ◽  
Diffuse Neutron

ABSTRACTThe use of neutron scattering as a tool for exploring surfaces and interfaces has become more prevalent over the last several years, mainly due to the increasing popularity of reflectivity techniques, which study specular reflection from single surfaces or multilayers. Due to intensity limitations, the use of off-specular or grazing-incidence neutron scattering techniques has been much less prevalent. In this paper we shall discuss the origins of magnetic off-specular scattering (e.g., as observed in magnetic multilayers) and the origins of anomalies seen in the X-ray or neutron diffuse scattering from multilayers near Bragg reflections in terms of the Dynamical Theory of Scattering.

A new approach for probing matter in periodic nanoconfinements using neutron scattering

2014 ◽  
Vol 47 (4) ◽  
pp. 1367-1373 ◽  
Author(s):  
Rana Ashkar ◽  
Roger Pynn ◽  
Robert Dalgliesh ◽  
Nickolay V. Lavrik ◽  
Ivan I. Kravchenko
Keyword(s):  
Neutron Scattering ◽  
Small Angle ◽  
Diffraction Grating ◽  
Small Angle Neutron Scattering ◽  
Colloidal Particles ◽  
Spin Echo ◽  
Dynamical Theory ◽  
Silica Particles ◽  
New Approach ◽  
Homogenous Distribution

The efficacy of spin-echo small-angle neutron scattering (SESANS) combined with an exact dynamical theory (DT) model in resolving the arrangement of spherical colloidal particles in planar confinements, such as the channels of a rectangular diffraction grating, is reported. SESANS data obtained with a suspension of charge-stabilized 180 nm silica particles in contact with a silicon diffraction grating, with ∼650 nm-wide channels, show clear deviations from the signal expected from a homogenous distribution of the suspension. DT fits to the data indicate that the colloidal particles are almost twice as concentrated in the channels as they are in the neighboring bulk suspension, consistent with a structure in which the particles are arranged in close-packed sheets parallel to the walls of the confining channels.

Comparison of dynamical theory and phase-object approximation for neutron scattering from periodic structures

2011 ◽  
Vol 44 (5) ◽  
pp. 958-965 ◽  
Author(s):  
Rana Ashkar ◽  
V. O. de Haan ◽  
A. A. van Well ◽  
R. Dalgliesh ◽  
J. Plomp ◽  
...  
Keyword(s):  
Neutron Scattering ◽  
Periodic Structures ◽  
Good Description ◽  
Spin Echo ◽  
Diffraction Gratings ◽  
Grazing Incidence ◽  
Dynamical Theory ◽  
Neutron Spin ◽  
Phase Object ◽  
Neutron Spin Echo

Dynamical theory (DT) calculations have been successfully developed to explain neutron spin-echo resolved grazing-incidence scattering from diffraction gratings. The theory, without any adjustable parameters, has been shown in previous publications to accurately reproduce the sensitivity of the spin-echo polarization signal to sample specifications and scattering geometry. The phase-object approximation (POA), which is computationally less demanding than the DT, has also been used to analyze neutron spin-echo polarization data obtained from diffraction gratings. In this paper, POA and DT calculations are compared for neutron scattering from various diffraction gratings in different geometrical settings. POA gives a good description of the data for transmission cases, where the neutron beam is incident at large angles to the average grating surface. However, for the grazing-incidence reflection cases that were studied, the POA does not fit the data using the independently determined dimensions of the measured gratings. On the other hand, the good agreement between dynamical theory and the data from gratings with known profiles paves the way for its use to extract profile information from periodic samples with unknown structures.

Systematic Reflections and the Two Beam Concept of Extinction Distance

1967 ◽  
Vol 25 ◽  
pp. 332-333
Author(s):  
S. S. Sheinin ◽  
C. D. Cann
Keyword(s):  
Dynamical Theory ◽  
Beam Intensity

The effects of systematic reflections on the variation of diffracted beam intensity with depth in a crystal can only be taken into account by using the multi-beam dynamical theory. The results of calculations of this kind, which are presented here, indicate that the intensity profiles obtained are not periodic. Since extinction distance is a concept strictly applicable only when the diffracted beam intensity varies periodically with depth, its use as a parameter in describing multi-beam intensity profiles must be carefully considered.

Microdiffraction Patterns of Small Metallic Particles II; Theoretical Analysis

1982 ◽  
Vol 40 ◽  
pp. 668-669
Author(s):  
A. Gómez ◽  
P. Schabes-Retchkiman ◽  
M. José-Yacamán ◽  
T. Ocaña
Keyword(s):  
Experimental Data ◽  
Electron Diffraction ◽  
Theoretical Analysis ◽  
Size Range ◽  
Dynamical Theory ◽  
Metallic Particles ◽  
Splitting Effect

The splitting effect that is observed in microdiffraction pat-terns of small metallic particles in the size range 50-500 Å can be understood using the dynamical theory of electron diffraction for the case of a crystal containing a finite wedge. For the experimental data we refer to part I of this work in these proceedings.

Spacings and Intensities of Weak-Beam Dark Field Thickness Fringes

1981 ◽  
Vol 39 ◽  
pp. 222-223
Author(s):  
M. Avalos-Borja ◽  
K. Heinemann
Keyword(s):  
Selection Criterion ◽  
Dark Field ◽  
Dynamical Theory ◽  
Bragg Condition ◽  
Weak Beam ◽  
Kinematical Theory ◽  
Equal Thickness

Weak-beam dark field (WBDF) TEM produces narrowly spaced equal-thickness fringes in wedge-shaped crystals. Using non-systematic diffraction conditions, we have shown elsewhere that simple 2-beam kinematical theory (KT) calculations yield average fringe spacings that are for most practical purposes as satisfactorily accurate as the average spacings obtained from optimized multibeam dynamical theory (DT) calculations, As Fig. 1 shows, this result holds for deviations from the Bragg condition as low as 2x10-1 nm-1, and the differences between the results from the two calculational methods become increasingly insignificant for larger excitation errors. (Unless otherwise noted, all results reported here are for gold crystals, using the 200 beam at 100 KV; the DT calculations were made for 74 beams, using the selection criterion D as discussed in ref. [3]).

Towards quantitative simulations of inelastic electron diffraction patterns and images

1992 ◽  
Vol 50 (2) ◽  
pp. 1170-1171
Author(s):  
Z. L. Wang
Keyword(s):  
Phonon Scattering ◽  
Incident Beam ◽  
Dynamical Theory ◽  
Inelastic Electron ◽  
Additional Advantage ◽  
Coupled Equations ◽  
Atomic Vibrations ◽  
Diffraction Patterns ◽  
Primary Advantage ◽  
The One

A new dynamical theory has been developed based on Yoshioka's coupled equations for describing inelastic electron scattering in thin crystals. Compared to existing theories, the primary advantage of this theory is that the incoherent summation of the diffracted intensities contributed by electrons after exciting vast numbers of different excited states has been evaluated before any numerical calculation. An additional advantage is that the phase correlations of atomic vibrations are considered, so that full lattice dynamics can be combined in the phonon scattering calculation. The new theory has been proven to be equivalent to the inelastic multislice theory, and has been applied to calculate energy-filtered diffraction patterns and images formed by phonon, single electron and valence scattered electrons.A calculated diffraction pattern of elastic and phonon scattered electrons for a parallel incident beam case is in agreement with the one observed (Fig. 1), showing thermal diffuse scattering (TDS) streaks and Kikuchi pattern.

A Stationary Solution of High-Energy Electron Reflection (HEER) for An Arbitrary Surface

1990 ◽  
Vol 48 (2) ◽  
pp. 374-375
Author(s):  
YIQUN MA
Keyword(s):  
Stationary Solution ◽  
High Energy ◽  
Bloch Wave ◽  
Dynamical Theory ◽  
High Energy Electron ◽  
Bulk Materials ◽  
Periodic Surface ◽  
Electron Transmission ◽  
Electron Reflection ◽  
Long Time

For a long time, the development of dynamical theory for HEER has been stagnated for several reasons. Although the Bloch wave method is powerful for the understanding of physical insights of electron diffraction, particularly electron transmission diffraction, it is not readily available for the simulation of various surface imperfection in electron reflection diffraction since it is basically a method for bulk materials and perfect surface. When the multislice method due to Cowley & Moodie is used for electron reflection, the “edge effects” stand firmly in the way of reaching a stationary solution for HEER. The multislice method due to Maksym & Beeby is valid only for an 2-D periodic surface.Now, a method for solving stationary solution of HEER for an arbitrary surface is available, which is called the Edge Patching method in Multislice-Only mode (the EPMO method). The analytical basis for this method can be attributed to two important characters of HEER: 1) 2-D dependence of the wave fields and 2) the Picard iteractionlike character of multislice calculation due to Cowley and Moodie in the Bragg case.

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