Model-independent inversion of x-ray or neutron reflectivity data

2001 ◽  
Vol 63 (19) ◽  
Author(s):  
Erman Bengu ◽  
Monica Salud ◽  
L. D. Marks
Keyword(s):  
Neutron Reflectivity ◽  
X Ray ◽  
Model Independent ◽  
Reflectivity Data

The Phase of Scattering Profiles & X-Ray/Neutron Reflectivity

1994 ◽  
Vol 376 ◽  
Author(s):  
P.S. Pershan
Keyword(s):  
Critical Angle ◽  
Scattering Amplitude ◽  
Surface Scattering ◽  
Neutron Reflectivity ◽  
Phase Problem ◽  
X Ray Diffraction ◽  
Phase Information ◽  
X Ray ◽  
Reflectivity Data ◽  
Amplitude Density

ABSTRACTThe phase problem that troubles x-ray diffraction is also a problem for x-ray and neutron reflectivity; however, there are a range of small angles just beyond the critical angle for which the reflectivity contains information on the phase of the surface scattering amplitude. In principle this phase information can be used to determine the asymmetry of the normal gradient of the scattering amplitude density. We discuss here practical conditions under which this symmetry can, or cannot, be extracted from reflectivity data.

Stochastic fitting of specular X-ray reflectivity data usingStochFit

2008 ◽  
Vol 41 (6) ◽  
pp. 1187-1193 ◽  
Author(s):  
Stephen M. Danauskas ◽  
Dongxu Li ◽  
Mati Meron ◽  
Binhua Lin ◽  
Ka Yee C. Lee
Keyword(s):  
Density Distribution ◽  
Electron Density ◽  
Density Profile ◽  
Electron Density Distribution ◽  
Experimental System ◽  
Electron Density Profile ◽  
Physical Parameters ◽  
X Ray ◽  
Model Independent ◽  
Reflectivity Data

Specular X-ray reflectivity data provide detailed information on the electron density distribution at an interface. Typical modeling methods involve choosing a generic electron density distribution based on an initial speculation of the electron density profile from the physical parameters of the experimental system. This can lead to a biased set of solutions.StochFitprovides stochastic model-independent and model-dependent methods for analyzing X-ray reflectivities of thin films at an interface.StochFitdivides an electron density profile into many small boxes and stochastically varies the electron density of these boxes to locate the best fit to a measured reflectivity. Additionally, it provides the ability to perform model-dependent fitting with a stochastic search of the parameter space in order to locate the best possible fit. While model-independent profile search algorithms have been described previously, they are difficult to implement because of the heavy computational requirements, and there is a dearth of software available to the general scientific public utilizing these techniques. Several cases that illustrate the usefulness of these techniques are presented, with a demonstration of how they can be used in tandem.

GenX: an extensible X-ray reflectivity refinement program utilizing differential evolution

2007 ◽  
Vol 40 (6) ◽  
pp. 1174-1178 ◽  
Author(s):  
Matts Björck ◽  
Gabriella Andersson
Keyword(s):  
Differential Evolution ◽  
Recursion Formula ◽  
Differential Evolution Algorithm ◽  
Neutron Reflectivity ◽  
Data Sets ◽  
Local Minima ◽  
X Ray ◽  
Specular Reflectivity ◽  
Evolution Algorithm ◽  
Reflectivity Data

GenXis a versatile program using the differential evolution algorithm for fitting X-ray and neutron reflectivity data. It utilizes the Parratt recursion formula for simulating specular reflectivity. The program is easily extensible, allowing users to incorporate their own models into the program. This can be useful for fitting data from other scattering experiments, or for any other minimization problem which has a large number of input parameters and/or contains many local minima, where the differential evolution algorithm is suitable. In addition,GenXmanages to fit an arbitrary number of data sets simultaneously. The program is released under the GNU General Public License.

REFLEX: a program for the analysis of specular X-ray and neutron reflectivity data

2019 ◽  
Vol 52 (1) ◽  
pp. 201-213 ◽  
Author(s):  
Guillaume Vignaud ◽  
Alain Gibaud
Keyword(s):  
Physical Properties ◽  
Density Profile ◽  
Scattering Length ◽  
Electron Density Profile ◽  
Neutron Reflectivity ◽  
X Rays ◽  
X Ray ◽  
Spin Polarized ◽  
Reflectivity Data ◽  
Footprint Effect

The use of X-ray and neutron reflectivity has been generalized worldwide for scientists who want to determine specific physical properties (such as electron-density profile, scattering-length density, roughness and thickness) of films less than 200 nm thick deposited on a substrate. This paper describes a freeware program named REFLEX, which is a standalone program dedicated to the simulation and analysis of X-ray and neutron reflectivity from multilayers. This program was first written two decades ago and has been constantly improved since, but never published until now. The latest version of REFLEX covers generalized types of calculation of reflectivity curves including both neutron and X-ray reflectivity. In the case of X-rays, the program can deal with both s and p polarization, which is quite important in the soft X-ray region where the two polarizations can yield different results. Neutron reflectivity is calculated within the framework of non-spin-polarized neutrons. REFLEX has also been designed to include any type of fluid (such as supercritical CO2) on top of the analysed film and includes corrections of the footprint effect for analysis on an absolute scale.

scholarly journals A radio parallax to the black hole X-ray binary MAXI J1820+070

2020 ◽  
Vol 493 (1) ◽  
pp. L81-L86 ◽  
Author(s):  
P Atri ◽  
J C A Miller-Jones ◽  
A Bahramian ◽  
R M Plotkin ◽  
A T Deller ◽  
...  
Keyword(s):  
Black Hole ◽  
Inclination Angle ◽  
Precise Measurement ◽  
Very Long Baseline Interferometry ◽  
X Ray ◽  
Long Baseline ◽  
Model Independent ◽  
Jet Velocity ◽  
Very Long Baseline Array

ABSTRACT Using the Very Long Baseline Array and the European Very Long Baseline Interferometry Network, we have made a precise measurement of the radio parallax of the black hole X-ray binary MAXI J1820+070, providing a model-independent distance to the source. Our parallax measurement of (0.348 ± 0.033) mas for MAXI J1820+070 translates to a distance of (2.96 ± 0.33) kpc. This distance implies that the source reached (15 ± 3) per cent of the Eddington luminosity at the peak of its outburst. Further, we use this distance to refine previous estimates of the jet inclination angle, jet velocity, and the mass of the black hole in MAXI J1820+070 to be (63 ± 3)°, (0.89 ± 0.09) c, and (9.2 ± 1.3) M⊙, respectively.

scholarly journals Model-Independent X-Ray Scattering Study of a Silica Sol Surface

JETP Letters ◽  
2018 ◽  
Vol 107 (6) ◽  
pp. 384-389 ◽  
Author(s):  
A. M. Tikhonov ◽  
V. E. Asadchikov ◽  
Yu. O. Volkov ◽  
B. S. Roshchin ◽  
V. Honkimäki ◽  
...  
Keyword(s):  
Silica Sol ◽  
X Ray ◽  
X Ray Scattering ◽  
Scattering Study ◽  
Model Independent ◽  
Ray Scattering

Structural Properties Of Co/Re Superlattices

1991 ◽  
Vol 238 ◽  
Author(s):  
Y. Huai ◽  
R. W. Cochrane ◽  
Y. Shi ◽  
H. E. Fischer ◽  
M. Sutton
Keyword(s):  
Structural Disorder ◽  
Multilayer Films ◽  
Film Plane ◽  
X Ray Diffraction ◽  
X Ray ◽  
Bilayer Films ◽  
Out Of Plane ◽  
Reflectivity Data ◽  
Sharp Interfaces ◽  
Good Agreement

ABSTRACTThe structures of equal-thickness Co/Re multilayer films and several Co/Re bilayer films have been investigated by X-ray diffraction at low and high angles. Analysis of low-angle reflectivity data from bilayer films indicates that interfacial intermixing is limited to three monolayers and that the two interfacial configurations are different. The high-angle X-ray diffraction data show that multilayer films have coherent interfaces and a highly textured structure with hep [002] orientations normal to the film plane for periods 21 Å ≤ Λ ≤220 Å. Detailed structures have been determined by fitting the X-ray spectra to calculated ones using a trapezoidal model. The results indicate that samples with 42 Å≤ Λ ≤220 Å have relatively sharp interfaces, in good agreement with the bilayer results. In addition, an out-of-plane expansion of the Co (002) layer is observed in samples with large Λ and results from structural disorder leading to a reduced atomic density. For Λ <21 Å the interfaces arise from the rougher surfaces of the deposited layers.

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