Data reduction practice in X-ray reflectometry

Salah, F.; Harzallah, B.; Lee, A. van der

doi:10.1107/s0021889807030403

Cited by 23 publications

(18 citation statements)

References 15 publications

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“…The calculated reflectivity which is compared with the measured reflectivity, after data reduction (see Salah et al, 2007), is then given by its squared modulus, r = jRj 2 . Whereas the algorithm gives the exact reflectivity for a stratified system, it is very cumbersome to apply in leastsquares algorithms because of its high non-linearity.…”

Section: Classical Gradient Methodsmentioning

confidence: 99%

“…For the first sample, no Gaussian broadening was applied for instrumental resolution effects; in the second case, a resolution of 0.001 Å À1 was applied. although in a well defined experiment the noise can be kept constant and certainly lower than 25% by choosing variable step-counting times (Salah et al, 2007). The robustness of the algorithms was tested by varying either one of the parameters, while keeping the other parameters fixed at their model values, or by freeing all parameters at once.…”

Section: Program Usedmentioning

confidence: 99%

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A comparison of modern data analysis methods for X-ray and neutron specular reflectivity data

Lee¹,

Salah²,

Harzallah³

2007

J Appl Cryst

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Data analysis methods for specular X-ray or neutron reflectivity are compared. The methods that have been developed over the years can be classified into different types. The so-called classical methods are based on Parrat's or Abelè s' formalism and rely on minimization using more or less evolved Levenberg-Marquardt or simplex routines. A second class uses the same formalism, but optimization is carried out using simulated annealing or genetic algorithms. A third class uses alternative expressions for the reflectivity, such as the Born approximation or distorted Born approximation. This makes it easier to invert the specular data directly, coupled or not with classical least-squares or iterative methods using over-relaxation or charge-flipping techniques. A fourth class uses mathematical methods founded in scattering theory to determine the phase of the scattered waves, but has to be coupled in certain cases with (magnetic) reference layers. The strengths and weaknesses of a number of these methods are evaluated using simulated and experimental data. It is shown that genetic algorithms are by far superior to traditional and advanced least-squares methods, but that they fail when the layers are less well defined. In the latter case, the methods from the third or fourth class are the better choice, because they permit at least a first estimate of the density profile to be obtained that can be refined using the classical methods of the first class. It is also shown that different analysis programs may calculate different reflectivities for a similar chemical system. One reason for this is that the representation of the layers is either described by chemical composition or by scattering length or electronic densities, between which the conversion of the absorptive part is not straightforward. A second important reason is that routines that describe the convolution with the instrumental resolution function are not identical. research papers J. Appl. Cryst. (2007). 40, 820-833 A. van der Lee et al. Data analysis of specular reflectivity data 821 research papers J. Appl. Cryst. (2007). 40, 820-833 A. van der Lee et al. Data analysis of specular reflectivity data 823

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Section: Classical Gradient Methodsmentioning

confidence: 99%

Section: Program Usedmentioning

confidence: 99%

A comparison of modern data analysis methods for X-ray and neutron specular reflectivity data

Lee¹,

Salah²,

Harzallah³

2007

J Appl Cryst

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“…[16,18] The necessary corrections to be applied to the observed reflectivity data have been described elsewhere. [19] A diagram of the experimental set-up is shown in Figure 2. The measurement cell, where the samples were hold, was manufactured in stainless steel with Mylar windows.…”

Section: X-ray Reflectometry Measurementsmentioning

confidence: 99%

X‐Ray Reflectometry Characterization of Plasma Polymer Films Synthesized from Triallylamine: Density and Swelling in Water

Schieda

Salah

Roualdès

et al. 2013

Plasma Processes & Polymers

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Commercial membranes suitable for solid alkaline membrane fuel cell (SAMFC) have not proved their competitiveness yet, due to poor ionic conductivity and water and fuel retention. Plasma polymers are however promising candidates to meet the SAMFC requirements. In this work, X‐ray reflectometry has been used to determine the thickness, density and water swelling of plasma polymerized films prepared from triallylamine, leading to a bilayer model for the studied thin films. Both film density and water swelling show a bimodal evolution as a function of the average plasma discharge power, which is directly related to the precursor fragmentation mechanism in the plasma phase and can be correlated with the film chemical composition.

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“…The receiving slit in front of the monochromator was set at 0.1 mm. Data were collected using a variable counting time, variable step size strategy to optimize the total data collection time and the counting statistics (Salah et al, 2007). Data were collected up to 6-7 in 2.…”

Section: A11 National Institute For Materials Science Japanmentioning

confidence: 99%

Reproducibility in X-ray reflectometry: results from the first world-wide round-robin experiment

Colombi

Agnihotri²,

Асадчиков

et al. 2008

J Appl Crystallogr

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X-ray reflectometry (XRR) is a well established technique to evaluate quantitatively electron density, thickness and roughness of thin layers. In this paper, results of the first world-wide XRR round-robin experiment, involving 20 laboratories, are presented and discussed. The round-robin experiment was performed within the framework of the VAMAS Project 'X-ray reflectivity measurements for evaluation of thin films and multilayers', the aim of which is to produce a 'good practice' manual for XRR. The reproducibility of measurements obtained using different equipment has been investigated. The influence of the fitting of the experimental data was shown to be non-negligible compared with the experimental factors. The dynamic intensity range proves to be an important parameter for obtaining a good quality measurement. A simpler test sample which does not develop a surface oxide layer over time is now the subject of a follow-up study.

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Data reduction practice in X-ray reflectometry

Cited by 23 publications

References 15 publications

A comparison of modern data analysis methods for X-ray and neutron specular reflectivity data

A comparison of modern data analysis methods for X-ray and neutron specular reflectivity data

X‐Ray Reflectometry Characterization of Plasma Polymer Films Synthesized from Triallylamine: Density and Swelling in Water

Reproducibility in X-ray reflectometry: results from the first world-wide round-robin experiment

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