New Approach for Fast Residual Strain Estimation Through Rational 2D Diffraction Pattern Processing

AbstractA new approach to quantitative XRD by Partial Least Squares (PLS) used region(s) or the entirety of the diffraction pattern of calibration standards (also called a training set) in the model. The basic concept of this approach states that the information in many observed variables, expressed as matrix I = (i1, i2 … , ik,) is concentrated onto a few underlying latent variables, called factors, by the process of data compression. In XRD, the data points of the diffraction pattern are compressed to few factors T, computed according to their ability to explain the variation in the diffraction pattern or matrix I. The procedure incorporates into the model that part of I that is correlated to C concentrations. Data compression preserves the redundancy between variables due to collinearity and stabilizies the predictions against noise in I. The resulting calibration model allows for detection of outliers. Another important effect of data reduction is the ability to analyze muticomponent systems even when lines of the components are overlapped, Examples of quantitative analysis by PLS are demonstrated in the analysis of a commercial product.

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Microscope diffraction pattern processing

10.1117/12.192037 ◽

1994 ◽

Author(s):

Dariusz Litwin

Keyword(s):

Diffraction Pattern ◽

Pattern Processing

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Shift-field refinement of macromolecular atomic models

Acta Crystallographica Section D Structural Biology ◽

10.1107/s2059798320013170 ◽

2020 ◽

Vol 76 (12) ◽

pp. 1192-1200

Author(s):

K. Cowtan ◽

S. Metcalfe ◽

P. Bond

Keyword(s):

Diffraction Pattern ◽

Crystallographic Structure ◽

Model Parameters ◽

Molecular Replacement ◽

Macromolecular Crystallography ◽

Initial Model ◽

New Approach ◽

Structure Solution ◽

Uncertainty Parameters ◽

Key Parameter

The aim of crystallographic structure solution is typically to determine an atomic model which accurately accounts for an observed diffraction pattern. A key step in this process is the refinement of the parameters of an initial model, which is most often determined by molecular replacement using another structure which is broadly similar to the structure of interest. In macromolecular crystallography, the resolution of the data is typically insufficient to determine the positional and uncertainty parameters for each individual atom, and so stereochemical information is used to supplement the observational data. Here, a new approach to refinement is evaluated in which a `shift field' is determined which describes changes to model parameters affecting whole regions of the model rather than individual atoms only, with the size of the affected region being a key parameter of the calculation which can be changed in accordance with the resolution of the data. It is demonstrated that this approach can improve the radius of convergence of the refinement calculation while also dramatically reducing the calculation time.

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Some further considerations in powder diffraction pattern indexing with the dichotomy method

Powder Diffraction ◽

10.1017/s0885715614000906 ◽

2014 ◽

Vol 29 (S2) ◽

pp. S7-S12 ◽

Cited By ~ 26

Author(s):

Daniel Louër ◽

Ali Boultif

Keyword(s):

Computer Program ◽

Diffraction Pattern ◽

Powder Diffraction ◽

Input Data ◽

Zero Point ◽

New Approach ◽

Detailed Review

Some improvements have been introduced in the current computer program for powder diffraction pattern indexing using the dichotomy algorithm. The resulting version, DICVOL14, includes optimizations and extension of scanning limits for triclinic cases, a detailed review of the input data from the indexing solutions, cell centering tests and a new approach for zero-point offset evaluation. The performance of the new version is illustrated with many examples, such as triclinic cases with long axes and dominant zones. Some important parameters in pattern indexing based on the dichotomy algorithm are commented upon, e.g. the precision of data and spurious lines.

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A New Approach to Grow Strain-Free GaAs on Si

MRS Proceedings ◽

10.1557/proc-202-609 ◽

1990 ◽

Vol 202 ◽

Cited By ~ 1

Author(s):

Hyunchul Sohn ◽

Eicke R. Weber ◽

Jay Tu ◽

Shyh Wang

Keyword(s):

Residual Strain ◽

Lattice Mismatch ◽

Gaas Layer ◽

Threading Dislocations ◽

New Approach ◽

Thermally Induced ◽

Si Substrates ◽

Growth Area ◽

The Difference ◽

Substrate Patterning

ABSTRACTThe major problems of the GaAs/Si heteroepitaxy are the high density of threading dislocations and the high residual strain in the GaAs epilayers. The residual strain in the epilayer is attributed to the difference in contraction during cooling down from the growth temperature. It was reported previously that the residual stress in GaAs epilayer could be reduced by reducing the growth area using substrate patterning. In this paper, we report a new approach to grow strain- free GaAs layer on Si substrates. The residual strain in GaAs/Si is tensile in nature, therefore we attempted to compensate this thermally induced strain by compressive lattice mismatched strain. The thermally induced strain in the GaAs layer was successfully compensated by the lattice- mismatch induced strain using In0.032Ga0.968As. By that method, we could grow thin strain- free GaAs layers on Si without patterning. The strain relieving effect was confirmed by photoluminescence experiment.

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High-throughput powder diffraction. I. A new approach to qualitative and quantitative powder diffraction pattern analysis using full pattern profiles

Journal of Applied Crystallography ◽

10.1107/s002188980400038x ◽

2004 ◽

Vol 37 (2) ◽

pp. 231-242 ◽

Cited By ~ 35

Author(s):

Christopher J. Gilmore ◽

Gordon Barr ◽

Jonathan Paisley

Keyword(s):

Diffraction Pattern ◽

Powder Diffraction ◽

High Throughput ◽

Pattern Analysis ◽

Statistical Tests ◽

Integrated Approach ◽

Data Sets ◽

New Approach ◽

Qualitative And Quantitative ◽

Value Decomposition

A new integrated approach to full powder diffraction pattern analysis is described. This new approach incorporates wavelet-based data pre-processing, non-parametric statistical tests for full-pattern matching, and singular value decomposition to extract quantitative phase information from mixtures. Every measured data point is used in both qualitative and quantitative analyses. The success of this new integrated approach is demonstrated through examples using several test data sets. The methods are incorporated within the commercial software programSNAP-1D, and can be extended to high-throughput powder diffraction experiments.

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