Basic idea
Disordered, nano-structured or reduced-dimensional crystals often lack sufficient long-range order to produce sharp diffraction peaks, but still show short range order, i.e. the local atomic structure, resulting broad and less intense peaks. This local structure is described quantitatively by the atomic pair distribution function technique which is also known as total scattering analysis. From the measured X-ray diffractogram the so-called structure function (factor) is determined following initial basic data reduction steps. The radial atomic pair distribution function is then calculated by a Fourier transformation. The pair distribution function describes the probability of finding two atoms separated by a certain distance in the material under investigation. Software is then used to find the structural model that best fits the determined PDF function.
Compatibility of BL 12.2.2
Using short wavelengths provides a high Qmax and thus better r-space resolution for quantitative structural analysis to be attempted. The highest achievable x-ray energy at beamline 12.2.2 is about 35 keV, corresponding a Q range limited to ~12 Å-1. Our previous research show reliable data sets Fourier transformed with reasonably minimized truncation errors and allowing interpretable results in real space. Our previous published studies motivate us go further and work on structure calculations in disordered materials even if the data is restricted in Q-range.
This figure shows details of the data reduction process to obtain the structure factors S(Q). (a) The sample (black solid line) and background (red solid line) scattering collected from sample and sample cavity (includes ruby chip and pressure transmitting fluid) at ambient conditions. Also shown are the patterns after background and absorption corrections (blue solid line) and normalization (yellow solid line). (b) Compton scattering, f 2(Q) and Krogh−Moe−Norman normalization. (c) The total structure factor of GeSe4 glass. Inset: A photograph of the sample and ruby chip inside diamond anvil cell. See here further details.
Further reading shown below contains a reasonable number of works including beamline 12.2.2 data.
+SCAN: Interactive visualization of high-pressure x-ray scattering analses
+SCAN is an interactive data reduction program for total structure factor analysis of x-ray diffraction data from disordered phases. The software is designed for easy use, automated operation and quick data analysis. The outputs from +SCAN are the total structure factor in momentum space and its Fourier transform, the radial distribution function in real space. The software has been verified by reducing the experimental x-ray diffraction data from various amorphous samples and comparing their radial distribution functions to previously published results in the literature.
