Guide to surface x-ray diffraction analysis

Here are some walkthroughs to aid in the analysis of surface x-ray diffraction measurements

Crystal Truncation Rods

Reflectivity

In-plane omega scans
Crystal Truncation Rods Reflectivity In-plane omega scans

Specular 00L rods

GIWAXS

GISAXS
Specular 00L rods GIWAXS GISAXS

Reflectivity ( low angle \(\theta-2\theta scans\))

These are specular measurements taken at low \(\theta\) values near the critical edge of your sample, and can be analysed with the following steps:

  • Reduce the data to a 1D reflecitivty profile, which can be done using the islatu package

  • use a program such as GenX to model the reflectiity profile

Specular 00L rod ( \(\theta-2\theta scans\))

These are specular measurements taken at higher \(\theta\) values, away from the critical edge of your sample. These can be analysed using the following steps:

  • Reduce the data to a 1D profile, which can be done using the islatu package

  • Peak positions and widths can be used for quantitative analysis of your 00L profile

  • Out-of-plane strain can be calculated by analysing HKL positions

  • The 00L profile can be loaded into fitting programs such as ROD for full structure fitting. There are also options for automating ROD

Note

For a full structural fit, the specular 00L profile is usually combined with off-specular crystal truncation rod measurements.

Crystal truncation rod data

These are measurements taken with a fixed incident angel, and along the L direction at a variety of HK positions, which can take both integer and fraction positiosn of H and K. These can be analysed using the following steps:

  • Map the data from raw images into HKL space, which can be done using the fast_rsm package

  • Reduce the 3D HKL volumes data into 1D profiles, which can be done using the binoviewer package (under development)

  • The off-specular CTR profiles can be loaded into fitting programs such as ROD for full structure fitting. There are also options for automating ROD

In-plane omega scans

These are measurements taken at fixed very low L value, and are collected by rocking the sample around it azimuthal axis. These can be analysed using the following steps:

  • Reduce the raw data to individual intensities for each HK position. See extra information on reducing omega scan data

  • The 00L profile can be loaded into fitting programs such as ROD for full structure fitting - Note: these are usually combined with off-specular crystal truncation rod measurements. There are also options for automating ROD

Note

For a full structural fit, the in-plane omega scans are usually combined with off-specular crystal truncation rod measurements

Grazing incidence wide angle x-ray scattering

These are measurements taken with a large detector position close to the sample, and usually require some form of azimuthal integration. These can be processed in the following steps:

  • obtain calibration information so you know the detector distance from your sample

  • azimuthally integrated the data or map the data into 2D co-ordinate system (Q_parallel Vs Q_Perpendicular, exit angles)

both of these steps can be done using the pyFAI python package. For Diamond data sets the fast_rsm package already makes use of the pyFAI module.

Grazing incidence small angle x-ray scattering