P21.1 specializes in high-energy x-ray diffraction and scattering experiments in complex sample environments and enables panoramic overview of reciprocal space up to high momentum transfer q. The beamline provides the capabilities for basic diffraction applications to in situ and operando processes or on large samples. For more details, the list below gives a selection of dedicated techniques offered at P21.1.
Single-crystal total and diffuse scattering
P21.1 provides dedicated instrumentation to study strongly correlated electron materials that exhibit properties such as superconductivity or colossal magnetoresistance. The main purpose is to determine lattice distortions caused by static or dynamic symmetry breaking of spin, charge, orbital and lattice degrees of freedom, and to reveal the metastable ground states that emerge upon their competition or frustrated interaction. Through external stimuli like magnetic and electric fields, and uniaxial or hydrostatic pressure, the coupling strength of the different degrees of freedom can be tuned and the balance between different phases can be changed.
In order to fully understand the intricate structure of such complex materials, it may be key to combine information on the local order as well as the average, periodic ordering incl. superlattice structures. P21.1 enables the detection of Bragg reflections and of diffuse scattering over a large part in reciprocal space up to high reflection orders. The large-area and high dynamic range CdTe photon-counting detectors are capable of recording diffuse scattering and Bragg reflections simultaneously. Consequently, large parts of the 2D diffraction pattern are captured upon a single sample rotation and are suitable to determine the average structure as well as the local order, e.g. by applying the 3D-ΔPDF approach. In the optional Eulerian cradle, the single crystal is oriented by a UB matrix for high-resolution measurements utilizing the analyzer crystal and small area/ point detector. Different types of helium cryostats and a 10T horizontal field cryomagnet complement the instrumentation for single crystal studies at P21.1.
Total scattering and powder diffraction
Over the past two decades, the development of nanomaterials has been enhanced significantly by the fast-growing availability and usage of the x-ray total scattering (TS) technique and atomic pair distribution function (PDF) analysis as a unique tool to describe their local atomic order. P21.1 provides the necessary high photon energies to access the high Q range in reciprocal space which, in combination with large and fast area detectors, enable in situ and operando PDF studies with high time resolution (also known as rapid acquisition PDF). Standard sample environments for heating and cooling of capillaries and flat samples are readily available and partly compatible with a helium/ vacuum chamber for suppression of air scattering.
P21.1 is designed as a versatile high-energy diffraction and scattering beamline giving the users the flexibility to use vastly different experimental setups from simple capillary holders up to complex sample manipulation systems. Owing to its high load capacity and large available mounting space, the diffractometer is able to carry large and heavy sample environments such as vacuum or reaction chambers. Varying the sample to detector distance between 300 mm for total scattering and a few meters for classic diffraction allows for setting the desired Q range and resolution. Real-time data processing, e.g. azimuthal integration, and visualization give the users instant feedback to react on unexpected results or developments of their samples.
Combined small-angle scattering and total scattering
For the characterization of nanoparticles, total scattering and PDF analysis of the atomic structure complement small-angle x-ray scattering (SAXS) which provides morphological parameters such as size and shape. While high-energy x-rays ≥60 keV are very favorable for TS and PDF, their compression of reciprocal space limits the maximum observable sizes in SAXS by squeezing the Qmin range into the beamstop. As it is highly desirable to simultaneously follow atomic structure and particle size and shape during in situ reactions such as nanoparticle synthesis, P21.1 provides a combined TS-SAXS setup that offers a compromise between the conflicting optimum conditions for the two techniques. In this way, the data collected for the different scattering regimes give access to structural information on the length scale from angstroms to a few tens of nanometers. The PDF describes the coherent domain size in real space and reaches out to 5-10 nm. When the domains grow bigger, powder diffraction (PXRD) is better suited to quantify the domain size, size distribution and shape by Rietveld analysis of the periodic atomic structure in reciprocal space. Given the high photon energy of 100 keV at P21.1, diffraction patterns suitable both for PDF and limited Rietveld analysis are recorded on a large area detector placed at an intermediate sample to detector distance (~0.8 m) and covering one quadrant of the diffraction cones (direct beam in one corner). This setup allows applying the most suitable analysis method to the same dataset for different stages of the reaction. As nanoparticles rarely crystallize as single-domains, synchronous SAXS measurements are necessary to obtain information on the size of the formed individual particles and potential aggregates. Additionally, nanoparticle superlattice structures, can be investigated both with respect to the atomic order inside the particles as well as their arrangement into periodic structures via linker molecules.
Multimodal approaches
Besides recording the atomic structure, some experiments benefit from obtaining chemical information. An energy-resolving point detector for x-ray fluorescence measurements is part of the beamline equipment. In the frame of the Virtual Laboratory for Instrumental Analysis (VIA), more complementary techniques to the x-ray scattering and diffraction experiments are available. These include e.g. spectroscopic methods (UV-vis-NIR, FTIR, Raman) and mass spectrometry, partly for online measurements at the beamline and partly for offline sample characterization in the lab. More information on the instrumentation pool and how to get access is found on https://photon-science.desy.de/facilities/petra_iii/sample_environment__laboratories/analytical_methods_via/index_eng.html
