Small- and Wide-Angle X-Ray Scattering (SAXS/WAXS) with Temperature-Controlled Stages Makes Phase Identification Faster than Ever
Han Wu1 and Duncan Stacey2 *
duncanstacey@linkam.co.uk
Abstract: X-ray diffraction (XRD) is a fingerprint technique for the analysis of atomic and molecular structures of crystalline materials, from polymers and plastics, through to structural composites and biomaterials. These all have crystallographic phases in the nanostructure, which greatly influence the macro properties of the material—from insulin and hemoglobin to semiconductors and solar cells. Here, we look at how XRD analysis using a small- and wide- angle X-ray scattering (SAXS/WAXS) system under full vacuum brings the possibility of crystallographic sample characterization, with temperature and environmental control, direct to the laboratory, and how this improves the workflow for phase identification.
Keywords: X-ray diffraction, small- and wide- angle X-ray scattering, crystal, temperature control, in-house
Introduction X-ray diffraction (XRD) encompasses various experi-
mental techniques that work by irradiating the sample with incident X-rays in order to measure the elastic scattering angle and intensity of the X-rays leaving the sample material. Te diffraction pattern and intensity can correlate directly with specific crystalline components in the sample, giving a picture of the crystal phase, as well as details on defects and deformi- ties within the material that deviate from the perfect crystal structure. Characterization using temperature-controlled XRD is a useful analytical tool for solids, liquids, and powder samples across many research applications, including solar cell research, drug discovery, and life sciences (Figure 1). Tere are various forms of X-ray scattering techniques,
including small- and wide-angle X-ray scattering (SAXS and WAXS), which differ by measuring the scattered X-rays at small (2θ=0-5°) or wide angles (2θ >5°), respectively. While SAXS and WAXS work widely with powder or liquid samples, grazing incidence (GI) SAXS and WAXS is oſten applied for thin film samples that can be irradiated at a shallow incident angle close to the critical angle (0.1° to 1°). Synchrotron facilities, such as Diamond in the UK, offer
high-powered X-ray beamlines capable of performing XRD analysis on a wide range of samples. Tese national centers oſten host multiple beamlines with specific modifications for SAXS or WAXS, and traditionally this has been the only route for researchers to access this type of analysis. More recently, in-house XRD and SAXS/WAXS devices, which scale down the beamline to enable the equipment to fit within a standard laboratory, have become available. Tese bring quicker and easier access to crystallographic characterization, with more control over sample conditions for environmental analysis, such as temperature, humidity, and gas flow. One such in-house SAXS/WAXS system is housed at the Centre for Nature-Inspired Engineering (CNIE), Department of
30 doi:10.1017/S1551929521001358
Chemical Engineering, at University College London. Established in 2014, the CNIE research facility supports multi-disciplinary research across the University, and access is available for academic and industrial collaborators and users. Access to the facility can be obtained by contacting Dr. Han Wu via their website (
https://www.ucl.ac.uk/nature-inspired-engineering/facilities). Users of the facility can access a range of instruments worth
over £6 million to characterize their samples, including: liquid TEM, a nano 3D printer, a dynamic light scattering (DLS) system, a differential scanning calorimeter (DSC), and thermal gas thermogravimetric analysis (TGA) and TGA mass spectrometry (TGA/MS) instruments. Among its state-of-the-art instruments, the facility has a unique in-house small/wide-angle X-ray scattering (SAXS/WAXS) instrument, the Ganesha 300XL. Used independently, and in tandem with the Ganesha 300XL and other instruments, are several temperature-controlled stages, including the Linkam capillary X-ray stage and the HFSX350-CAP stage, which has a capillary tube through the heating block to enable observation of the temperature-dependent behavior of food and pharmaceuticals, batteries, fuel cells, catalysis, and architecture materials; and the optical Linkam DSC450, which provides enthalpy data (Figure 2). Te temperature-controlled DSC450 enables liquid nitrogen temperatures without the need for large liquid nitrogen dewars when performing temperature-controlled experiments. Additional temperature-controlled stages include the HFSX350-CAP, which allows sample preparation inside a small capillary, and thus carefully controlled environmental condition at high vacuum inside an XRD chamber.
In-House SAXS/WAXS for Rapid Phase Identification X-ray scattering is a well-established technique for the
characterization of polymers, pharmaceuticals, nanoparticles, and biological materials [1–3]. WAXS provides structural information at the atomic scale down to 0.1nm, similar to traditional XRD. SAXS provides
information on complex
molecules and materials such as polymers, colloids, and porous materials, up to 500nm in size. Typically, SAXS/WAXS is used for small-angle scattering studies. However, with the CNIE equipment’s whole-vacuum setup, wide-angle X-ray scattering can offer rapid data collection with very precise temperature control and easy sampling. Tere is also an important energy- saving benefit because cryo temperatures can be obtained with just 1 liter of liquid nitrogen. Te whole-vacuum SAXS/WAXS system that was developed by SAXSLAB can be used to evaluate multi-scale structures, such as atomic structure (0.2nm to 1nm) and molecular structure (1nm to 100nm). It can also be used
www.microscopy-today.com • 2021 November *
1Centre for Nature Inspired Engineering, University College London, UK 2Linkam Scientific Instruments, Surrey, UK
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