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Register a new userA Novel Experimental Approach for Nanostructure Analysis: Simultaneous Small Angle X-ray and Neutron Scattering (SAXS/SANS)
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Exploiting small angle X-ray and neutron scattering (SAXS/SANS) on the same sample volume at the same time provides complementary nanoscale structural information at two different contrast situations. Compared with an independent experimental approach, the truly combined SAXS/SANS experimental approach ensures the exactness of the probed samples particularly for in-situ studies. Here, we introduce an advanced portable SAXS system that is dimensionally suitable for installation at D22 zone of ILL. The SAXS apparatus is based on a RIGAKU copper/molybdenum switchable microfocus rotating anode X-ray generator and a DECTRIS detector with a changeable sample-to-detector distance of up to 1.6 m in a vacuum chamber. A science case has been presented to demonstrate the uniqueness of the newly established method at ILL. Temporal structural rearrangements of both, organic stabilizing agents and organically capped gold colloidal particles during gold nanoparticle growth are simultaneously probed, enabling immediate correlated structural information. The newly established nano-analytical method at ILL will open the way for real time investigations of a wide range of innovative nanomaterials and will enable comprehensive in-situ studies on biological systems. A potential development of a fully-automated SAXS/SANS system with a common control environment and additional sample environments, permitting a continual and efficient operation of the system at the hands of ILL users, has also been introduced.
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For obtaining reliable nanostructural details of large amounts of sample --- and if it is applicable --- Small-Angle Scattering (SAS) is a prime technique to use. It promises to obtain bulk-scale, statistically sound information on the morphological details of the nanostructure, and has thus led to many a researcher investing their time in it over the last eight decades of development. Due to pressure both from scientists requesting more details on increasingly complex nanostructures, as well as the ever improving instrumentation leaving less margin for ambiguity, small-angle scattering methodologies have been evolving at a high pace over the last few decades. As the quality of any results can only be as good as the data that goes into these methodologies, the improvements in data collection and all imaginable data correction steps are reviewed here. This work is intended to provide a comprehensive overview of all data corrections, to aid the small-angle scatterer to decide which are relevant for their measurement and how these corrections are performed. Clear mathematical descriptions of the corrections are provided where feasible. Furthermore, as no quality data exists without a decent estimate of its precision, the error estimation and propagation through all these steps is provided alongside the corrections. With these data corrections, the collected small-angle scattering pattern can be made of the highest standard allowing for authoritative nanostructural characterisation through its analysis. A brief background of small-angle scattering, the instrumentation developments over the years, and pitfalls that may be encountered upon data interpretations are provided as well.
Building the European Spallation Source (ESS), the most powerful neutron source in the world, requires significant technological advances at most fronts of instrument component design. Detectors are not an exception. The existing implementations at current neutron scattering facilities are at their performance limits and sometimes barely cover the scientific needs. At full operation the ESS will yield unprecedented neutron brilliance. This means that one of the most challenging aspects for the new detector designs is the increased rate capability and in particular the peak instantaneous rate capability, i.e.,the number of neutrons hitting the detector per channel, pixel or cm$^2$ at the peak of the neutron pulse. This paper focuses on estimating the incident and detection rates that are anticipated for the Small Angle Neutron Scattering (SANS) instruments planned for ESS. Various approaches are applied and the results thereof are presented.
A vacuum-compatible photon-counting hybrid pixel detector has been installed in the ultra-high vacuum (UHV) reflectometer of the four-crystal monochromator (FCM) beamline of the Physikalisch-Technische Bundesanstalt (PTB) at the electron storage ring BESSY II in Berlin, Germany. The setup is based on the PILATUS3 100K module. The detector can be used in the entire photon energy range accessible at the beamline from 1.75 to 10 keV. Complementing the already installed vacuum-compatible PILATUS 1M detector used for small-angle scattering (SAXS) and grazing incidence SAXS (GISAXS), it is possible to access larger scattering angles. The water-cooled module is located on the goniometer arm and can be positioned from -90{deg} to 90{deg} with respect to the incoming beam at a distance of about 200 mm from the sample. To perform absolute scattering experiments the linearity, homogeneity and the angular dependence of the quantum efficiency, including their relative uncertainties, have been investigated. In addition, first results of the performance in wide-angle X-ray scattering (WAXS), X-ray diffraction (XRD) and X-ray reflectometry (XRR) are presented.
We have developed an experimental system to simultaneously observe surface structure, morphology, composition, chemical state, and chemical activity for samples in gas phase environments. This is accomplished by simultaneously measuring X-ray photoelectron spectroscopy (XPS) and grazing incidence X-ray scattering (GIXS) in gas pressures as high as the multi-Torr regime, while also recording mass spectrometry. Scattering patterns reflect near-surface sample structures from the nano- to the meso-scale. The grazing incidence geometry provides tunable depth sensitivity while scattered X-rays are detected across a broad range of angles using a newly designed pivoting-UHV-manipulator for detector positioning. At the same time, XPS and mass spectrometry can be measured, all from the same sample spot and in ambient conditions. To demonstrate the capabilities of this system, we measured the chemical state, composition, and structure of Ag-behenate on a Si(001) wafer in vacuum and in O$_2$ atmosphere at various temperatures. These simultaneous structural, chemical, and gas phase product probes enable detailed insights into the interplay between structure and chemical state for samples in gas phase environments. The compact size of our pivoting-UHV-manipulator makes it possible to retrofit this technique into existing spectroscopic instruments installed at synchrotron beamlines. Because many synchrotron facilities are planning or undergoing upgrades to diffraction limited storage rings with transversely coherent beams, a newly emerging set of coherent X-ray scattering experiments can greatly benefit from the concepts we present here.
Physically, disordered ensembles of non-homopolymeric polypeptides are expected to be heterogeneous; i.e., they should differ from those homogeneous ensembles of homopolymers that harbor an essentially unique relationship between average values of end-to-end distance $R_{rm EE}$ and radius of gyration $R_{rm g}$. It was posited recently, however, that small-angle X-ray scattering (SAXS) data on conformational dimensions of disordered proteins can be rationalized almost exclusively by homopolymer ensembles. Assessing this perspective, chain-model simulations are used to evaluate the discriminatory power of SAXS-determined molecular form factors (MFFs) with regard to homogeneous versus heterogeneous ensembles. The general approach adopted here is not bound by any assumption about ensemble encodability, in that the postulated heterogeneous ensembles we evaluated are not restricted to those entailed by simple interaction schemes. Our analysis of MFFs for certain heterogeneous ensembles with more narrowly distributed $R_{rm EE}$ and $R_{rm g}$ indicates that while they deviates from MFFs of homogeneous ensembles, the differences can be rather small. Remarkably, some heterogeneous ensembles with asphericity and $R_{rm EE}$ drastically different from those of homogeneous ensembles can nonetheless exhibit practically identical MFFs, demonstrating that SAXS MFFs do not afford unique characterizations of basic properties of conformational ensembles in general. In other words, the ensemble to MFF mapping is practically many-to-one and likely non-smooth. Heteropolymeric variations of the $R_{rm EE}$--$R_{rm g}$ relationship were further showcased using an analytical perturbation theory developed here for flexible heteropolymers. Ramifications of our findings for interpretation of experimental data are discussed.
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