# Simultaneous SAXS/SANS Method at D22 of ILL: Instrument Upgrade
## 1 Introduction  
Small angle scattering (SAS) of X-rays (SAXS) and neutrons (SANS) are non-destructive powerful techniques which have been utilized successfully for investigating nanostructured materials such as metal nanoparticles [1, 2], emulsions [3], micelles [4, 5], electrolytes [6, 7], liquid crystals [8, 9] and organic nanoparticles [10, 11, 12, 13]. The SAS technique provides nanoscale information including shape, size, and size distribution as well as spatial distribution of dispersed materials in solution [14, 15]. In particular, they provide the diameter of gyration and the mass of isotropically distributed shaped nanoscale particles [16], as well as the linear mass density and cross-sectional size of anisotropically shaped particles [14, 17]. Moreover, SAXS and SANS methods are important tools for examining materials for various applications, e.g., solar cells, lithium-ion batteries and sensors [6, 7, 18, 19, 20, 21]. Combining both SAXS and SANS methods to investigate the same sample volume is remarkably advantageous, where two radiations offer two different contrast situations (X-ray and neutron scattering cross section). Using such multiple modalities is very beneficial, especially for cases when a single modality provides incomplete or ambiguous results. For instance, SANS provides the form factor of the shell in a representative hollow-shell-like particle [2]. In contrast, SAXS measurements of the same core-shell sample are sensitiveto the high-electron-density core. The structures of both shell and core can be uniquely obtained from the same sample volume via complementary SAXS and SANS methods. Thus, simultaneous SAXS/SANS measurements will allow the exactness of the probed samples and the potential for using a common analysis model for both SAXS and SANS data, and consequently, a straightforward and unambiguous interpretation of the scattering data. For instance, structural modifications of supramolecular gels upon switching between H\({}_{2}\)O and D\({}_{2}\)O have been reported [22]. The deuteration effect on the structure of some nanoscale structured samples cannot be ignored. Thus, the simultaneous SAXS/SANS method is an essential tool for eliminating any ambiguity regarding sample exactness. A key contribution of the simultaneous SAXS/SANS method is its ability to perform in situ and operando studies on advanced materials that undergo temporal modifications under external stimuli [23], allowing access to their structural rearrangements from the molecular scale to nanoscale assemblies. This means not only the synergy that results when data sets are obtained simultaneously from the same sample volume, but also access to the cross-correlation of phases/components when two different simultaneous contrast situations are probed for multi-phase/component samples. For instance, the cross-correlation between evolved gold nanorods size/shape (SAXS) and the corresponding engaged structure of organic moieties (SANS) during surfactant-assisted seed-mediated synthesis of gold nanorods will reveal new information related to the exact growth mechanisms involved [23]. Moreover, the SAXS/SANS system will enable contrast-dependent successive length-scale characterization of novel nanomaterials, addressing unsolved scientific questions. A few instruments at neutron research reactors are currently utilized for both neutron and X-ray radiation experiment, obtaining complementary results of investigated samples. These dedicated instruments are mainly reflectometry and imaging techniques. A neutron imaging setup at PSI is outfitted with an additional X-ray tube to perform computerized tomography (CT) investigations using X-ray and neutron radiation [24; 25]. Similarly, an instrument (NeXT) at ILL hosts two complementary imaging setups; neutron and X-ray tomography [26; 27]. Neutron reflectometers such as the NREX instrument at MLZ allows combined X-ray and neutron specular reflectivity measurements using both X-ray and neutron beams placed in an orthogonal geometry [28].