Structural investigation of nanoparticle superlattices by advanced X-ray scattering methods

Colloidal crystals are ordered arrays of colloidal particles forming a superlattice similar to that in conventional crystals. In recent decades, the research on colloidal crystals has blossomed due to their fascinating structure-related properties such as diffraction of light at optical wavelengths, high porosity, etc. Moreover, colloidal crystals are often viewed as a model system for conventional crystals since their larger dimensions allow easier tracing of changes in structure. Mesocrystals are a special subclass of colloidal crystals in which the crystalline nanoparticles constituting the crystal are mutually oriented. Such highly ordered nanocrystal superlattices can display functional collective properties distinct from those of conventional colloidal сrystals and individual nanoparticles. These collective properties are conditioned by the interparticle interactions which are highly dependent on the structural features of the mesocrystals. Even though colloidal crystals and mesocrystals have already found many practical applications, the structure-property relationships are still poorly understood due to the lack of suitable methods of structural investigations.This cumulative Thesis is based on six publications and is devoted to the development of X-ray methods for the structural study of colloidal crystals and mesocrystals.In the first three publications, the structure of colloidal crystals and mesocrystals is revealed by analysis of the measured two-dimensional (2D) scattering patterns. The first publication addresses the structural evolution of a thermoresponsive colloidal crystal consisting of gold–poly(N-isopropylacrylamide) core–shell nanoparticles during cooling and heating. The Bragg peak analysis of the data obtained in Ultra-Small-Angle X-ray Scattering (USAXS) experimental geometry provided a unique insight into the processes of crystallization and melting of such colloidal crystals. The second and third publications deal with mesocrystals consisting of inorganic lead sulfide or lead halide perovskite semiconductive nanoparticles stabilized by organic copper tetraaminophtalocyanine (Cu4APc) or oleic acid (OA) ligands. The experimental geometry allowed the simultaneous registration of both Small-Angle X-ray Scattering (SAXS) from the superlattice structure and Wide-Angle X-ray Scattering (WAXS) from the atomic lattices of the constituting nanoparticles. Analysis of the Bragg peaks registered at both small and wide angles at different spatial points of the sample allowed spatially-resolved structural mapping of the mesocrystals. The extracted superlattice unit cell parameters were combined with the angular orientation of the nanoparticles inside the superlattice to obtain the complete structure of the mesocrystal on both length scales. The revealed structures were then correlated with the measured functional properties of the mesocrystals such as conductivity and photoluminescence.In the other three publications, the structural information is extracted by application of Angular X-ray Cross-Correlation Analysis (AXCCA) to the measured intensity distributions in three-dimensional (3D) reciprocal space. The fourth publication contains the details of adapting this method for application to 3D intensity distributions instead of common 2D scattering patterns. In this work, AXCCA was shown prospective for qualitative structure determination in close-packed colloidal crystals using an exemplary sample consisting of spherical silica particles. In the fifth and sixth publications, AXCCA was successfully applied to the measured 3D scattered intensity distributions to reveal the structure of mesocrystals composed of gold and magnetite nanocubes.The proposed approaches to structural studies of colloidal crystals and mesocrystals can be further extended to other materials. The obtained results on the structure of colloidal crystals and mesocrystals and their correlations with the functional properties are highly novel and are of great interest to the materials science community

In situ characterization of crystallization and melting of soft, thermoresponsive microgels by small-angle X-ray scattering

Depending on the volume fraction and interparticle interactions, colloidal suspensions can form different phases, rangingfrom fluids, crystals, and glasses to gels. For soft microgels that are made from thermoresponsive polymers, the volumefraction can be tuned by temperature, making them excellent systems to experimentally study phase transitions in densecolloidal suspensions. However, investigations of phase transitions at high particle concentration and across the volumephase transition temperature in particular, are challenging due to the deformability and possibility for interpenetrationbetween microgels. Here, we investigate the dense phases of composite core-shell microgels that have a small gold coreand a thermoresponsive microgel shell. Employing Ultra Small Angle X-ray Scattering, we make use of the strong scatteringsignal from the gold cores with respect to the almost negligible signal from the shells. By changing the temperature we studythe freezing and melting transitions of the system in-situ. Using Bragg peak analysis and the Williamson-Hall method, wecharacterize the phase transitions in detail. We show that the system crystallizes into an rhcp structure with differentdegrees of in-plane and out-of-plane stacking disorder that increase upon particle swelling. We further find that the meltingprocess is distinctly different, where the system separates into two different crystal phases with different meltingtemperatures and interparticle interactions

Mapping the 3D position of battery cathode particles in Bragg Coherent Diffractive Imaging

In Bragg coherent diffractive imaging, the precise location of the measured crystals in the interior of the sample is usually missing. Obtaining this information would help the study of the spatially dependent behavior of particles in the bulk of inhomogeneous samples, such as extra-thick battery cathodes. This work presents an approach to determine the 3D position of particles by precisely aligning them at the instrument axis of rotation. In the test experiment reported here, with a 60 µm-thick LiNi0.5Mn1.5O4 battery cathode, the particles were located with a precision of 20 µm in the out-of-plane direction, and the in-plane coordinates were determined with a precision of 1 µm

Microwave Receiving System Based on Cryogenic Sensors for the Optical Big Telescope Alt-Azimuth.

This article presents the results of evaluating the possibility of conducting radio astronomy studies in the windows of atmospheric transparency ~100, ~230, and ~350 GHz using the optical Big Telescope Alt-Azimuthal (BTA) of the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS). A list of some promising astronomical tasks is proposed. The astroclimat conditions at the BTA site and possible optical, cryogenic, and mechanical interfaces for mounting a superconducting radio receiver at the focus of the optical telescope are considered. As a receiving system, arrays of detectors cooled to ~0.3 K based on the superconductor-insulator-normal metal-insulator-superconductor (SINIS) structure are proposed. The implementation of the project will make it possible to use the BTA site of the SAO RAS not only to solve some astronomical problems (it is possible to consider the implementation of a single observatory, the VLBI (very-long-baseline interferometry) mode in the Suffa, EHT (Event Horizon Telescope), and Millimetron projects), but it will also be used to test various cryogenic detectors in a real observatory