Watching nanomaterials with X-ray eyes: Probing different length scales by combining scattering with spectroscopy

Everybody dreams to have X-ray eyes and discover the most invisible secrets of the world around us. X-rays can probe matter (depth resolved) down to atomic resolution, if relying on diffraction-based techniques. An X-ray diffraction pattern may contain information over many length scales (atomic structure, microstructure, mesostructure). This peculiarity justifies the well-recognized impact of several X-ray diffraction-based techniques to diverse fields of research. On the other hand, X-ray spectroscopies (both in absorption and in emission) provide insights on the electronic structure and, exploiting element selectivity and local environment, can complement or even replace scattering techniques for diluted systems and amorphous materials. Herein, we provide a theoretical foundation which spans from very basic concepts, through well-known techniques, with applications to nanomaterials research. An increasing level of material complexity is explored: size and shape analysis of nanoparticles dispersed in solution or single nanostructures localized onto surfaces; local morphology/strain analysis of nanostructured surfaces; average defects analysis of stacking faulted nanocrystals; regular 2D and 3D lattices of self-assembled nanocrystals; clusters of nanocrystals without any nanoscale lattice order, standing alone as isolated objects or embedded in tenths-of-µm-thick polymers (here coherent and focused X-rays are mandatory to explore the spatial inhomogeneity and lattice (in)coherence of the materials).