Progress of in situ synchrotron X-ray diffraction studies on the mechanical behavior of materials at small scales

In recent years, the mechanical behavior of low-dimensional materials has been attracting lots of attention triggered both by the ongoing miniaturization and the extraordinary properties demonstrated for nanostructures. It is now well established that mechanical properties of small objects differ fundamentally from their bulk counterpart and in particular that "smaller is stronger" but many questions on the deformation mechanisms remain open. Most of the knowledge obtained on small- scale mechanics is based on ex-situ and in-situ characterizations using electron microscopy. However, these techniques suffer from the fact that imaging or scattering information is either limited to the surface or from a 2D projection of a thin foil of material. Within the last two decades tremendous progress was achieved at 3rd generation synchrotrons making it possible to focus hard X-ray beams down to the 100-nm scale. Modern synchrotron X-ray diffraction methods may thus provide structural information with good spatial resolution and fully 3D. In this review, we discuss the progress achieved on in-situ micro- and nano-mechanical tests coupled with different synchrotron X-ray diffraction techniques to monitor the elastic and plastic deformation, highlighting the advantages of these approaches, which offer at the same time versatile sample environments and extreme precision in displacement fields.