Monocristal (Fr). Einkristall (Ge). Monocristallo (It). Monocrystal (Sp). Монокристалл (Ru).
A single-crystal is a solid material in which the crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no grain boundaries. Single crystals are a requirement for X-ray diffraction experiments.
Typically, crystals have flat faces and sharp edges. Also, many crystals will have one or more directions that can be cleaved cleanly. The sufficient single crystal size for an X-ray diffraction measurement is around (0.01 mm)3, for modern X-ray devices. Single crystals bigger than some (0.3 mm)3 can be reduced in size in order to provide satisfactory size for an XRD measurement.
For crystals on the sub-micro and nanometer scale, standard X-ray devices (including Synchrotron facilities) are not capable of producing enough diffraction on these particles to characterize the molecular structure. On the other hand, Electron Diffraction techniques can do that. Furthermore, a dedicated device, like an electron diffractometer, would be the best option fur such regime of samples.
1 “Single crystal”, accessed on September 21, 2020, https://en.wikipedia.org/wiki/Single_crystal
2 “Symmetry in crystallography”, accessed on September 21, 2020, http://xrayweb.chem.ou.edu/notes/symmetry.html
3 W. Massa, “Crystal structure determination”, 3rd Ed., Books on Demand, Norderstedt 2016, 99-100.