Diffraction patterns degeneration

One of the basic features of high-energy ED is the short wavelength of electrons used 0.05 A (accelerating voltage lOOkV). Therefore Ewald s sphere practically degenerates into a plane, and the electron diffraction pattern (ED) is the planar cross-section of the reciprocal lattice (Fig.2.). 

Crystals of proteins, nucleic acids, viruses, and macromolecular complexes must be handled with considerable care because they are extremely fragile and contain a high proportion of solvent, principally water. Bernal and Crowfoot demonstrated in 1934 that diffraction patterns from protein crystals quickly degenerate upon dehydration in air. Thus it is essential... 

The structure of the ( 5 x. /5)/ 26.6°—Na phase as determined by LEED and DFT calculations [62] is shown in Fig. 13. The structure turns out to be very similar to that of the corresponding Al(lOO)—( 5 x, /5)/ 26.6°—Yb phase, as determined by LEED and photoelectron diffraction [63]. As can be seen from the figure, Na atoms are adsorbed in substitutional sites formed by displacing 1/5 ML A1 atoms from the first A1 layer. It is interesting to note that the structure has only p4, four-fold rotational symmetry, whereas the LEED pattern and intensities exhibit p4mm symmetry. Thus the structure lacks the mirror-plane symmetry of the substrate, and therefore two degenerate domains related by... 

---