For finding the atomic structures of new molecules and materials, x-ray crystallography remains the reigning technique of choice. But it’s hampered by a major limitation: Its simplest and most powerful form requires a crystalline specimen tens of microns on a side—a size that’s beyond crystal growers’ reach for many substances. The size requirement results from two factors: the relatively weak scattering of x rays off atoms in the crystal and the impracticality of focusing x rays onto a submicron spot.
Electrons, because of their charge, scatter orders of magnitude more strongly than x rays do, and they can be focused much more tightly. Electron diffraction, therefore, has the potential to solve the structures of submicron crystals, which are much easier to grow than larger ones. But the strong scattering has also been electron diffraction’s drawback: Electrons typically change direction many times on their way through even a thin crystal, and...
