For finding the atomic structures of new molecules and materials, x-ray diffraction remains the reigning technique of choice. But it’s hampered by a major limitation: Its simplest and most powerful form requires a perfectly crystalline specimen tens of microns on a side—a size that’s beyond crystal growers’ reach for many substances. Because electrons scatter orders of magnitude more strongly than x rays do, electron diffraction has the potential to solve the structures of submicron crystals. But the strong scattering has also been electron diffraction’s downfall: Electrons typically change direction many times on their way through a crystal, and their diffraction patterns are much more difficult to analyze.

For more than 20 years, researchers have been working toward antidotes to that challenge. In precession electron diffraction and electron diffraction tomography, two experimental methods often used together, the electron beam is tilted away from (rather than aligned with) the crystal zone axes; the net effect is the reduced influence of multiple scattering and crystal imperfections. And with a third technique, dynamical diffraction theory, researchers seek to accurately model the remaining multiple scattering to reliably transform the diffraction patterns into a precise atomic structure.

Now Lukáš Palatinus (Czech Academy of Sciences in Prague), Philippe Boullay (CRISMAT Laboratory, CNRS, Caen, France), and their colleagues have combined all three of those methods to derive structural solutions that explicitly locate hydrogen atoms. Previously, hydrogen’s low scattering power and large vibrational amplitudes have combined to produce signals so weak that they were indistinguishable from noise. Crystallographers would have to guess at the H-atom positions once they’d solved for the positions of all the heavier atoms.

Shown here is the Prague and Caen researchers’ structure of paracetamol, also known as acetaminophen. Gray, red, and blue spheres represent carbon, oxygen, and nitrogen atoms, respectively. Yellow blotches represent large local peaks in the electrostatic potential that mark the positions of H atoms; gray blotches are smaller potential peaks that represent noise. The researchers also used their methods, with equal success, on a form of cobalt aluminophosphate whose H atoms introduce internal disorder and whose structure was previously unknown. (L. Palatinus et al., Science 355, 166, 2017.)