One downside of electron microscopy is that the electron beam can damage the materials being imaged by breaking bonds and changing molecular structures. But Jamie Warner and his colleagues at the University of Oxford, UK, used this to their advantage, and obtained unprecedented pictures of crystals forming at the atomic level.

They directed an 80-kilovolt electron beam through a thin film of 'peapods' — carbon nanotubes containing spheres of carbon atoms called buckyballs. Each buckyball contained two atoms of praseodymium. Prolonged exposure to the beam caused the buckyballs to coalesce, forming an inner nanotube. The praseodymium atoms were released into this inner nanotube, allowing them to form praseodymium carbide crystals.

The images reveal that the crystals formed as a result of atoms coalescing into clusters, which, in turn, clumped together, rather than by atoms being added one at a time to a single growing crystal.

ACS Nano doi:10.1021/nn1031802 (2011)