Researchers create a one-dimensional crystal

Graphene, a sheet of carbon one atom thick, has properties that are distinct from other forms of carbon—even graphite, which is just a bulk collection of graphene sheets. That's prompted researchers to look into other forms of what are called two-dimensional materials (at an atom thick, the third dimension isn't counted). And now, they've started experimenting with one-dimensional materials, which are essentially a line of single atoms.

Unfortunately, single atoms aren't especially cooperative about getting in line. Even stable crystals, like those formed by a salt, stay together in part because there are multiple interaction partners for each atom that stabilize the structure. Putting atoms in a line gets rid of most of these interactions, leaving the remaining ones unstable.

But researchers have figured out a way around this problem: they've managed to pack a line of atoms inside a carbon nanotube. Having chosen cesium iodide for their work, they simply had to pick a diameter that was larger than the atoms (over 3.4 Angstroms) but smaller than you'd need to put two atoms side-by-side (less than 8 Angstroms). They chose double-walled carbon nanotubes and loaded them with CsI simply by vaporizing the chemical under pressure.

Inside the tube, the atoms actually ended up closer together than they are in a crystal (the bond length was about 10 to 15 percent shorter). In addition, the cesium atoms looked unusually large. This turned out to be because the iodine atoms tend to interact more strongly with the carbon nanotubes, pinning them in place. By contrast, the cesium vibrates inside, making it appear larger than it actually is.

In general, the paper is mostly focused on showing that it is possible to create what's essentially a single row of atoms. But in reality, the material isn't entirely one-dimensional. Both atoms interact with the carbon nanotubes, which means that the material has some properties that are a result of its container, rather than simply being the product of the atoms themselves. But the authors have already moved on to load carbon nanotubes with a variety of other salts (they mention CsCl, CsF, NaI, and AuBr₃), so it's clear that they intend to thoroughly study how these odd materials behave.

Nature Materials, 2014. DOI: 10.1038/NMAT4069  (About DOIs).