Predicting pentagonal graphene Available to Purchase

Symmetry precludes the use of regular pentagons to tile a surface. However, as the accompanying figure shows, you can tile with irregular pentagons in a pattern known as Cairo tiling, named after the paving on several streets in Egypt’s capital. According to a new theoretical study by Qian Wang of Peking University and her collaborators, the same pattern can be realized on the atomic scale: in graphene-like sheets of carbon. Carbon structures that feature pentagons have already been synthesized. The archetypal fullerene, C₆₀, comprises 12 pentagons amid 20 hexagons; the smallest, C₂₀, comprises 12 pentagons. Despite those antecedents, the idea that carbon could be coaxed into forming pentagonal sheets arose not from fullerenes but from a new crystalline phase that was predicted three years ago. Known as T12, the phase has two repeating layers, one of which consists of a corrugated arrangement of Cairo-tiled pentagons. Working...