Chinese scientists have developed a method for making thin microfibers of carbon nitride. Carbon fibers are already mixed with plastics to make very strong yet lightweight composites that are used in a wide range of applications, from helicopter blades to fishing rods. Carbon nitride materials could become even more useful, as certain forms are predicted to be harder than diamond. But it has proven extremely difficult to make microscopic fibers of the material. Now, a team of scientists led by Lianfeng Sun of the National Center for Nanoscience and Technology, and Sishen Xie of the Institute of Physics, Chinese Academy of Sciences, Beijing, have cracked the problem.1

First, they used the commonly-available chemical melamine to make graphitic carbon nitride (C3N4.4), where carbon and nitrogen atoms are arranged into flat, hexagonal patterns similar to graphite itself. Heating the material to 680 °C broke up these molecular sheets into a vapour containing fragments of just a few carbon and nitrogen atoms.

Fig. 1: A clump of carbon nitride microfibers.

This vapour then coalesced onto the inner surface of a quartz tube to make fine fibers with an average diameter of 0.8 micrometres. The largest fibers reached almost one millimeter in length (Fig. 1) without needing a catalyst to speed up or direct their growth. Shining a laser onto the fibers makes them glow blue—this photoluminescence is characteristic of molecular structures containing rings of carbon and nitrogen atoms. The scientists also used transmission electron microscopy to study the atomic structure of the microfibers. While most the atoms in the fibers were arranged into flat, graphitic sheets, the team also found small crystalline regions. This atomic arrangement is similar to that of graphite, and exhibits sp2 bonding feature.

The team hopes to adapt their method to make other carbon nitride structures, including even thinner fibers and tiny spheres.