In efforts to build ultrathin electronic circuits—for applying to cell phones, human skin, and more—the conductive material of choice is often graphene. (See, for example, Physics Today, September 2022, page 17.) Electrons flow freely through the honeycomb carbon sheets, just as they do through graphene’s bulk parent material, graphite.
But graphene is a semimetal, not a metal. Rather than a continuous partially filled band of plentiful electronic states, graphene has valence and conduction bands that touch at just a few discrete points. It has no bandgap, but the quantum states that contribute to charge transport aren’t as plentiful as they might be.
Although true metals are rare among two-dimensional materials, a notable exception is a class of materials called MXenes (pronounced “Maxines,” like the name), with the general formula M2X, where M is a transition metal and X is carbon or nitrogen. (Thicker structures of the form M3X2 or M4X3 are also possible.) In addition to being electrically conductive, MXenes are valued for their chemical properties, with applications in catalysis, energy storage, and more.
Despite their promise, MXenes have been difficult to make cleanly. But the University of Chicago’s Dmitri Talapin and colleagues are working to change that, with not one but two new MXene synthesis routes that could help streamline basic research and open the door to more practical industrial production.
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