Exploring Novel Forms of Carbon

Carbon in its many forms has proven to have a wide range of properties that has made it critical in a wide variety of scientific and technological applications. The element’s great versatility stems from its ability to form single, double, and triple bonds, allowing for a wide array of bonding motifs, all with distinct and, often, very useful properties. With carbon being a material of such fundamental interest, it is strange then that, at present, very little is known about the properties of its liquid state. Extreme pressures (~10 MPa) and temperatures (~5000 K) are required to produce the liquid and these conditions are near to impossible to achieve at equilibrium in a laboratory. As such, it is impossible to isolate liquid carbon and most of its stated properties are speculative.

In an effort to resolve some of the many controversies regarding the liquid, we have set out to make direct experimental measurements of the liquid’s properties.[1] To surmount the need for high temperature and pressure, we produce the liquid through a non-equilibrium process called non-thermal melting [2,3]. In this process, an intense, ultrashort laser pulse is used to promote a significant portion (10-20%) of the electron density into the conduction band. This large degree of excitation weakens the carbon-carbon bonds to the point that the bonds break even at room temperature, resulting in a fluid material that has properties analogous to those of the liquid. The produced liquid remains at the initial material density for a time on the order of picoseconds due to a process known as inertial confinement before ablating away. The non-thermally melted carbon can therefore be probed with any ultrafast technique, yielding information on the liquid’s properties and structure.