Laser phase

A brand new phase of carbon has been created by blasting graphite with a femtosecond laser

Credit: © 2009 APS

Researchers at Osaka University and KEK in Tsukuba have created a new form of solid carbon by exposing graphite to a femtosecond laser¹. The new structure is intermediate between graphite and diamond, and may have some unique electronic properties that can be used in carbon-based devices.

The most common type of bonds between carbon atoms are sp² bonds (as found in the flat hexagonal networks in graphite) and sp³ bonds (as found in diamond). Usually graphite can only transform into diamond at extremely high pressures, but theory predicts that similar transformations might be induced by electronic excitations.

Katsumi Tanimura and co-workers focused femtosecond laser-pulses on graphite samples, and found that the laser created bright protrusions about five nanometres in diameter. They examined these protrusions with scanning tunnelling microscopy, and found that neighbouring pairs of carbon atoms had moved positions to form sp³ bonds — but in a different structural form to diamond.

The sp³ bonds introduce three-dimensional peaks and troughs to the individual graphite layers, and might increase the interactions between adjacent layers. Moreover, the new structure is stable at room temperature. This study opens up the possibility of finding more new phases of carbon through simple optical methods.