Photo-Induced Structural Dynamics of Graphite Studied by Ultrafast Electron Crystallography.

The graphite to diamond conversion is believed to involve the rhombohedral phase of graphite as an intermediate state. Using ultrafast electron crystallography, we have observed the formation of transient interlayer \textit{sp}$^{3}$ bonds in graphite beyond a threshold fluence, leading to a non-thermal structural change (Raman, R. K. et al$.$ Phys. Rev. Lett. 101, 077401 (2008)). This transient rebonding towards diamondization is likely driven by a compressive Coulomb stress created by the photoinduced charge separation following the initial E$_{2g}$ phonon excitation that alters the layering symmetry within graphite.