Impurity-driven cone formation during laser sputtering of graphite

Sputtering of highly oriented pyrolytic graphite (HOPG) by 248-nanometer laser radiation was studied. Neutral carbon atoms and small clusters were ejected with significantly higher translational energies than were expected from a simple model of thermal vaporization in the absence of a potential barrier. The HOPG also developed a remarkable surface morphology that consists of regular cones and domes. Cone formation appears to be initiated by trace metal impurities that serve as heat shunts in this highly anisotropic material.