Impurity-driven cone formation during laser sputtering of graphite.

Area of Science:

• Materials Science
• Surface Science
• Laser-Material Interactions

Background:

• Highly oriented pyrolytic graphite (HOPG) is an anisotropic material with unique properties.
• Laser sputtering is a process used for material removal and surface modification.
• Understanding material ejection mechanisms and surface evolution under laser irradiation is crucial for various applications.

Purpose of the Study:

• To investigate the sputtering of HOPG using 248-nanometer laser radiation.
• To characterize the translational energies of ejected neutral carbon species.
• To analyze the resulting surface morphology changes on HOPG.

Main Methods:

• Irradiation of HOPG with 248-nanometer laser pulses.
• Analysis of ejected neutral carbon atoms and small clusters.
• Characterization of surface morphology using microscopy techniques.

Main Results:

• Ejection of neutral carbon atoms and clusters with unexpectedly high translational energies.
• Development of a distinct surface morphology characterized by regular cones and domes.
• Identification of trace metal impurities as initiators of cone formation via heat shunting.

Conclusions:

• Laser sputtering of HOPG deviates from simple thermal vaporization models due to high kinetic energies of ejected species.
• Surface morphology evolution, including cone formation, is significantly influenced by trace impurities acting as thermal pathways.
• The study provides insights into laser-induced material modification and surface structuring of anisotropic materials.