Laser-induced structural modifications of glassy carbon surfaces

Abstract

Structural modifications induced by pulsed laser irradiations in the surface layers of glassy carbon have been monitored by reflection high energy electron diffraction, Raman spectroscopy, and electron energy loss spectroscopy. The glassy carbon samples were irradiated by 30 superimposed laser pulses (λ́=6.943 nm). The energy density (100–500 mJ/cm2 per pulse) delivered to the material and the repetition rate of the laser (0.05 Hz) have been chosen so that the temperature increase of the irradiated surface layers was below the melting point of the glassy carbon. The combined use of the analysis techniques indicated that the beginning of the solid state processes, leading to microstructural modifications of the surface layers, occurs at energy density of 300 mJ/cm2. An increase of the average crystalline size of graphitic clusters occurs upon radiation performed at fluences of 300 and 400 mJ/cm2, whereas at higher energy density the material undergoes complete amorphization. The analysis of chemical state and microstructure of the irradiated samples clearly demonstrates that graphitization or, conversely amorphization of glassy carbon surface layers can be achieved by a proper choice of the laser irradiation conditions.