Structural transformation of monocrystalline diamond driven by ultrashort laser pulses

Abstract

We report on morphological and phase transformations in monocrystalline diamond (type—IIa) caused by tightly focused femtosecond laser pulses. Laser-induced periodic surface structure (LIPSS) of high spatial frequency was observed under multiple-pulse surface irradiation. An average spatial periodicity of 140±15nm was independent of the incidence fluence. Compositional analysis performed to evaluate the structural properties of the irradiated region showed existence of graphite and amorphous carbon. The cross-sectional analysis of the area with use of a transmission electron microscopy (TEM) revealed a thin layer of amorphous carbon with a thickness of a few tens of nanometers, capping the monocrystalline diamond. A more detailed inspection of the internal structure within the layer with a high-resolution TEM (HRTEM) highlighted presence of different nano-graphitic structures, immersed in the amorphous carbon and giving in this way diamond-like-carbon (DLC). Formation of two graphite sheets from three diamond planes (111) was revealed as the main transformation process at the interface. Generally, graphite sheets tended to have diverse curved forms. The sub-layer area consisted of defected crystalline diamond with few cracks due to mechanical force exerted at the high laser fluence. © 2016 Elsevier B.V