ReaxFF reactive molecular dynamics simulation of the oxidation of silicon-doped amorphous carbon film in heat-assisted magnetic recording

Heat-assisted magnetic recording (HAMR) is one of the promising ways to extend the magnetic recording area density to 1 Tb·in⁻² in hard disk drives (HDDs). High temperature induced by laser heating can cause carbon overcoat (COC) oxidation. Reactive molecular dynamics (MD) simulations are performed to investigate the oxidation process of silicon-doped amorphous carbon (a-C:Si) films for HAMR application. The atomic details of the structure evolution and oxidation process are investigated, and, the oxidation mechanism of the a-C:Si film is clarified. The effect of the duration of laser irradiation on the oxidation of the a-C:Si film is investigated. The oxidation occurs during heating and the beginning of cooling process. Both volume expansion during heating process and cluster of carbon atoms during cooling process increase the rate of sp² carbon. Because of the decrease in the amount of unsaturated silicon atoms and low diffusion coefficient of atomic oxygen, the oxidation rate of the a-C:Si film decreases with laser irradiation cycles. The molecular oxygen is the oxidant due to surface defect of a-C:Si film. The atomic strains break the O―O bonds in Si―O―O―Si linkages and rearrange the surface oxide layers, and process the oxidation of the a-C:Si film.