Atomic-scale insight into the removal mechanism and microstructure evolution of CVD diamond in picosecond laser processing

Abstract

Chemical vapor deposition (CVD) diamond's excellent mechanical and optical properties make it valuable for microelectronics and optical devices, with ultrashort pulsed lasers offering effective micro/nano-scale processing. However, the interaction mechanisms between these lasers and CVD diamond remain complex, particularly regarding how grain boundaries influence the ablation process. This study develops an enhanced two-temperature model (TTM) coupled with molecular dynamics (MD) that uniquely incorporates dynamic optical property changes and plasma shielding effects. The one-dimensional and two-dimensional TTM-MD simulations reveal that grain boundary volume fraction significantly affects the ablation depth and graphite layer thickness during picosecond laser ablation of CVD diamond. The distribution of grain boundaries substantially alters ablation pit morphology, while reducing the propagation speed of the stress waves, causing uneven stress distribution in polycrystalline diamond. Furthermore, 1/2〈110〉  dislocations primarily distribute along grain boundaries, while 1/6〈112〉 dislocations cyclically form and annihilate during ablation. Transmission electron microscopy characterization confirms the simulation results of grain boundary graphitization, crack formation, and dislocation distribution patterns. This work provides atomic-scale insights into grain boundary effects during ultrashort-pulse laser processing of CVD diamond, establishing a theoretical foundation and practical guidance for ultra-precision micro/nano-machining of diamond.