Probing ultrafast laser-induced structural transformation in diamond

Ultrafast laser irradiation triggers structural transformations in diamond with broad potential across many fields. Understanding how laser energy modifies the diamond lattice is essential for achieving the intended properties. However, the coupled thermal and mechanical responses make it hard to clarify the transformation pathways. Herein, pump-probe imaging is used to capture surface reflectivity, while a molecular dynamics-coupled two-temperature model (MD-TTM) follows atomistic transformation, revealing thermomechanical behavior and phase transition mechanisms. At fluences below 2.28 J/cm2, the sp3 lattice damage is mainly attributed to Coulomb explosion and remains confined to only a few atomic layers. At elevated fluences, the interaction includes both Coulomb explosion and phase explosion, which not only ablate surface material but also promote notable transformation from sp3 to sp2 bonding. The surface removal initiates shock waves that propagate inward, disrupting the typical compression-to-tension evolution of the stress wave. This leads to residual stress accumulation, relaxation, and renewed buildup with increasing fluence. When the laser fluence increases from 5.05 J/cm2 to above 9.18 J/cm2, the dynamic stress rises from roughly 30 GPa to beyond 100 GPa, resulting in stacking faults and extensive lattice damage within the diamond. Because the material is removed through single-atom ejection instead of cluster flow, the surface roughness remains below 2 nm, along with a low specific contact resistivity of 3×10−6 Ω cm2 and a sheet resistance of 280 Ω. The results outline a processing window that allows efficient surface removal without bulk lattice damage and demonstrate a fast, controllable single-pulse laser strategy for high-quality diamond surface engineering in microelectronic and optoelectronic applications.