Ultra-short pulsed laser microstructuring of diamond

Precision microfabrication of diamond has many applications in the fields of microelectronics and cutting tools. In this work, an ultra-short pulsed Ti: Sapphire laser was used to perform patterning, hole drilling, and scribing of synthetic and CVD diamonds. Scanning electron microscopy, atomic force microscopy, profilometry, and Raman spectroscopy were employed to characterize the microstructures. A tight-binding molecular dynamics (TBMD) model was used to investigate atomic movements during ablation and predict thresholds for ablation. The ultra-short pulsed laser generated holes and grooves that were nearly perfect with smooth edges, little collateral thermal damage and recast layer. The most exciting observation was the absence of graphite residue that always occurs in the longer-pulsed laser machining. The ablation threshold for ultra-short pulsed laser was two orders of magnitude lower than that of longer-pulsed laser. Finite-difference thermal modeling showed that ultra-short pulses raised the electron temperatures of diamond in excess of 100,000 K due to multiphoton absorption, absence of hydrodynamic motion, and lack of time for energy transfer from electrons to the lattice during the pulse duration. TBMD simulations, carried out on (111) and (100) diamond surfaces, revealed that ultra-short pulses peel carbon atoms layer-by-layer from the surface, leaving a smooth surface after ablation. However, longer pulses cause thermal melting resulting in graphite residue that anchors to the diamond surface following ablation.