Ductile mode material removal and high-pressure phase transformation in silicon during micro-laser assisted machining

Micro-laser assisted machining is a novel micro/nano machining technique developed for ductile mode machining of ceramics and semiconductors. Ductile mode material removal is possible in a nominally brittle material due to the high-pressure phase transformation (HPPT) phenomenon during the machining process. This paper investigates the mechanism of machining by analyzing the HPPTs under different scratch conditions, with and without laser heating. Micro-Raman (μ-Raman) spectroscopy studies of the nano-scratched regions provided evidence for HPPT in single crystal Silicon (Si). Annealing of the high-pressure phases into a recrystallized diamond structure (Si-I) at higher laser powers and its effect on machining characteristics is also discussed. This has been the first time that HPPT is reported in the material removed region where the material's phase transformation and laser heating occur simultaneously and instantaneously (the annealing process occurs instantaneously and is not time dependent in this case).

► We scratched Si with 3 conditions (no laser, 10 W and 45 W) using a novel technique.
► Micro-laser assisted machining preferentially heats only the phase transformed region.
► Optimized laser power (45 W) yielded in the deepest cut for similar applied loads.
► Micro Raman spectroscopy is used to study the high pressure phases.
► High laser powers gets the surface back to Si-I by annealing the high pressure phases.