Nanosecond pulsed laser-processing of CVD diamond

This work considers the resulting material structural effects of laser-processing chemical vapor deposited (CVD) diamond. The utilized 532 nm wavelength laser had a pulse duration of 40 ns together with a spot diameter of ca. 40 mu m. The effect of cutting fluence on the CVD diamond microstructure was investigated using both Raman and transmission electron microscopy (TEM) analyses. While Raman analysis showed that increasing the laser fluence led to a transition from diamond to graphite, the spread of the beam and consequent interrogation volume leads to limitations in understanding the precise structure over the ablated diamond surface. As such, TEM showed that at a low fluence (4.9 J/cm(2)), the subsurface microstructure is a mix of both graphite and amorphous carbon (aC). At 15 J/cm(2), only the graphite phase was identified. As the fluence increases further, the thickness of the graphite layer decreases until it disappears at a fluence of 50 J/cm(2). In contrast, a crystalline diamond phase began to be identified at 15 J/cm(2) and grows with increasing fluence. Moreover, cracks were visible only until a fluence of 15 J/cm(2), while at higher fluences, no cracks were observed. A simulation model was developed to predict the residual graphitization thickness formed in CVD diamond by a laser beam. Despite some differences in the graphite layer thickness, the results obtained from the model were consistent with the TEM results, supporting the findings of this study. Finally, cracks were only located in the graphite phase at the two lowest laser fluences. This was due to the low fracture toughness of graphite as compared to diamond.