Two-dimensional periodic surface nanotexturing of 6H-SiC by ultrashort laser pulses

Circularly polarized femtosecond laser pulses have successfully promoted the formation of Two-Dimensional Laser Induced Periodic Surface Structures (2D-LIPSS) exhibiting a sub-wavelength periodicity of 150 ± 20 nm on semi-insulating 6H-SiC samples. The main objective of this study was to discern the formation of two-dimensional LIPSS depending on the single pulse energy and the number of pulses released per unit area. The experimental laser system used in this study generates pulses with a duration of 100 fs, a wavelength of 800 nm, and operates at a repetition rate of 1 kHz. Micro-Raman spectroscopy confirms the presence of the characteristic 6H-SiC peaks across all irradiated samples, indicating that the processing technique does not induce significant compositional variations. Nonetheless, the analysis reveals the induction of compressive stress within the lattice structure. Samples treated across the entire surface were characterized by using optical analysis in order to assess the induced variations in absorptance and emittance due to laser irradiation. The treated samples exhibit solar absorptance values of approximately 75 % and a high spectral selectivity up to 2.0 for temperatures higher than 1000 K. This highlights the potential of fs-laser surface textured 6H-SiC plates as viable selective solar absorbers for energy conversion devices operating at elevated temperatures.