Formation mechanisms of silicon surface structuring using single-multiple nanosecond laser pulses in ambient air and cold plasma

The formation mechanisms of the surface structures of silicon using single-multiple nanosecond laser pulses at the focus, and below the focus in ambient air and cold plasma was investigated for ablation at 2-5 J cm-2. Ablation in cold plasma, excited by a dielectric-barrier-discharge source in flowing air by applying sinusoidal voltage of 3-5 kV/30 kHz led to regular and consistent low-spatial-frequency and high-spatial-frequency gratingtype structures. For plasma, structures were formed inside the crater and suggest that plasma hindered effective coupling of the laser energy to the surface, which resulted in a controlled ablation. Contrary to the ablation in plasma, for ambient air, due to excessive ablation, overlapped-ripples were formed outside the ablation crater. For the increased laser shots fired below the focus, the surface pattern spatially expands and sustains a far-range order. The localized interrupted and broken features were also observed due to the incubation effect of statically fired laser shots. This study finds that ablation in clod plasma seems a promising new concept to use for shaping and structuring surfaces of industry-accepted materials for electronic and photonic devices, such as solar-cells, detectors, large-area grating, and optical waveguides.