Nanosecond laser-induced oriented periodic structures on AlN ceramic

This work presents results on nanosecond laser-induced surface structuring of AlN ceramic. The process under investigation is performed using the fundamental wavelength of Nd:YAG laser system. It is shown that the change of the ambient air pressure from atmospheric one to 10^-4 Torr, leads to modification of the surface morphology – from ripples structure with a periodicity of about the incident irradiation wavelength, to an oriented periodic microstructure with a characteristic period in the range 10–15 µm. In all cases when the periodic structures are formed, a clear orientation perpendicular to the incident irradiation polarization is observed. The properties of the oriented periodic microstructures (OPMSs) formed at the lowest pressure condition are studied in more details, as the influence of the processing conditions on their characteristics is presented. It is found that the formation of OPMS requires a minimal laser pulse number and application of laser fluence above certain threshold. The surface of the fabricated structures is conductive, as the performed analyses indicate that the effect is related to presence aluminium in the processed areas. Possible mechanisms of formation of these structures are discussed. Ablation experiments using irradiation at 532 and 266 nm are also reported and discussed. The presented results may have significant impact when laser processing of AlN ceramics is considered, and for the design of structures with potential applications in microelectronics, tribology, and aluminium-based UV plasmonics.