Wafer-scale high aspect-ratio sapphire periodic nanostructures fabricated by self-modulated femtosecond laser hybrid technology.

Sapphire nanostructures with a high aspect-ratio have broad applications in photoelectronic devices, which are difficult to be fabricated due to the properties of high transparency and hardness, remarkable thermal and chemical stability. Although the phenomenon of laser-induced periodic surface structures (LIPSS) provides an extraordinary idea for surface nanotexturing, it suffers from the limitation of the small depth of the nanostructures. Here, a high-efficiency self-modulated femtosecond laser hybrid technology was proposed to fabricate nanostructures with high aspect-ratios on the sapphire surface, which was combined backside laser modification and subsequent wet etching. Due to the refractive index mismatch, the focal length of the laser could be elongated when focused inside sapphire. Thus, periodic nanostructures with high-quality aspect ratios of more than 55 were prepared on the sapphire surface by using this hybrid fabrication method. As a proof-of-concept, wafer-scale (∼2 inches) periodic nanostripes with a high aspect-ratio were realized on a sapphire surface, which possesses unique diffractive properties compared to typical shallow gratings. The results indicate that the self-modulated femtosecond laser hybrid technology is an efficient and versatile technique for producing high aspect-ratio nanostructures on hard and transparent materials, which would propel the potential applications in optics and surface engineering, sensing, etc.