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Although there has been significant interest in the novel material properties of bio-inspired nanostructures, engineering them to become mechanically durable remains a significant challenge. This work demonstrates the fabrication of sapphire nanostructures with anti-glare, anti-fogging, anti-dust and scratch-resistant properties. The fabricated nanostructures demonstrated a period of 330 nm and an aspect ratio of 2.1, the highest reported for sapphire thus far. The nanostructured sapphire sample exhibited broadband and omnidirectional antireflection properties, with an enhanced transmission of up to 95.8% at a wavelength of 1360 nm. The sapphire nanostructures also exhibited enhanced wetting performance and could mitigate fogging from water condensation or repel water droplets. Furthermore, owing to their sharp features, the fabricated structures could prevent particulate adhesion and maintain a 98.7% dust-free surface area solely using gravity. Furthermore, nanoindentation and scratch tests indicated that the sapphire nanostructures have an indentation modulus and hardness of 182 GPa and 3.7 GPa, respectively, which are similar to those of bulk glass and scratch-resistant metals such as tungsten. These sapphire nanostructures can be fabricated using high-throughput nanomanufacturing techniques and can find applications in scratch-resistant optics for photonics, electronic displays, and protective windows. 

Abstract Sapphire is an attractive material that stands to benefit from surface functionalization effects stemming from micro/nanostructures. Here we investigate the use of ultrafast lasers for fabricating sapphire nanostructures by exploring the relationship between irradiation parameters, morphology change, and selective etching. In this approach a femtosecond laser pulse is focused on the substrate to change the crystalline morphology to amorphous or polycrystalline, which is characterized by examining different vibrational modes using Raman spectroscopy. The irradiated regions are removed using a subsequent hydrofluoric acid etch. Laser confocal measurements quantify the degree of selective etching. The results indicate a threshold laser pulse intensity required for selective etching. This process was used to fabricate hierarchical sapphire nanostructures over large areas with enhanced hydrophobicity, with an apparent contact angle of 140 degrees, and a high roll-off angle, characteristic of the rose petal effect. Additionally, the structures have high broadband diffuse transmittance of up to 81.8% with low loss, with applications in optical diffusers. Our findings provide new insights into the interplay between the light-matter interactions, where Raman shifts associated with different vibrational modes can predict selective etching. These results advance sapphire nanostructure fabrication, with applications in infrared optics, protective windows, and consumer electronics.