Sapphire nanostructures for electronic displays.
You'd think these would be problematic, but this paper is saying it's dirt resistant due to extreme hydrophobicity, and it's even scratch, fog & glare resistant. The full patterning process is explained:
"The nanostructures were patterned using interference lithography, and then transferred to a sapphire substrate using reactive ion etching. Sapphire has a low etching rate due to its chemical stability, and thus a thick polysilicon layer with a thickness of 1000 nm was deposited on the sapphire substrates for use as an etching mask. Subsequently, the samples were spin coated with a 100 nm-thick antireflection coating (Brewer Science, ARC i-con-7) and 200 nm-thick photoresist (Sumitomo, PFi-88A2). The photoresist was exposed using a Lloyd's mirror interference lithography (Kimmon HeCd laser, 325 nm wavelength) to pattern a 2D pillar array with a period of 330 nm. The photoresist pattern was transferred into the underlying ARC, polysilicon, and sapphire substrates using inductively coupled plasma reactive ion etching (ICP, Oxford 100) using O2, HBr, and BCl3/HBr gases, respectively. Notably, a low-RF power was used for the etching of the polysilicon layer with HBr RIE, which significantly increased the silicon to photoresist etch selectivity."