Sapphire substrates with different crystal orientations are widely used in optoelectronic applications. In this work, focused ion beam (FIB) milling of single-crystal sapphire with A-, C-, and M-orientations was performed. The material removal rate (MRR) and surface roughness (Sa) of sapphire with the three crystal orientations after FIB etching were derived. The experimental results show that: The MRR of A-plane sapphire is slightly higher than that of C-plane and M-plane sapphires; the Sa of A-plane sapphire after FIB treatment is the smallest among the three different crystal orientations. These results imply that A-plane sapphire allows easier material removal during FIB milling compared with C-plane and M-plane sapphires. Moreover, the surface quality of A-plane sapphire after FIB milling is better than that of C-plane and M-plane sapphires. The theoretical calculation results show that the removal energy of aluminum ions and oxygen ions per square nanometer on the outermost surface of A-plane sapphire is the smallest. This also implies that material is more easily removed from the surface of A-plane sapphire than the surface of C-plane and M-plane sapphires by FIB milling. In addition, it is also found that higher MRR leads to lower Sa and better surface quality of sapphire for FIB etching.

The nanohole arrays on the silicon substrate can effectively enhance the light absorption in thin film silicon solar cells. In order to optimize the solar energy absorption, polystyrene microspheres with diameters of 1 μm are used to assist picosecond laser with a wavelength of 1064 nm to fabricate nanohole arrays on silicon substrate. The experimental results show that the morphology and size of the silicon nanoholes strongly depend on the laser fluence. At 1.19–1.59 J/cm² laser fluences, well-ordered arrays of nanoholes were fabricated on silicon substrate, with diameters domain from 250 to 549 nm and depths ranging from 60 to 99 nm. However, large amounts of sputtered nanoparticles appeared around the silicon nanoholes. To improve the surface morphology of silicon nanoholes, a nanolayered gold coating is applied on silicon surface to assist laser processing. The results show that, for gold-coated silicon substrate, sputtered nanoparticles around the nanoholes are almost invisible and the cross-sectional profiles of the nanoholes are smoother. Moreover, the ablation rate of the nanoholes on the gold-coated silicon substrate have increased compared to that of the nanoholes on the uncoated one. This simple method allows fast fabrication of well-ordered nanoholes on silicon substrate without sputtered nanoparticles and with smooth inner surface.