Anisotropy antireflection TiO₂ nanoparticle films fabricated with directed cluster beam deposition

Antireflection TiO₂ nanoparticle film was fabricated on silica glass substrate by using directed cluster beam deposition method. Self-shadowing becomes a dominant growth mechanism for nanoparticle deposition at suffi{ligature}ciently large incident angles, which results in extremely porous nanoparticle stacking and yields excellent control over the refractive index profile. Inclined columnar and porous microstructure was confirmed with SEM and AFM. The TiO₂ nanoparticle films show ultra-high transmittance, broadband and omnidirectional characters, which can be attributed to its porous structure and modulated refractive index. We also found that the film displays an angular selective optical transmittance. The highest antireflection enhancement of the light transmission can be obtained for light incidence along the nanoparticle columns.