Surface patterning nanoparticle-based arrays

In this study, focused ion beam lithography is used to pattern different size and shape island arrays on silicon wafers. Cavity arrays of inverse shapes are then made on silicone mold surfaces by polymerization. After that, Al2O3 nanoparticle-based island arrays are created by a surface feature transfer and freeze casting process using an Al2O3 colloidal suspension. The effects of silicone mold surface wettability and freezing rate on the Al2O3 nanoparticle pattern quality are investigated. The results show that coating the silicone mold surface with a 10 nm thick Au–Pt layer makes the Al2O3 nanoparticle suspension more wetting on the mold surface and also likely reduces the dry Al2O3 nanoparticle adhesion to the mold surface. Freezing rate should be lower than 1 °C/min to avoid cracks or loose Al2O3 nanoparticle packing in the freeze cast features. When these factors are properly controlled, the reported patterning process allows reproduction of micron-size feature arrays from Al2O3 nanoparticle suspensions. The studied approach should be applicable to most nanoparticle-based materials and open numerous opportunities for direct-device fabrication.