Fabrication of wafer-scale TiO2 nanobowl arrays via a scooping transfer of polystyrene nanospheres and atomic layer deposition for their application in photonic crystals

Abstract

In this study, wafer-scale triangularly patterned two-dimensional (2D) TiO₂ nanobowl structures were fabricated on 4 in. glass and polyethylene terephthalate (PET) substrates using a combination of two simple processes: (1) the fabrication of self-assembled arrays of polystyrene (PS) nanospheres based on a scooping transfer technique and (2) atomic layer deposition (ALD). To demonstrate the effectiveness of the TiO₂ nanobowl as a photonic crystal layer (PCL), we investigated the optical properties of a 2D TiO₂ nanobowl-assisted Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce) ceramic plate phosphor (CPP)-capped white LED by changing the bowl sizes, the number of bowl layers, and the shell thickness. Using an optimized 2D TiO₂ nanobowl PCL (580 nm lattice constant, one layer, and a shell thickness of 58 nm), the luminous efficacy was improved by a factor of 1.54 compared to that of a conventional CPP-capped white LED. The 2D TiO₂ nanobowl structures fabricated on a large scale and with various substrates may find potential application in optical, electronic, and biological devices.