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

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.