Nanogap-Rich TiO₂ Film for 2000-Fold Field Enhancement with High Reproducibility

Titanium dioxide (TiO₂) is a crucial semiconductor for photocatalysts, solar cells, hydrogen evolution reactions, and antivirus agents. The properties and performances of these applications can improve significantly if the integrated TiO₂ acts as a light harvester through a large field enhancement. This study investigates the electromagnetic field enhancement of a nanogap-rich TiO₂ film with a large area, prepared by a facile dry process at room temperature. Herein, the loading pressure is applied to the TiO₂ particles for closely packing them in the film. The field enhancement, as a function of the loading pressure, is explored from the fluorescence intensity enhancement of a dye molecule. An average enhancement factor >2000 is achieved, which is a remarkable record for semiconductors. Furthermore, the reproducibility is significant; the relative standard deviation value is small (∼4%). Calculations were performed using the finite-difference-time-domain method. A nanogap of 5 nm yields the highest EF for triangular-prism TiO₂ particles.