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

Abstract

Titanium dioxide (TiO 2 ) 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 TiO 2 acts as a light harvester through a large field enhancement. This study investigates the electromagnetic field enhancement of a nanogap-rich TiO 2 film with a large area, prepared by a facile dry process at room temperature. Herein, the loading pressure is applied to the TiO 2 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 TiO 2 particles.

Large Field Enhancement of Nanocoral Structures on Porous Si Synthesized from Rice Husks

“…Interestingly, the size of ∼200 nm is in good agreement with that predicted by Mie scattering for a spherical Si particle producing the highest efficiency, as shown in Figure m. − According to Mie scattering theory, the value of Q sca is proportional to the square of the electric field of the scattered light, corresponding to the magnitude of EF Figure e.…”

“…An objective lens (SMLPLN, 100×, Olympus) with a long working distance was used to obtain the spectrum for the CV solution under a cover glass. The optical cell for collection of the spectrum was designed to provide a solution layer between the cover glass and the Si powder. − The EF values associated with the fluorescence intensities were obtained by acquiring four spectra, wherein the enhanced spectrum of the CV was divided by the spectrum of the CV, both of which had the background signals subtracted, as described in our reports previously. − Fluorescence mapping measurements were conducted by collecting CV spectra with the same instrument and by scanning the sample in the cell on an x–y translation stage, as described in our report previously. ,, The grid size of the mapping data was due to the scan step of the stage, which was set to 500 nm, and the data collection time of the spectrum was 1 s. Using the mapping data, EFs were obtained and layered over the SEM image of the same sample.…”

Incoherent Optical Tweezers on Black Titanium

“…It was recently reported that nanostructured TiO 2 can enhance the E-field intensity of the incident light with a factor of 10 3 −10 4 . 43,44 On the other hand, we never detected any sign of trapping using 370 nm light from a Hg lamp for a flat (mirror-polished) TiO 2 crystal. This indicates that such enhancement effects strongly assist the laser-free optical trapping phenomenon observed here.…”

Fast, Economical, and Reproducible Sensing from a 2D Si Wire Array: Accurate Characterization by Single Wire Spectroscopy

“…The concentration of the dye solution was set to 3.6 × 10 –5 M. The optical cell for spectrum collection was designed to provide a solution layer between the cover glass and the 2D-SiWA substrate. The configuration between the cell and an optical system is similar to previous approaches. − …”

“…The EF values associated with the fluorescence intensities were obtained by acquiring four spectra: (1) the fluorescence spectrum of the dye solution with the 2D-SiWA ( I 1 ); (2) the fluorescence spectrum of the dye solution without the dye ( I 2 ); (3) the background spectrum of (1) with methanol as the solvent ( I 3 ) and with 2D-SiWA included in the solution; (4) the background spectrum of (2) with methanol as the solvent, without the 2D-SiWA ( I 4 ). The EF of fluorescence intensity was then obtained using these four spectra, according to EF = ( I 1 – I 3 )/( I 2 – I 4 ), similar to previous approaches. − …”