Optical Hot Spot Generation by the Plasmonic Coupling of Au Nanoparticles in the Nanospaces of Mesoporous Titanium(IV) Oxide

Atsunobu Akita; Musashi Fujishima; Hiroaki Tada

doi:10.1021/acs.langmuir.0c03184

Optical Hot Spot Generation by the Plasmonic Coupling of Au Nanoparticles in the Nanospaces of Mesoporous Titanium(IV) Oxide

Langmuir. 2021 Feb 9;37(5):1838-1842. doi: 10.1021/acs.langmuir.0c03184. Epub 2021 Jan 29.

Authors

Atsunobu Akita¹, Musashi Fujishima², Hiroaki Tada^{1

2}

Affiliations

¹ Graduate School of Science and Engineering, Kindai University, 3-4-1, Kowakae, Higashi-Osaka, Osaka 577-8502, Japan.
² Department of Applied Chemistry, Faculty of Science and Engineering, Kindai University, 3-4-1, Kowakae, Higashi-Osaka, Osaka 577-8502, Japan.

PMID: 33513306
DOI: 10.1021/acs.langmuir.0c03184

Abstract

An in situ reduction technique consisting of chemisorption of 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS) and subsequent reaction with HAuCl₄ has been developed for depositing Au nanoparticles (NPs) uniformly in the depth direction of a mesoporous TiO₂ nanocrystalline film (Au/TMCTS/mp-TiO₂). The TMCTS monolayer is further converted into silicon oxide by heating in the air (Au/SiO_x/mp-TiO₂). In the absorption spectra of Au/SiO_x/mp-TiO₂ prepared at varying HAuCl₄ concentrations (C), the localized surface plasmon resonance (LSPR) band of Au NPs significantly broadens C ≈ 1.22 mM at 546 nm to be split into two peaks around 500 and 700 nm at C ≥ 2.43 mM, whereas such a phenomenon is not observed for the usual Au NP-loaded TiO₂ particles. Three-dimensional-finite difference time domain simulations showed that the unique optical property of Au/SiO_x/mp-TiO₂ stems from the effective LSPR coupling of very close Au NPs and partial fusions in the nanospaces of mp-TiO₂. Further, the optical hot spots in Au/TMCTS/mp-TiO₂ as well as Au/SiO_x/mp-TiO₂ generate an intense local electric field giving increase to a great enhancement of the absorption in the infrared spectrum of the TMCTS monolayer on mp-TiO₂.