Tuning the Refractive Index Sensitivity of LSPR Transducers Based on Nanocomposite Thin Films Composed of Noble Metal Nanoparticles Dispersed in TiO2

Diogo Costa; Marco S Rodrigues; Eduardo Alves; Nuno P Barradas; Joel Borges; Filipe Vaz

doi:10.3390/ma16237355

Tuning the Refractive Index Sensitivity of LSPR Transducers Based on Nanocomposite Thin Films Composed of Noble Metal Nanoparticles Dispersed in TiO₂

Materials (Basel). 2023 Nov 26;16(23):7355. doi: 10.3390/ma16237355.

Authors

Diogo Costa¹, Marco S Rodrigues¹, Eduardo Alves², Nuno P Barradas³, Joel Borges^{1

4}, Filipe Vaz^{1

4

5}

Affiliations

¹ Physics Center of Minho and Porto Universities (CF-UM-UP), University of Minho, Campus de Azurém, 4800-058 Guimarães, Portugal.
² Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal.
³ Centro de Ciências e Tecnologias Nucleares, Instituto Superior Técnico, Universidade de Lisboa EN10, 2695-066 Bobadela, Portugal.
⁴ LaPMET-Laboratory of Physics for Materials and Emergent Technologies, University of Minho, 4710-057 Braga, Portugal.
⁵ Material Science Department, Transilvania University of Brasov, 29 Eroilor Blvd., 500036 Brasov, Romania.

Abstract

This work reports on the development of nanoplasmonic thin films consisting of Au, Ag, or Au-Ag nanoparticles dispersed in a TiO₂ matrix and the optimization of the deposition parameters to tune their optical response. The thin films were produced by reactive DC magnetron sputtering of a Ti target with Au and/or Ag pellets placed on the erosion zone. The thicknesses (50 and 100 nm) of the films, the current density (75 and 100 A/m²) applied to the target (titanium), and the number of pellets placed on its surface were the deposition conditions that were used to tailor the optical (LSPR) response. The total noble metal content varied between 13 and 28 at.% for Au/TiO₂ films, between 22 and 30 at.% for Ag/TiO₂ films, and 8 to 29 at% for the Au-Ag/TiO₂ systems with 1:1, 1:1.5, and 1:2 Au:Ag atomic ratios. After thermal annealing at 400 and 600 °C, LSPR bands were found for all films concerning the Au-TiO₂ and Au-Ag/TiO₂, while for Ag/TiO₂, only for thin films with 28 and 30 at.% of Ag concentration. Refractive index sensitivity (RIS) was evaluated for Au and Au-Ag/TiO₂ thin films. It was found that for bimetallic nanoparticles, the sensitivity can increase up to five times when compared to a monometallic nanoplasmonic system. Using Au-Ag/TiO2 thin films can decrease the cost of fabrication of LSPR transducers while improving their sensitivity.

Keywords: localized surface plasmon resonance (LSPR); noble metal nanoparticles; plasmonic sensing; reactive magnetron sputtered; refractive index sensitivity; thin films.

Abstract

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