Mie scattering induced a dominant electromagnetic enhancement on the Bi2WO6@Bi2O3 SERS substrate via submicron-morphology design

Abstract

Semiconductors are making significant strides in the field of surface enhanced Raman scattering (SERS), but they face challenges due to the difficulty of matching noble metal substrates, as their limited chemical enhancement stems from a low charge transfer (CT) contribution. Mie scattering achieved by designing a laser wavelength comparable morphology provides a supplementary electromagnetic enhancement source for semiconductor substrates. Herein, a Bi₂WO₆@Bi₂O₃ SERS substrate composed of Bi₂O₃ nanopillars wrapped by Bi₂WO₆ nanoflowers was synthesized using a hydrothermal method and exhibited an ultra-low detection limit of 10⁻¹⁰ M and a superb enhancement factor of 1.88 × 10⁹ when detecting methylene blue (MeB) molecules under a 532 nm laser. The abundant oxygen vacancy defect energy levels in the composite substrate facilitate CT resonance enhancement, spanning from a laser range from 532 nm to 633 nm laser. Though the 633 nm laser is conducive to the strongest CT resonance, the submicron-morphology has considerably enhanced the surrounding electromagnetic field under the 532 nm laser by Mie scattering resonance, contributing to at least 10³ Raman signal enhancement and coordinating with the moderate CT resonance and MeB molecular resonance to jointly improve the SERS enhancement. In short, this work demonstrated the considerable potential of Mie scattering by the appearance design to improve the sensitivity of SERS substrates.