Fabrication of Ag-perovskite substrates for surface-enhanced Raman scattering via all-vacuum deposition

Abstract

The first all-vacuum deposition for fabricating perovskite-based substrates for surface-enhanced Raman scattering (SERS) is reported. While thermal deposition of silver nanoparticles is commonly employed to generate Ag substrates for SERS detection, Raman measurements on blank Ag substrates usually exhibit undesired fluctuations in the spectra. These fluctuations, acting as noise, significantly hinder the detection of low-concentration analytes when using the substrates for SERS. Remarkably, adding a perovskite layer to the substrate (referred to as an Ag-perovskite substrate) dramatically reduces this fluctuation. The fabrication of the Ag-perovskite substrate begins with thermal co-deposition of CsI and PbI₂ at a 1 : 0.9 ratio, resulting in a 20-nm-thick mixture. This mixture is then annealed at 100 °C for 3 min in a nitrogen glovebox to form perovskite. Subsequently, a 7-nm-Ag layer is thermally deposited onto the sample, completing the creation of the Ag-perovskite substrates. We used Ag-perovskite substrates to efficiently detect analytes such as thiabendazole (TBZ), thiram, and rhodamine 6G (R6G). Notably, this substrate exhibited an outstanding limit of detection (LOD) of 10⁻⁹ M for R6G under an excitation wavelength of 532 nm. Furthermore, our investigations extended to practical scenarios, where we successfully demonstrated the substrate's efficacy in detecting TBZ, a pesticide, in apple juice, achieving a LOD of 10⁻⁷ M. Impressively, this LOD surpasses the U.S. Environmental Protection Agency's mandated maximum residue limit of 5 ppm (∼2.5 × 10⁻⁵ M). These results underscore the immense potential of such SERS substrates for real-world applications in pesticide residue detection.