Ordered Au₃Cu Nanocrystals Induced Phase Transformation in 2D-MoS₂ as SERS Substrate for Enhancing Molecular Detection

Abstract

Surface-enhanced Raman scattering (SERS) is one of the potent methods that provides remarkable sensitivity, selectivity, and adaptability for molecular analysis at an ultralow concentration level. Here, we report the synthesis of plasmonic ordered gold−copper alloy (Au 3 Cu) nanocrystals (NCs) with size ∼10 nm, which when dispersed over 2D-MoS 2 resulted in light-induced phase transition from 2H−MoS 2 (semiconducting) to 1T−MoS 2 (metallic). The as-synthesized Au 3 Cu NCs showed a broad UV absorption and broad photoluminescence peak, along with a prolonged plasmonic decay. In Au 3 Cu NC-dispersed MoS 2 , a Schottky junction was formed, and upon light irradiation, the plasmonic hot electrons transferred from Au 3 Cu to MoS 2 , resulting in 2H to 1T phase transformation, thereby effectively strengthening the SERS signals. In this work, we demonstrate that the Au 3 Cu drop-casted MoS 2 (Au 3 Cu/MoS 2 ) substrates can be effectively used for the low-level detection of methylene blue (MB) and dopamine. These ordered Au 3 Cu NCs have homogeneous interparticle nanogaps that offer a stronger enhancement of electromagnetic field (EM) in turn, intensifying the generation of plasmons than the commonly used elemental gold or silver. We believe that the as-prepared Au 3 Cu-ordered NCs and their dispersion over MoS 2 substrates can contribute to the development of Au 3 Cu/MoS 2 systems with improved properties and plasmonic capacity, potentially opening up a wide range of opportunities for the creation of efficient SERS substrates for detecting even minute analyte concentrations.