Tailored SERS Substrate—Ag-WS₂ Nanoflakes Grown by PLD for Highly Sensitive Chemical Sensing Applications

Two-dimensional transition materials dichalcogenides (TMDCs) have a distinct advantage as a surface-enhanced Raman scattering (SERS) substrate because of their exceptional optical features, which facilitate efficient charge transfer with probe molecules and improve chemical enhancement. In this work, vertically oriented WS₂ flakes are synthesized on a Silicon (Si) substrate using the pulsed laser deposition (PLD) technique. WS₂ flakes are then used as SERS substrate for detecting low concentrations (up to 10^-9 M) of Rhodamine B (RhB) and Methyl orange (MO) organic dyes with promising enhancement factors of nearly ~ 10⁷ using 532 nm excitation laser. Using a thermal evaporation process, Ag nanoparticles (NPs) were decorated to further improve the plasmonic activity of vertical WS₂ flakes. WS₂-Ag nanocomposite substrate demonstrates superior detection capabilities when compared to pristine WS₂ flakes, achieving impressive sensitivity at ultralow concentrations of 10^-16 M for RhB and MO dyes and an enhancement factor of the order of 10⁸. The 633 nm laser was utilized to examine the SERS performance of WS₂-Ag substrate for Methylene blue (MB) dye. The MB dye was effectively detected down to an ultra-low concentration of 10^-13 M. In addition to Ag NPs involvement, a charge transfer mechanism between WS₂ and RhB dye molecules is proposed to explain the nanocomposite SERS substrate's excellent detection capabilities and huge enhancement in SERS signal.