An efficient SERS substrate for target molecule aggregation and localization Analysis: WS2 nanoparticles in pitted a-plane GaN

In this study, we employed metal–organic chemical vapor deposition (MOCVD) to grow pitted a-plane GaN with triangular pits of approximately several micrometers in size on r–plane sapphire substrates. Subsequently, WO₃ nanoparticles were sulfurized in a furnace, undergoing high–temperature deoxygenation and sulfur bonding to form irregularly shaped WS₂ nanoparticles. These WS₂ nanoparticles were then titrated onto the GaN substrate. Due to the polar nature of the atomic lattice arrangement of GaN along the c-axis, scanning electron microscopy revealed that WS₂ particles were attracted to the pits by the polar electric field caused by the Ga and N faces of the GaN, forming a WS₂/a-plane GaN heterostructure. Using Rhodamine 6G (R6G), a polar biological dye, as the target molecule, Raman spectroscopy results indicated that R6G primarily accumulated in the pits. Further surface–enhanced Raman scattering (SERS) analysis demonstrated that this heterostructure effectively increased carrier transition paths and enhanced charge transfer opportunities when detecting R6G. The enhancement factor in the pits reached up to approximately 10⁷, with an outstanding limit of detection of 10⁻¹⁰ M. This study confirms that the WS₂/pitted a-plane GaN heterostructure, with its micron-sized triangular pits advantageous for locating analytes, holds significant potential for aggregating polar molecules and serving as a SERS substrate. This makes it a promising candidate for high-efficiency biomedical detection technologies, thereby enhancing detection efficiency.