Molecular Functionalization Tunes Twist Angles of MoS2 Moiré Superlattices for Surface-Enhanced Raman Scattering

In the quest for surface-enhanced Raman spectroscopy (SERS) substrates without noble metals, transition-metal dichalcogenides (TMDs) have emerged as an important class of alternatives. In this regard, molybdenum disulfide (MoS2)-based SERS substrates have been extensively studied; however, their moiré superlattices (with controlled twist angles) could be potent candidates for significant signal enhancement. Here, we employed a molecular functionalization method using 4-aminothiophenol (4-ATP) as a linker to tune the twist angles of MoS2 moiré superlattices. Transmission electron microscopy (TEM) and Raman spectroscopy experiments confirmed the formation of moiré patterns in 4-ATP functionalized MoS2 (4ATP-MoS2), with reduced twist angles in contrast to pristine MoS2 superlattices. Furthermore, we used 4ATP-MoS2 moiré superlattices as SERS substrates to probe molecules, such as rhodamine 6G, rhodamine B, methylene blue, and crystal violet. We observed significant enhancement of Raman signal intensity (on the order of 105) for all the molecules. Interestingly, pristine MoS2 did not show any significant enhancements of the SERS signals. We attribute the enhancement to the moiré interface-induced charge transfer from MoS2 to the probe molecules through 4-ATP, thereby increasing the Raman signals. This strategy could open possibilities to design moiré superlattices for improved SERS substrates and light-matter interactions.