Material‐Dependent Functionalization of CVD‐Grown TMDC Monolayers Probed by Vibrational Nanospectroscopy

Understanding the molecular‐level mechanisms governing covalent functionalization of two‐dimensional semiconductors remains a major challenge. Here, we investigate the chemical vapor deposition (CVD) growth of monolayer MoSe 2 , WSe 2 , and MoSe 2 ‐WSe 2 in‐plane heterostructures, which were subsequently transferred onto conductive Au(111) substrates using a contamination‐ and defect‐free protocol. Tip‐enhanced Raman spectroscopy (TERS) and photo‐induced force microscopy (PiFM) are high‐resolution scanning probe techniques, enabling colocalized topographical and vibrational spectroscopic mapping of surface structures and bound‐molecules, providing sub‐diffraction of light spatial resolutions. Using TERS, we provide unique Raman nanospectroscopy analyses and imaging of lateral and vertical‐lateral MoSe 2 ‐WSe 2 nanodomains and alloyed heterojunctions. Applying PiFM, we directly visualize electrodeposited aryl diazonium salts, providing key direct nanoscale chemical evidence of 4‐carboxyphenyl (4‐CP) and 4‐nitrophenyl (4‐NP) covalent functionalization on transition metal dichalcogenides (TMDCs) and their respective heterostructures in protic and organic solvents, revealing material‐dependent reactivity. Atomistic molecular dynamics simulations reveal that 4‐nitrobenzenediazonium cations (4‐NBD + ) interact more strongly with MoSe 2 than WSe 2 , exhibiting persistent interfacial hydration and reduced mobility, which localizes precursors at the interface. This sustained interfacial availability rationalizes the experimentally observed higher reduction probability and grafting efficiency on MoSe 2 . Together, these findings provide a robust molecular‐level framework for solvent‐ and material‐dependent covalent functionalization of two‐dimensional TMDC monolayer materials.