Hydrophilic Character of Single-Layer MoS₂ Grown on Ag(111)

High Resolution Image Download MS PowerPoint Slide The study of MoS 2 /metal interfaces is crucial for engineering efficient semiconductor–metal contacts in 2D MoS 2 -based devices. Here we investigate a MoS 2 /Ag heterostructure fabricated by growing a single MoS 2 layer on Ag(111) by pulsed laser deposition under ultrahigh vacuum (UHV) conditions. The surface structure is observed in situ by scanning tunneling microscopy, revealing the hexagonal moiré pattern characteristic of the clean MoS 2 /Ag(111) interface. Ex situ Raman spectroscopy reveals an anomalous behavior of vibrational modes, induced by the strong MoS 2 –Ag interaction. After few-hours exposure to ambient conditions the Raman response significantly changes and the formation of molybdenum oxysulfides is revealed by X-ray photoelectron spectroscopy. These effects are due to the interplay with water vapor and can be reversed by a moderate UHV annealing. A polymeric (PMMA) capping is demonstrated to hinder water-induced modifications, preserving the original interface quality for months.