Pulsed laser deposition of single-layer MoS₂ on Au(111): from nanosized crystals to large-area films

Molybdenum disulphide (MoS₂) is a promising material for heterogeneous catalysis and novel two-dimensional (2D) optoelectronic devices. In this work, we synthesized single-layer (SL) MoS₂ structures on Au(111) by pulsed laser deposition (PLD) under ultra-high vacuum (UHV) conditions. By controlling the PLD process, we were able to tune the sample morphology from low-coverage SL nanocrystals to large-area SL films uniformly wetting the whole substrate surface. We investigated the obtained MoS₂ structures at the nanometer and atomic scales by means of in situ scanning tunneling microscopy/spectroscopy (STM/STS) measurements, to study the interaction between SL MoS₂ and Au(111)-which for example influences MoS₂ lattice orientation-the structure of point defects and the formation of in-plane MoS₂/Au heterojunctions. Raman spectroscopy, performed ex situ on large-area SL MoS₂, revealed significant modifications of the in-plane E12g and out-of-plane A_1g vibrational modes, possibly related to strain and doping effects. Charge transfer between SL MoS₂ and Au is also likely responsible for the total suppression of excitonic emission, observed by photoluminescence (PL) spectroscopy.