Tip-Enhanced Raman Spectroscopy and Tip-Enhanced Photoluminescence of MoS2 Flakes Decorated with Gold Nanoparticles

Monolayers and a few layers of transition metal dichalcogenides (TMDs), organized as flakes or films, are notable for their electronic and optical properties, highlighting their interest for a variety of applications. Specifically, MoS2 flakes and films show a direct bandgap in their 2D form, which opens to applications in energy storage, optoelectronic devices, and in biosensing applications. Interestingly, hybrid systems composed of MoS2 flakes interfaced with metal nanoparticles, such as gold and silver, exploit the interplay between the interaction of plasmon of the metallic nanoparticle and the exciton of MoS2. Such plasmon–exciton interaction can be exploited to further improve the efficiency of TMD-based applications for sensing, catalysis, and photovoltaics. In this work, flakes of MoS2 grown on SiO2/Si substrates were prepared by chemical vapor deposition (CVD) under ambient pressure and were subsequently decorated using gold nanoparticles of distinct sizes. Tip-enhanced Raman spectroscopy and tip-enhanced photoluminescence measurements as well as contact potential difference (CPD) were conducted to evaluate the plasmon–exciton coupling of MoS2 flakes decorated with raspberry-like (∼100 nm) and seed-like (∼20 nm) gold nanoparticles.