MX2 cleaning by combination liquid solvent and plasma ashing

Monolayer MX₂ (transition metal dichalcogenides) are considered as alternative channel materials for advanced CMOS devices. The construction of CMOS transistors requires to clean the MX₂ film multiple times, using various (wet) chemicals. It has been observed recently that the contact of the 2D layer with solvent is inducing major changes in their optical response (photoluminescence, Raman peaks) but also in their transport properties (I_on/I_off, mobility, etc...). The interplay between dry cleaning (using remote plasma clean for instance) and wet cleans has also been highlighted as a source of MX₂ modification, which need to be better understood and controlled.

In this internship, we will study the impact of various post-processing treatments on the synthetic, MOCVD grown WS₂ monolayers. Various solvents and/or diluted chemistries will be used to treat the WS₂ films, varying concentration, additives, temperature, dip time and surface pre-treatments (H₂ plasma, UV-O₃). The quality of the WS₂ monolayers will be studied by means of photoluminescence, AFM, XPS, WCA. Transport properties will be tentatively studied using ion gel gating. The long-term objective is to establish a link between the physico-chemical properties of the solvents and the changes induced on the WS₂ films. The short-term objective is to determine which solvents or diluted acid/base are damaging the WS₂ films.