Exceptional Surface Passivation Arising from Bis(trifluoromethanesulfonyl)-Based Solutions

The surface properties of many inorganic electronic materials (e.g., MoS2, WSe2, Si) can be substantially modified by treatment with the superacid bis(trifluoromethane)sulfonimide (TFSI). Here we find more generally that solutions based on molecules with trifluoromethanesulfonyl groups, including TFSI, give rise to excellent room temperature surface passivation, with the common factor being the presence of CF3SO2 groups and not the solution's acidity. The mechanism of passivation comprises two effects: (i) chemical passivation; and (ii) field effect passivation from a negatively charged thin film likely to be physically adsorbed by the surface. Degradation of surface passivation is caused by deadsorption of the thin film from the surface, and occurs slowly in air and rapidly upon vacuum exposure. The air stability of the passivation is enhanced by the presence of droplets at the surface which act to protect the properties of the film. The finding that nonacidic solutions can provide excellent electrical passivation at room temperature opens up the possibility of using them on materials more sensitive to an acidic environment.