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 de-adsorption 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.
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