Waterproof molecular monolayers stabilize 2D materials

Significance A family of strong yet removable 1- to 2-nm-thick ultrathin monolayer is developed as a corrosion inhibitor for 2-dimensional materials that significantly prolong lifetime while protecting optoelectronic properties in both ambient and harsh chemical or thermal environments. This method is low in toxicity and can be applied to arbitrary substrate with no size limit. Two-dimensional van der Waals materials have rich and unique functional properties, but many are susceptible to corrosion under ambient conditions. Here we show that linear alkylamines n-CmH2m+1NH2, with m = 4 through 11, are highly effective in protecting the optoelectronic properties of these materials, such as black phosphorus (BP) and transition-metal dichalcogenides (TMDs: WS2, 1T′-MoTe2, WTe2, WSe2, TaS2, and NbSe2). As a representative example, n-hexylamine (m = 6) can be applied in the form of thin molecular monolayers on BP flakes with less than 2-nm thickness and can prolong BP’s lifetime from a few hours to several weeks and even months in ambient environments. Characterizations combined with our theoretical analysis show that the thin monolayers selectively sift out water molecules, forming a drying layer to achieve the passivation of the protected 2D materials. The monolayer coating is also stable in air, H2 annealing, and organic solvents, but can be removed by certain organic acids.