Interfacial Gaseous States on Crystalline Surfaces

We previously reported formation of spherical-cap-shaped nanobubbles and a quasi-two-dimensional gas layer (micropancakes) on highly oriented pyrolytic graphite (HOPG) surfaces by the solvent-exchange protocol. Here we report that the same protocol is capable of inducing gaseous micropancakes as well as nanobubbles on two other crystalline surfaces: molybdenum disulfide (MoS2) and talc in water. The maximum height of gaseous micropancakes in atomic force microscopy (AFM) images was found to correlate well with the maximum height of nanobubbles on the same surface. In contrast, the same protocol was unable to induce spherical-cap-shaped nanobubbles or gaseous micropancakes on amorphous (glassy) carbon or on trimethylchlorosilane-coated silicon surfaces, which had a similar contact angle of water as the crystalline surfaces. It appears that formation of these interfacial gaseous states requires the presence of adequate nucleation sites on the surfaces (in addition to local supersaturation of gases created during the solvent exchange). The layered structure of the surfaces and concomitant presence of atomic steps appeared to have facilitated the formation of gaseous micropancakes.