In contrast to surface nanobubbles, the properties of atomically flat gas phases such as micropancakes remain unclear. In this study, we investigated nanoscopic gas phases existing at the interface between highly ordered pyrolytic graphite and air-supersaturated pure water using high-sensitivity frequency-modulation atomic force microscopy (AFM). Micropancakes appeared on a disordered gas layer overlying an ordered gas layer and moved in the direction of AFM scanning. Their movement stopped at the edge of the disordered gas layers, whereas the two gas layers did not move at all. The limited mobility of micropancakes is explained by assuming that the disordered and ordered gas layers, which are composed of strongly adsorbed gas molecules, behave like solid surfaces, and that the surface heterogeneity between them results in a pinning effect.
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