Gas molecules sandwiched in hydration layers at graphite/water interfaces

Abstract

Frequency shift-distance curves reveal that each adsorbed gas layer is sandwiched between hydration layers with high water density.

Zigzag gas phases on holey adsorbed layers

“…A clean glass syringe and steel needle were used to avoid contamination. 29 Moreover, we have conrmed in previous studies 19,21,30 that the domains nucleated by our procedure are indeed gases and not contamination.…”

“…36 It has been reported that the molecules constituting the ordered and disordered layers are immobile because of the strong interaction at the solid/gas interface, 16 resulting in solid-like behavior. 19,21 Because the stronglyadsorbed air molecules cannot diffuse on the surface to positions that make the local potential energy minimum, their growth regime is that of a self-affine random rough surface. 36 Consequently, the surface of the disordered layers becomes rough.…”

“…We proposed in our recent study that the ordered and disordered layers are stabilized by their connement in hydration structures constructed by the surrounding water molecules, such as gas hydrates. 21 Accordingly, the gas molecules at water/solid interfaces may become immobile relative to the water molecules at gas/solid interfaces, resulting in selfaffine rough growth.…”

“…[13][14][15] Furthermore, it has been revealed using AFM measurements that the accumulated gas molecules also form lm-like structures with a height of a few nanometers or less. These structures include epitaxially-ordered layers, 4,[16][17][18][19][20][21] disordered layers, 16,19,21 and micropancakes. 16,19,[22][23][24][25][26] Recent studies have reported that each gas structure is layered in the following order on the underlying substrate surface: ordered layers, disordered layers, and micropancakes.…”

“…19 Moreover, these layers have been shown to exhibit different vertical and horizontal mobility, which has been attributed to the differences in the magnitude of the attractive van der Waals forces from the solid surface 16,19 and connement in the hydration structures. 21 For the measurement of these atomically thin layers, frequency-modulation (FM)-AFM has been used because of its higher measurement sensitivity 4,16-21 than the more conventional amplitude-modulation (AM)-AFM. However, we recently revealed 19 that although FM-AFM can be used to observe the mobility of micropancakes, it cannot precisely measure their morphology because they are dragged by the AFM probe owing to its small oscillation amplitude (less than a few nanometers).…”