Graphene Visualizes the First Water Adlayers on Mica at Ambient Conditions

Abstract

Icy Adsorption The highly mobile nature of adsorbed liquid water on surfaces has made structural studies using atomic force microscopy challenging, especially for the first adsorbed layer. Moreover, scanning probe methods are hindered by the strong interaction between the probe tip and the water molecules. When graphene flakes were deposited on mica, Xu et al. (p. 1188 ; see the Perspective by Katsnelson ) found that they could use atomic force microscopy to image the first and second layers of introduced water. They consistently observed an islandike structure—0.34 nanometers in height, at low humidity—that corresponded to a single layer of ice. At higher humidity, thicker layers with a more liquid nature were observed.

Evidence of Stranski–Krastanov growth at the initial stage of atmospheric water condensation

“…There are many water plateaus on the MoS 2 sample, and with sample-to-sample variations such island-like plateaus can also be observed in graphene samples even via tape-free mechanical exfoliation ( Supplementary Fig. 3), in agreement with previous reports 11,14,16 . The plateaus show no obvious difference in phase contrast with the surrounding elevated areas ( Supplementary Fig.…”

“…4), which indicates that these plateau structures occurred initially under both graphene and MoS 2 sheets, which further confirmed the sandwich arrangement as shown in Fig. 1b 11,14 .…”

“…In particular, the plateaus exhibited no obvious difference in phase contrast with the surrounding elevated areas, which may indicate that these plateau structures occurred under the graphene sheets ( Supplementary Fig. 4) 11,14 . Furthermore, at low coverage, the isolated island-like plateaus grew independently, whereas upon high water coverage they eventually coalesced into a continuous adlayer (Fig.…”

“…Different non-contact AFM and scanning polarization force microscopy methods have been developed to overcome many of these problems and have provided important results, but a disadvantage is that the large distance between the tip and the sample results in lower spatial resolution. Recently, graphene, albeit only one-atom thick, was found to not only prevent the evaporation of molecularly thin adlayers but also to act as an ideal template for studying the structures of ultrathin liquid adlayers on solid support under ambient conditions [10][11][12][13][14][15] . With the assistance of graphene, Xu et al 11 pioneered work on the observation of the first two ice-like water adlayers, increasing the humidity to 90%.…”

“…Recently, graphene, albeit only one-atom thick, was found to not only prevent the evaporation of molecularly thin adlayers but also to act as an ideal template for studying the structures of ultrathin liquid adlayers on solid support under ambient conditions [10][11][12][13][14][15] . With the assistance of graphene, Xu et al 11 pioneered work on the observation of the first two ice-like water adlayers, increasing the humidity to 90%. Similar phenomena have been reported between the interface of graphene and SiO 2 (hydrophilic substrate) 16 .…”