Two-Dimensional Water Diffusion at a Graphene–Silica Interface

Abstract

Because of the dominant role of the surface of molecules and their individuality, molecules behave distinctively in a confined space, which has far-reaching implications in many physical, chemical, and biological systems. Here we demonstrate that graphene forms a unique atom-thick interstitial space that enables the study of molecular diffusion in two dimensions with underlying silica substrates. Raman spectroscopy visualized intercalation of water from the edge to the center underneath graphene in real time, which was dictated by the hydrophilicity of the substrates. In addition, graphene undergoes reversible deformation to conform to intercalating water clusters or islands. Atomic force microscopy confirmed that the interfacial water layer is only ca. 3.5 Å thick, corresponding to one bilayer unit of normal ice. This study also demonstrates that oxygen species responsible for the ubiquitous hole doping are located below graphene. In addition to serving as a transparent confining wall, graphene and possibly other two-dimensional materials can be used as an optical indicator sensitive to interfacial mass transport and charge transfer.

Role of residual polymer on chemical vapor grown graphene by Raman spectroscopy

“…The fact that doping value maintains in the presence/absence of PMMA indicates that the contact between protruding SiO 2 features and graphene is main contributor to doping and PMMA has negligible effect. Similar trend has been observed in single-walled carbon nanotube (SWNT) [42][43][44]: while SWNT on quartz substrate does not have or weak photoluminescence (PL) [43,45], SWNT embedded in PMMA [44] or on sapphire [45] displays strong PL. This is attributed to significant doping effect of SiO 2 compared to neural PMMA or basic sapphire.…”

Imaging Water Thin Films in Ambient Conditions Using Atomic Force Microscopy

“…First, that water layers coated by graphene still interact with water molecules on the environment because water molecules can adsorb and desorb through graphene edges and cracks [57,58]. That implies that processes of wetting and dewetting can happen below the graphene layer depending on environmental [59,60] and temperature conditions [61]. This fact has been used to study also the evolution of water films between a substrate and graphene as a function of temperature.…”

The influence of two-dimensional organic adlayer thickness on the ultralow frequency Raman spectra of transition metal dichalcogenide nanosheets

“…Moreover, the sandwiched ultrathin water film can strongly decrease the PL of monolayer MoS 2 by a factor of 30-50, which was attributed to trion formation [29,34]. In addition, the morphology of confined water played an important role in affecting the electronic structure of MoS 2 [30]. Atomically thin water film was considered as n-type dopant while trapped water droplet acted as p-type dopant [29].…”