Layered Structures of Interfacial Water and Their Effects on Raman Spectra in Graphene-on-Sapphire Systems

Abstract

We investigated the structure of the interfacial water layers between graphene sheets and a sapphire substrate by observing them through graphene sheets at room temperature using atomic force microscopy. When graphene sheets were deposited at low relative humidity, the interfacial water layers appeared as small islands. They grew in layer-by-layer stacking with an increase in the relative humidity. We also investigated effects of the interfacial water layers on Raman spectra from the graphene sheets that cover the water layers. The correlation between G-peak position (intensity) and 2D-peak position (intensity) shows that the interfacial water induces hole-doping in graphene sheets. The doping density increases with increasing the amount of interfacial water. This study shows that the electrical properties of graphene sheets are tunable by controlling the hydrophilicity of substrate surfaces.

Prevention of Water Permeation by Strong Adhesion Between Graphene and SiO2 Substrate

“…The extent of doping is in good agreement with the experimentally found p‐doping caused by shifted Fermi energy and is also supported by the average blue‐shifted G peak values, which are approximately 5 cm −1 and 10 cm −1 for C‐BG and C‐NBG samples, respectively, as depicted in Figure d . However, although the shifted 2D peak values observed in this study are similar to those reported in the literature, they occur in the opposite direction; further research is thus required.…”

“…The lower I 2D /I G ratio of the C-NBG samples indicate more intense p-type doping in the C-NBG samples compared to the C-BG samples, because the 2D peak intensity diminishes as doping increases as a result of water permeation. The extent of doping is in good agreement with the experimentally found p-doping caused by shifted Fermi energy [ 36 ] and is also supported by the average blue-shifted G peak values, which are approximately 5 cm −1 and 10 cm −1 for C-BG and C-NBG samples, respectively, as depicted in Figure 4 d. [ 36 ] However, although the shifted 2D peak values observed in this study are similar to those reported in the literature, [ 36 ] they occur in the opposite direction; [ 37 ] further research is thus required.…”

“…When water molecules trapped under the graphene layer, it leads to p‐type doping of the graphene by a charge transfer from water to graphene. This doping gives rise to the more carrier concentration in graphene, and non‐adiabatically pushes the Fermi surface up or down depending on the type of carrier in electronic band.…”

Communication: Growing room temperature ice with graphene

“…5 The similitude in the measured heights on different surfaces has been ascribed to the reorganization of hydrogen bonding induced by the hydrophobic graphene sheet. 10 Note that the ice Ih BL structure is formed at RT, so that the term RT ice is fully justified. RT ice can be also prepared by applying external pressures, although in crystal structures different from ice Ih.…”

The role of ambient ice-like water adlayers formed at the interfaces of graphene on hydrophobic and hydrophilic substrates probed using scanning probe microscopy

“…It has been reported that the surface potential of graphene under ambient conditions is suppressed due to ambient adsorbates in comparison to graphene on SiO 2 under vacuum. 13 Verdaguer et al 26 studied the formation of interfacial water adlayers between FLG and insulating BaF 2 and CaF 2 substrates and found that the IWLs are formed only in the case of the BaF 2 substrate due to the less lattice mismatch with hexagonal (I h ) ice. 12,23 Lee et al 24 reported that under ambient conditions, first a stable bi-layer of ice-like structure is formed in between graphene and the SiO 2 substrate over a week of exposure, followed by liquid phase water formation upon one additional week of exposure, thereby introducing wrinkles and folds in graphene.…”