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.

Supporting Information:Figure S1. Process flow schematics for the fabrication of graphene sheets.

Methods and Supplementary Figures Fig. S1. Contrast enhancement/optimization for different substrates.

Materials. Anhydrous inhibitor-free tetrahydrofuran (THF, ≥99.9%, water content <0.002%) and anhydrous cyclohexane (99.5%, water content <0.001%) were purchased from Sigma-Aldrich. These reagents were used as supplied and stored in a glove-box purged with nitrogen. Muscovite mica (Grade V1; round disks of diameter 10 mm) was obtained from Ted Pella. Kish graphite was obtained from Covalent Materials US Inc.Sample preparation. Samples were prepared in a glove-bag (Sigma-Aldrich AtmosBag) that was purged and protected under a continuous flow of ultra-high purity argon, in which the relative humidity (RH) was controlled to be <2%. Humidity was monitored using a Fluke 971 temperature humidity meter. All experiments were performed at room temperature (22±2 °C). Mica disks were first heated in air at 200 °C for 10 min to remove absorbed moisture, and then transferred into the glove-bag. The mica surface was cleaved in the glove-bag and exposed to organic vapors for ~10 s to ~1 min. The partial pressure of organic molecules at the mica surface, which determines the surface coverage at equilibrium, was adjusted by varying the distance between the vapor source and the mica surface. Graphene sheets were deposited onto the mica surface through the standard method of mechanical exfoliation (Novoselov et al. 2005; Lui et al. 2009) of Kish graphite, thus sealing and preserving the adlayers of organic molecules.Identification of graphene layers. Monolayer graphene sheets were identified through optical microscopy and confirmed by spatially resolved Raman spectroscopy (Xu et al. 2010). Raman spectra were recorded with a Renishaw M1000 Micro Raman spectrometer system using a 514.5 nm laser beam and a 2400 lines per mm grating. A confocal optical microscope with a ×100 objective lens was used to record spectra with a spatial resolution of 2 μm. No noticeable D peak was observed in the Raman spectra (Fig. S1), indicating high-crystalline order of our samples.Atomic Force Microscopy. All AFM images were acquired under tapping mode on a Digital Instrument Nanoscope IIIA at ambient conditions. A sharp TESP tip (Veeco) with a radius of end of 8 nm was used. Typical values for the force constant and resonance frequency were 42 N/m and 320 kHz respectively. Height calibrations were performed using the step heights of freshly cleaved graphite samples. Due to the super-flatness of the samples, sometimes the laser interference pattern along the slow-scan axis was hard to avoid, which is more noticeable in large-area scanning and have a period of twice the wavelength of the laser. This is caused by the constructive interference of laser reflected from the sample surface and

Supporting Information MethodsAu(111)/mica substrates (1.4 cm × 1.1 cm; gold thickness: 150 nm) were purchased from SPI. A sealed container containing the Au(111)/mica substrate was opened in a N 2 /water vapor purged glovebag with controlled RH of 40%. The substrate was allowed to equilibrate with the environment for ~5 min, and then graphene sheets were deposited onto the Au(111) surface by mechanical exfoliation of Kish graphite.Thin graphene flakes were first searched for under an optical microscope. Few-layer (<3) graphene was hard to identify on the Au surface, but often appeared around the edges of thicker graphite flakes that can be more readily observed on the surface ( Figure S1). To locate and confirm the few-layer graphene areas, AFM was subsequently performed under tapping mode on a Digital Instrument Nanoscope IIIA. STM studies were carried out using an Omicron LT-STM operating under ultrahigh vacuum (<10 -10 torr) at both room temperature and 77 K. Figure S1