Fig. 1: Broadband dielectric imaging of nanoconfined water.
From: In-plane dielectric constant and conductivity of confined water
a, Schematic of the experimental set-up and our devices. The hBN top, bottom and spacer layers are shown in light blue and the graphite ground electrode is shown in black. The water is filled from a back-side inlet (Extended Data Fig. 1d). Oscillating voltage (f from 0.1 kHz to 1.1 GHz) is applied to the AFM tip and the measured local impedance is converted into dielectric spectra such as that shown schematically in the inset. Relatively thick bottom hBN (H ≈ 50–200 nm) is used to create in-plane field E// inside water channels. b, AFM micrograph of a device with h ≈ 30 nm, with the inset showing a trace over the exposed spacers. c,d, Dielectric images at characteristic f of 2 kHz, 2 MHz and 1.1 GHz for the same three channels before and after filling them with water, respectively. The images were taken at 295 ± 1 K from the area outlined in b by the dashed rectangle. The top panels in c and d sketch the cross-section of the channels (not to scale). The slight sagging of the top hBN into empty channels disappears after filling them with water. The sagging was monitored by AFM to ensure that the channels were fully filled22. e, Dielectric profiles (averaged over ten lines) from c and d, colour-coded. |dC/dz| is defined in Methods. Scale bars: 1 μm (b); 500 nm (c,d).
