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arXiv · 1806.04486

Anomalously low dielectric constant of confined water

L. Fumagalli·A. Esfandiar·R. Fabregas·S. Hu·P. Ares·A. Janardanan·Q. Yang·B. Radha·T. Taniguchi·K. Watanabe·G. Gomila·K. S. Novoselov·A. K. Geim
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Abstract

The dielectric constant of interfacial water has been predicted to be smaller than that of bulk water (= 80) because the rotational freedom of water dipoles is expected to decrease near surfaces, yet experimental evidence is lacking. We report local capacitance measurements for water confined between two atomically-flat walls separated by various distances down to 1 nm. Our experiments reveal the presence of an interfacial layer with vanishingly small polarization such that its out-of-plane dielectric constant is only approximately 2. The electrically dead layer is found to be two to three molecules thick. These results provide much needed feedback for theories describing water-mediated surface interactions and behavior of interfacial water, and show a way to investigate the dielectric properties of other fluids and solids under extreme confinement.

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L. Fumagalli, A. Esfandiar, R. Fabregas, S. Hu, P. Ares, A. Janardanan, Q. Yang, B. Radha, T. Taniguchi, K. Watanabe, G. Gomila, K. S. Novoselov, A. K. Geim. 2018-06-12. Anomalously low dielectric constant of confined water. https://doi.org/10.1126/science.aat4191

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