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

doi:10.1126/science.aat4191

Anomalously low dielectric constant of confined water

Science. 2018 Jun 22;360(6395):1339-1342. doi: 10.1126/science.aat4191.

Authors

L Fumagalli^{1

2}, A Esfandiar³, R Fabregas^{4

5}, S Hu^{6

2}, P Ares^{6

2}, A Janardanan^{6

2}, Q Yang^{6

2}, B Radha^{6

2}, T Taniguchi⁷, K Watanabe⁷, G Gomila^{4

5}, K S Novoselov^{6

2}, A K Geim^{1

2}

Affiliations

¹ School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK. laura.fumagalli@manchester.ac.uk geim@manchester.ac.uk.
² National Graphene Institute, University of Manchester, Manchester M13 9PL, UK.
³ Department of Physics, Sharif University of Technology, P.O. Box 11155-9161, Tehran, Iran.
⁴ Departament d'Electrònica, Universitat de Barcelona, C/ Martí i Franquès 1, 08028 Barcelona, Spain.
⁵ Institut de Bioenginyeria de Catalunya, Barcelona Institute of Science and Technology, C/ Baldiri i Reixac 15-21, 08028 Barcelona, Spain.
⁶ School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK.
⁷ National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.

PMID: 29930134
DOI: 10.1126/science.aat4191

Abstract

The dielectric constant ε of interfacial water has been predicted to be smaller than that of bulk water (ε ≈ 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 nanometer. Our experiments reveal the presence of an interfacial layer with vanishingly small polarization such that its out-of-plane ε is only ~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 the behavior of interfacial water, and show a way to investigate the dielectric properties of other fluids and solids under extreme confinement.