Water's surface dielectric Theoretical studies predict that the inhibition of rotational motion of water near a solid surface will decrease its local dielectric constant. Fumagalli et al. fabricated thin channels in insulating hexagonal boron nitride on top of conducting graphene layers (see the Perspective by Kalinin). The channels, which varied in height from 1 to 300 nanometers, were filled with water and capped with a boron nitride layer. Modeling of the capacitance measurements made with an atomic force microscope tip revealed a surface-layer dielectric constant of 2, compared with the bulk value of 80 for water. Science, this issue p. 1339; see also p. 1302 Capacitance measurements reveal a low dielectric constant for atomically thin layers of water next to solid surfaces. 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.

中文翻译：

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承压水介电常数异常低

水的表面介电 理论研究预测，抑制固体表面附近水的旋转运动会降低其局部介电常数。富马加利等人。在导电石墨烯层顶部的绝缘六方氮化硼中制造薄通道（参见 Kalinin 的观点）。通道的高度从 1 纳米到 300 纳米不等，里面装满了水并用氮化硼层覆盖。使用原子力显微镜尖端进行的电容测量建模显示表层介电常数为 2，而水的体积值为 80。科学，这个问题 p。第1339章 另见第。1302 电容测量显示固体表面附近的原子级薄水层具有低介电常数。界面水的介电常数 ε 预计小于本体水的介电常数 (ε ≈ 80)，因为预计水偶极子的旋转自由度在接近表面会降低，但缺乏实验证据。我们报告了限制在两个原子级平坦壁之间的水的局部电容测量，这些壁之间的距离低至 1 纳米。我们的实验揭示了具有极小极化的界面层的存在，因此其面外 ε 仅为 ~2。发现电死层有两到三个分子厚。这些结果为描述水介导的表面相互作用和界面水行为的理论提供了急需的反馈，并提供了一种研究极端限制下其他流体和固体的介电特性的方法。