Key Laboratory of Precision Microelectronic Manufacturing Technology & Equipment of Ministry of Education, Guangdong University of Technology, Guangzhou, 510006, China.
Nanoscale. 2017 Jul 13;9(27):9556-9561. doi: 10.1039/c7nr02176c.
Optical microscopy is the most direct method to probe fluid dynamics at small scales. However, contrast between fluid phases vanishes at ∼10 nm lengthscales, limiting direct optical interrogation to larger systems. Here, we present a method for direct, high-contrast and label-free visualization of fluid dynamics in sub-10 nm channels, and apply this method to study capillary filling dynamics at this scale. The direct visualization of confined fluid dynamics in 8-nm high channels is achieved with a conventional bright-field optical microscope by inserting a layer of a high-refractive-index material, silicon nitride (SiN), between the substrate and the nanochannel, and the height of which is accurately controlled down to a few nanometers by a SiO spacer layer. The SiN layer exhibits a strong Fabry-Perot resonance in reflection, providing a sharp contrast between ultrathin liquid and gas phases. In addition, the SiN layer enables robust anodic bonding without nanochannel collapse. With this method, we demonstrate the validity of the classical Lucas-Washburn equation for capillary filling in the sub-10 nm regime, in contrast to the previous studies, for both polar and nonpolar liquids, and for aqueous salt solutions.
光学显微镜是探测小尺度流体动力学最直接的方法。然而，在约 10nm 长度尺度下，流体相之间的对比度消失，限制了对更大系统的直接光学检测。在这里，我们提出了一种在亚 10nm 通道中直接、高对比度和无标记可视化流体动力学的方法，并应用该方法研究了该尺度下的毛细填充动力学。通过在基底和纳米通道之间插入一层高折射率材料氮化硅（SiN），并通过 SiO 间隔层将其高度精确控制在几纳米以下，从而在 8nm 高的通道中实现了对受限流体动力学的直接可视化。SiN 层在反射中表现出强烈的 Fabry-Perot 共振，在超薄膜和气相之间提供了鲜明的对比度。此外，SiN 层支持稳健的阳极键合，而不会导致纳米通道坍塌。通过这种方法，我们展示了经典的 Lucas-Washburn 方程在亚 10nm 范围内对毛细填充的有效性，与之前的研究相比，无论是极性和非极性液体，还是水盐溶液，都是如此。
