International Research Fellowship Program: Investigation of Nanoscale Water Columns using a MEMS Force Sensor

该奖项由2009年美国复苏和再投资法案(公法111-5)资助。国际研究奖学金计划使美国科学家和工程师能够在国外进行9至24个月的研究。该项目的奖项提供了联合研究的机会，并利用国外独特或互补的设施、专业知识和实验条件。该奖项将支持Corey A.Stambaugh博士与韩国首尔国立大学的JHE Wonho博士和美国佛罗里达大学的Ho Bun Chan博士合作为期24个月的研究奖学金。液体在各种现象中发挥着重要作用。尤其是水，是生命的基础。然而，尽管如此，它的一些性质以及液体的性质总体上仍然没有得到很好的了解。当液体样品被限制在空间尺寸为纳米级的空间时，情况尤其如此。在这里，水已经被发现表现出许多有趣和新奇的特征，包括冰相的表现，这在大块样品中是不常见的，并显示出固体般的有序。两个表面之间的薄薄的纳米水层是日常摩擦的原因，也是摩擦学中许多现象的背后原因。纳米水在蛋白质折叠和酶激活等生物过程中也发挥着重要作用。不幸的是，由于散装水的短程有序和水分子的持续搅拌，这些特征在大多数情况下被证明是很难研究的。近年来，纳米技术的进步使得在越来越小的长度范围内制造和探测系统成为可能。这些进展为在纳米尺度上研究液体样品提供了手段。首尔国立大学的Wonho Jhe教授最近使用原子力显微镜研究了小空间中纳米尺度水柱的形成。这些研究表明，纳米尺度的水样实际上具有弹性性质；这一特征被在大块水样中观察到的粘性性质所掩盖。这项研究的重点是从实验上探索纳米液柱的性质，特别是水的性质。这是通过结合两种实验技术来测量力梯度和纳米级水柱施加的力来实现的。第一种技术涉及使用原子力显微镜测量通过小幅度调制方法操作的力梯度。第二种是使用灵敏的微型机电(MEMS)力传感器来测量柱子施加的力。这两种技术的结合为研究原子力显微镜、S悬臂梁和MEMS力传感器之间形成的纳米水柱的若干特性提供了一种新的方案。具体包括湿度对粘附力的影响，水的弹性和粘度，以及毛细管凝结的松弛和成核时间。这些结果将有助于我们理解纳米水在生物过程中所起的作用，以及粘附力对扫描探针显微镜和MEMS性能的影响。

0853104StambaughThis award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad.This award will support a twenty-four-month research fellowship by Dr. Corey A. Stambaugh to work with Dr. Jhe Wonho at Seoul National University in Korea and with Dr. Ho Bun Chan at the University of Florida in the US.Liquids play an important role in a variety of phenomena. Water, in particular, is fundamental to life. Yet despite this, several of its properties and those of liquids, in general, are still not well understood. This is especially true when the liquid samples are confined to spaces whose spatial dimensions are on the nanoscale. Here, water has been found to exhibit many interesting and novel features including the manifestation of ice phases, not typically seen in bulk samples and exhibition of solid-like orderedness. Thin nanometer layers of water between two surfaces are responsible for every day experiences with friction and are behind many of the phenomena seen in tribology. Nanoscale water also plays an essential role in biological processes such as protein folding and enzyme activation. Unfortunately, due to the short-range order of bulk water and constant agitation of water molecules, these features prove difficult to investigate under most circumstances. In recent years, advances in nanotechnology have allowed for the fabrication and probing of systems on increasingly smaller length scales. Such advances have provided the means to study liquid samples on the nanoscale. Recent work by Prof. Wonho Jhe at Seoul National University examined the formation of nanoscale water columns in small spaces using an atomic force microscope. These studies have shown that nanoscale water samples actually possess elastic properties; a feature obscured by the viscous properties observed in bulk water samples. This research focuses on experimentally probing the properties of nanoscale liquid columns, specifically water. This is done by combining two experimental techniques to measure both the force gradient and the force exerted by the nanoscale water columns. The first technique involves measuring the force gradient operated via the small amplitude-modulated method using an atomic force microscope. The second uses a sensitive microelectromechanical (MEMS) force sensor to measure the forces exerted by the columns. The combination of the two techniques provides a novel scheme for studying several features of the nanoscale water columns that are formed between the atomic force microscope?s cantilever and the MEMS force sensor. The specific features include the impact of humidity on the adhesive force, the elasticity and viscosity of water, and the relaxation and nucleation time of capillary condensation. These results will contribute to our understanding of the role nanoscale water can play in biological processes and of the effect the adhesive force has on the performance of scanning probe microscopy and MEMS.