Scanning Ripplon Microscopy

朗缪尔膜是一种在水面上膨胀的分子单层膜，是LB膜的重要材料，具有多种工业应用。该薄膜显示了二维气相、液相和固相之间的相变，也引起了纯粹的物理兴趣。在我们之前的研究中，我们已经建立了一种非接触测量波纹的“宽带波纹光散射技术”，即波纹光散射。高频毛细波在水面上的热激发和传播。该技术已应用于研究Langmuir薄膜的分子动力学；揭示了膜的局部结构、不均匀性和缩合状态。本研究的目的是通过提高这种光散射技术的空间分辨率，并将其与表面扫描系统相结合，开发出一种“涟漪显微镜”。通过测量表面能和表面粘弹性这两个敏感反映水表面单分子层状态的数值，有助于对膜的定量评价。这为朗缪尔薄膜的结构分析提供了一种非常有效的手段。我们还打算阐明LB膜的功能是如何由作为其材料的朗缪尔膜的结构和动力学决定的。本研究对该技术的信号处理和光学系统进行了改进；并构建了一个表面扫描系统。我们成功地以-10微米的空间分辨率和精度可视化了表面结构。我们将新系统应用于研究二维物理的各种效应，包括热膨胀和相变。这些结果告诉我们一个有趣的事实，二维物质和我们熟悉的三维物质一样，也有临界现象，它们的行为是在平均场理论的框架内描述的。

Langmuir film, a monolayr of molecules expanded on water surface, is important as a material for the LB film which has various industrial applications. The film shows phase transitions among two-dimensional gas, liquid and solid phases, and has attracted also a pure physical interest. In our previous studies we had established "Wide-band ripplon light scattering technique" for a non-contact measurement of ripplon, ie. high-frequency capillary waves thermally excited and propagating on water surface. This technique has been applied for investigating molecular dynamics in the Langmuir films ; local structure of the film, inhomogenuity and state of condensation have been revealed.The purpose of the present study is to develop "a ripplon microscope" by increasing spatial resolution of this light scattering technique and combining it with a surface scanning system. It would be useful for quantitative evaluation of the films by measuring the surface energy and the surface visco-elasticity, the values which sensitively reflect the state of monomolecular layr on water surface. It would provide us with a very effective means for structure analysis of Langmuir films. We also intended to clarify how the function of a LB film is determined by the structure and dynamics of the Langmuir film as its material.In this study we improved the signal processing and the optical system of the technique ; and constructed a surface scanning system. We succeeded in visualizing the surface structure with -10 mum spatial resolution and precision. We applied the new system for studying various effects of two-dimensional physics, including thermal expansion, and phase transitions. These results taught us an interesting fact two-dimensional substances also have critical phenomena as the more familiar three-dimensional ones, and their behavior is described within a framework of the mean field theory.