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Crossover of 2- and 3-dimensional critical phenomena on mercury-sapphire interface

汞-蓝宝石界面上 2 维和 3 维临界现象的交叉

基本信息

批准号：
16540314
负责人：
OHMASA Yoshinori
金额：
$ 2.37万
依托单位：
Kyoto University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2005
项目状态：
已结题

项目摘要

It is well known that liquid mercury hardly wets non-metallic substances such as glasses or sapphire under ambient conditions. However, mercury wets sapphire substrate under high temperature and pressure conditions near the liquid-gas critical point (1478℃、167MPa), and the thickness of the wetting film jumps discontinuously at a line on the pressure-temperature plane. This is the 1st order phase transition called the prewetting (PW) transition. In the present work, we studied the static and dynamic properties of the wetting film by using optical methods such as (1) optical reflectivity, (2) optical emissivity, (3) static light scattering and (4) dynamic light scattering, and tried to unveil the crossover between the 2-and the 3-dimensional critical phenomena.From the static light scattering, we observed that diffuse scattering appears around the specularly reflected light spot when the wetting film is present. Interestingly, this diffuse scattering is strong along the vertical directio … More n, and weak along the horizontal direction. This result indicates that the gravity plays important role on the structure of the light scatterer in the wetting film. In the PW transition region, there exist contact lines between the thick and the thin wetting films, and the gravity makes the contact lines aligned along the horizontal direction, resulting in the strong diffuse scattering along the vertical direction. From the dynamic light scattering, we observed intermittent fluctuations in the scattering intensity, and these fluctuations are interpreted to be caused by the movement of the contact line across the laser light spot. We estimated the velocity of the contact line, and found that the contact line moves mainly along the vertical direction.As a related study, we studied the wetting phenomena of selenium-thallium mixtures on a quartz substrate. This system transforms from semiconductor to metal with increasing thallium concentration, and has a similarity to mercury, which shows metal-nonmetal transition with decreasing density. Surprisingly, "critical point dewetting" phenomena was observed : the wetting film is not formed near the critical temperature but is formed in the lower temperature region. This is completely opposite to the Cahn's prediction of "critical point wetting" and is very interesting phenomena. Less

众所周知，液态汞在环境条件下几乎不湿润玻璃或蓝宝石等非金属物质。然而，在高温高压条件下，汞在液气临界点（1478℃，167MPa）附近润湿蓝宝石衬底，润湿膜厚度在压力-温度平面上呈不连续的直线跳变。这是一阶相变，称为预润湿（PW）相变。本文采用光学方法(1)光反射率、(2)光发射率、(3)静态光散射和(4)动态光散射等方法研究了湿膜的静态和动态特性，并试图揭示二维和三维临界现象之间的交叉。从静态光散射中，我们观察到当湿膜存在时，在镜面反射光斑周围出现漫射散射。有趣的是，这种扩散散射在垂直方向上很强，而在水平方向上很弱。这一结果表明，重力对湿膜中光散射体的结构有重要影响。在PW过渡区，厚膜和薄膜之间存在接触线，重力使接触线沿水平方向排列，导致沿垂直方向产生强烈的漫射散射。从动态光散射中，我们观察到散射强度的间歇性波动，这些波动被解释为由接触线在激光光斑上的运动引起的。我们估计了接触线的速度，发现接触线主要沿垂直方向移动。作为一项相关研究，我们研究了硒-铊混合物在石英衬底上的润湿现象。该体系随着铊浓度的增加从半导体向金属转变，与汞相似，随着密度的降低呈现金属向非金属的转变。令人惊讶的是，观察到“临界点脱湿”现象：在临界温度附近没有形成润湿膜，而是在较低温度区域形成。这与卡恩的“临界点润湿”预测完全相反，是一个非常有趣的现象。少