Structure of the Interfacial Properties of Helium-3, Helium-4, and Helium-3/Helium-4 Mixtures: X-ray Scattering Studies

本项目采用x射线散射方法测量了3He、4He和3He - 4He混合物在一定温度和组成范围内以及各种外部控制几何形状下的界面结构。从理论角度来看，氦界面很有趣，因为它们代表了一个定义良好的、宏观定向的、非均匀量子流体的相对罕见的实现。体氦的超流体性质从根本上取决于液体密度。然而，要大幅度改变堆积密度是极其困难的。相反，液体/蒸汽界面上的密度从均匀体积值变化到基本为零。x射线实验是目前对现有理论的唯一测试，这些理论预测了量子流体混合物的结构变化。此外，还可以测量可以稳定在氦表面上的二维电子流体的平面内相关性。如果成功，这将提供一种工具来表征二维维格纳晶格的结构和位置相关性，这些晶格是由氦表面成像势中捕获的电子层形成的。在表面物理和流体动力学领域，这些实验具有基本的兴趣，并将引起更广泛的兴趣。该项目采用x射线散射方法测量了3He、4He和3He - 4He流体混合物在一定温度和成分范围内以及各种外部控制几何形状下的界面结构。这些低温流体具有许多与它们的“超流动性”有关的新性质。形成表面层的原子排列将通过使用来自同步加速器光源的x射线束的x射线方法来确定。在另一个子项目中，有可能在氦的表面捕获电子薄膜。电子在这一层的排列也将被寻求。在表面物理和流体动力学领域，这些实验具有基本的兴趣，并将引起更广泛的兴趣。＊＊＊

9523281 Pershan This project employs x-ray scattering methods to measure the interfacial structures of 3He, 4He and 3He - 4He mixtures over a range of temperatures and composition, and under a variety of externally controlled geometries. The helium interfaces are interesting from a theoretical view because they represent the relatively rare realization of a well-defined, macroscopically oriented, inhomogeneous quantum fluid. The superfluid properties of bulk helium are fundamentally dependent on the liquid density. However, it is extremely difficult to vary the bulk density by significant fraction. In contrast, the density across the liquid/vapor interface varies from the uniform bulk value to essentially zero. The x-ray experiments are currently the only test of extant theories of the structural changes anticipated for mixture of the quantum fluids. In addition, it may be possible to measure the in-plane correlations for the two-dimensional electron fluid that can be stabilized on the surface of the helium. If successful, this would provide a tool to characterize the structure and positional correlations of the two-dimensional Wigner lattice formed by the layer of electrons trapped in the image potential at the helium surface. The experiments are of fundamental interest and will be of wider interest in the field of surface physics and fluid dynamics. %%% This project employs x-ray scattering methods to measure the interfacial structures of 3He, 4He and 3He - 4He fluid mixtures over a range of temperatures and composition, and under a variety of externally controlled geometries. These cryogenic fluids have many novel properties related to their "superfluidity". The arrangements of atoms forming the surface layers will be determined by x-ray methods using a beam of x-rays from a synchrotron light source. In another sub-project, it is possible to trap a film of e lectrons on the surface of the helium. The arrangement of electrons in this layer will also be sought. The experiments are of fundamental interest and will be of wider interest in the field of surface physics and fluid dynamics. ***