Development of a Dynamic Helium Atom Scattering Apparatus to Probe Nanoscale Surface Fluctuations

现代材料研究的大多数领域基本上集中在纳米尺度上的能量相互作用上，但这种相互作用仍然表现在不寻常的宏观材料特性上。虽然有许多技术可用于探测材料的静态微观特性，但很少有技术提供确定微观和宏观世界之间相互作用的动态模式的中等时间尺度（1 ms - 1 s）特征的微观信息。因此，迫切需要开发结合高空间和时间分辨率的新技术。Kevan教授和他的合作者将建造一种新的装置来产生横向相干氦原子束。他们将开发类似于动态激光散射的方法，并应用这些方法在短至几纳米的长度尺度和短至一微秒的时间尺度上研究表面波动。应用这种新技术研究的现象包括：1)表面物质扩散的基本步骤；2)导电和非导电聚合物和自组装单层膜的平衡和稳态表面波动；3)高温超导体自旋电荷分离相的波动。PI正在开发一种氦原子散射装置，用于探测纳米级的表面波动。现代材料研究的一个重点是控制材料的结构，以了解并最终控制其功能。理解结构需要测量原子在空间中是如何排列的，以及它们是如何相互结合形成分子和固体的。这与材料的静态特性有关。相比之下，理解功能需要测量材料是如何运作的，无论是机械的、化学的、电的还是磁的。函数本质上是一个动态概念。虽然有许多结构技术——例如各种显微镜和x射线衍射——但只有相对较少的技术能够在从几个原子到许多原子的长度尺度上提供关于材料动力学特性的深刻信息。许多关键技术依赖于这种规模的人造材料，这使得开发这种技术迫在眉睫。在这里，研究人员正在开发一种氦原子的新用途，试图解决这一需求。像x射线一样，氦原子可以探测非常短的维度。该仪器将产生高度准直的原子束，具有一些类似激光的特性。这将允许应用类似激光的动力学技术，但对原子尺度的尺寸敏感。

Most areas of modern materials research focus fundamentally on energetic interactions that operate on the nanometer length scale but which nonetheless are manifested in unusual macroscopic material properties. While many techniques are available to probe the static microscopic properties of materials, few provide microscopic information on the moderate time scales (1 ms - 1 s) characteristic of dynamical modes that determine the interplay between microscopic and macroscopic worlds. There is therefore an urgent need to develop new techniques that combine high spatial and temporal resolution. Professor Kevan and his co-investigators will construct novel apparatus to produce a transversely coherent helium atom beam. They will develop methodologies analogous to dynamic laser light scattering and apply these to study surface fluctuations at length scales as short as a few nanometers and on time scales as short as one microsecond. Examples of phenomena to be studied using this new technique include 1) the elementary steps in diffusion of surface species, 2) equilibrium and steady-state surface fluctuations in conducting and non-conducting polymer and self-assembled monolayer films, and 3) the fluctuations of high temperature superconductors in the spin-charge segregated phase. The PI is developing a helium atom scattering apparatus, to probe nanoscale surface fluctuations. A key focus of modern materials research is to control a material's structure in order to understand and ultimately control its function. Understanding structure requires measuring how atoms are arranged in space and how they are bonded to each other to form molecules and solids. This pertains to a material's static properties. By contrast, understanding function requires measuring how a material operates, either mechanically, chemically, electrically, or magnetically. Function is intrinsically a dynamical concept. While there are many structural techniques - various microscopes and x-ray diffraction, for example - there are only relatively few that provide incisive information about a material's dynamical properties on a length scale ranging from a few to many atoms. That many key technologies rely on materials that are artificially patterned on this scale makes it urgent to develop such techniques. Here the investigators are developing a novel use for helium atoms to try to address this need. Like x-rays, helium atoms can probe very short dimensions. The instrument will produce a very highly collimated beam of atoms that will have some laser-like properties. This will allow application of laser-like dynamical techniques, but with sensitivity to sizes on the scale of atoms.