A New Conception of Evaporation and Condensation: Atomic Energies and the Impact on Thin Film Structure

原子蒸发时飞离表面的速度有多快？当它们接近一个表面时，它们会加速凝结吗？值得注意的是，这些问题还没有得到科学的回答。鉴于蒸发和冷凝现象在从大气科学到石油化学合成到薄膜涂层制造等领域的重要性，很明显，回答这些问题将具有最重要的科学意义。这项拟议中的研究将通过实验调查这些问题，并将首次提供明确的答案。利用真空中的机械速度选择器，我们将测量原子从热液体和固体表面喷射的速度分布。此外，我们将用速度过滤的蒸汽束凝结薄膜涂层，并研究动能对这些薄膜的结构和性质的影响。随着世纪热力学和物质动力学理论的发展，人们进行了一系列实验来验证气体的原子和分子确实表现出麦克斯韦-玻尔兹曼（MB）分布所预测的速度。首先是斯特恩在1920年，然后是埃尔德里奇在1927年，和Zartman在1931年，采用旋转速度过滤器来测量原子的速度分布从小孔径发射炉，都证实了预期的MB分布。动力学理论的准确性得到了证实，事实上，类似的装置已经被用于分子束领域的化学反应动力学研究，并已成为现代材料技术的核心，例如分子束外延。然而，他们都忽略了一点，那就是从烤箱中渗出的液体与从固体或液体表面直接弹道蒸发的液体完全不同。这项拟议的研究将利用现代实验技术研究弹道蒸发和冷凝中所涉及的原子能量。它将提供几个重要的当前问题的答案，例如，原子偏离弹道轨道，因为他们接近不断增长的薄膜表面？（“转向”）。我们还将开发利用速度过滤蒸汽制造纳米结构薄膜的技术。

How fast do atoms fly away from a surface as they evaporate? Do they accelerate as they approach a surface when they condense? Remarkably these questions have not yet been answered by science. Given the importance of evaporation and condensation phenomena in fields ranging from atmospheric science to petrochemical synthesis to thin film coating manufacturing it is clear that answering these questions will be of foremost scientific significance. This proposed research will experimentally investigate these questions and will, for the first time, provide definitive answers. Utilizing mechanical velocity selectors in vacuum we will measure the distribution of velocities of atoms ejected from hot liquid and solid surfaces. In addition we will condense thin film coatings with beams of velocity-filtered vapour and investigate the effect of kinetic energy on the structure and properties of these thin films. Following the development of thermodynamics and the kinetic theory of matter in the 19th century a series of experiments were conducted to verify that the atoms and molecules of gases do indeed exhibit the velocities predicted by the Maxwell-Boltzmann (MB) distribution. First Stern in 1920, then Eldridge in 1927, and Zartman in 1931, employed rotating velocity filters to measure the distribution of velocities of atoms emitted from small apertures in ovens, all confirming the expected MB distribution. The veracity of the kinetic theory was confirmed, and in fact similar apparatus have been employed since for the study of chemical reaction dynamics in the field of molecular beams, and have become a core modern materials technology, e.g. molecular beam epitaxy. What they have all missed, however, is that effusion from an oven is not at all the same as direct ballistic evaporation from a solid or liquid surface. This proposed research will examine the energies of atoms involved in ballistic evaporation and condensation utilizing modern experimental techniques. It will provide answers to several important current questions, e.g. are atoms deflected from ballistic trajectories as they approach a growing thin film surface? ("steering"). We will also develop technologies for manufacturing nanostructured thin films with velocity-filtered vapour.