Physisorption Studies

9320860 Hess技术摘要：建议研究在石墨和其他衬底的均匀表面上的多层膜的热力学性质。椭偏仪将被用来测量薄膜覆盖率作为气体压力的函数，而衬底温度是调节的。这将提供有关微观润湿性质、分层、分层临界点的直接信息，以及关于吸附物表面熔化的间接证据。将被研究的吸附物包括含有氢的同位素分子的氢，以便与以前关于分子氢、氮和一氧化碳的工作进行比较。将重点研究气体混合物在薄膜中的溶解度和预镀层的位移。通过吸附振动模式的红外吸收将提供关于薄膜组成和分子取向的额外信息。除了石墨外，衬底还将包括金和氯化钠结构的离子晶体的解理面。非技术摘要：有人建议研究在原子光滑的晶体表面(衬底)上形成的一到几个分子层厚度的薄膜，当它暴露在气体(吸附物)中并与之平衡时。衬底将包括石墨、氧化镁和其他晶体，而吸附物包括氢、氮、一氧化碳、稀有气体和碳氢化合物。用光学技术测量了薄膜厚度及其与气压和温度的关系。在低温下，由于连续的分子层的添加，薄膜厚度通常会急剧增加，直到达到可以形成吸附物宏观晶体的压力。这些研究提供了有关二维晶体的热力学性质的信息，以及各种吸附物质对衬底“润湿”的能力，即在衬底上形成厚厚的均匀薄膜的能力。此外，还可以在低于其整体熔化温度的温度下测量吸附晶体表面的一层粗糙度。***

9320860 Hess Technical abstract: It is proposed to study the thermodynamic properties of multilayer films of a number of adsorbates on uniform surfaces of graphite and other substrates. Ellipsometry will be used to measure the film coverage as a function of gas pressure, while the substrate temperature is regulated. This will provide direct information on microscopic wetting properties, layering, layer critical points, and indirect evidence regarding surface melting of the adsorbate. Adsorbates which will be studied include deuterium containing isotopic molecules of hydrogen, for comparison with previous work on molecular hydrogen, nitrogen and carbon monoxide. Gas mixtures will be studied with emphasis on solubility in films and displacement of pre-plated layers. Infrared absorption by adsorbate vibrational modes will provide additional information on the film composition and molecular orientation. Substrates in addition to graphite will include gold and cleaved faces of ionic crystals of the sodium chloride structure. Non-technical abstract: It is proposed to study films of one to a few molecular layers in thickness formed on an atomic smooth crystal surface (the substrate) when it is exposed to, and in equilibrium with, a gas (the adsorbate). Substrates will include graphite, magnesium oxide, and other crystals, while the adsorbates include hydrogen, nitrogen, carbon monoxide, rare gases, and hydrocarbons. An optical techniques is used to measure the film thickness and its dependence on gas pressure and on temperature. At low temperatures the film thickness typically increases in sharp steps due to the addition of successive layers of molecules, until the pressure is reached at which macroscopic crystals of the adsorbate can form. These studies provide information on the thermodynamic properties of two-dimensional crystals, and the ability of various adsorbates to "wet" the substrates, that is, to form thick uniform films on them. In addition, it will be possible to measure roughening of a layer at the surface of adsorbate crystals at temperatures below their bulk melting temperature. ***