Physisorption Studies

摘要：提出了在石墨和其他衬底的均匀表面上研究多种吸附剂多层膜的热力学性质。在调节衬底温度的同时，椭偏仪将用于测量薄膜覆盖率作为气体压力的函数。这将提供关于微观润湿特性、分层、层临界点的直接信息，以及关于吸附质表面熔化的间接证据。将研究的吸附剂包括含有氢同位素分子的氘，以便与先前对氢分子、氮和一氧化碳的研究进行比较。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。通过吸附物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。除石墨外，衬底将包括金和氯化钠结构的离子晶体的劈裂面。非技术摘要：提出研究当原子光滑晶体表面（衬底）暴露于气体（吸附物）并与之平衡时，在其表面（衬底）上形成的一到几个分子层厚度的薄膜。底物包括石墨、氧化镁和其他晶体，而吸附剂包括氢、氮、一氧化碳、稀有气体和碳氢化合物。利用光学技术测量了薄膜厚度及其与气体压力和温度的关系。在低温下，由于连续分子层的加入，膜的厚度通常会急剧增加，直到达到可以形成吸附质宏观晶体的压力。这些研究提供了二维晶体热力学性质的信息，以及各种吸附物“润湿”衬底的能力，即在衬底上形成厚而均匀的薄膜。此外，在低于其整体熔化温度的温度下，将有可能测量吸附质晶体表面一层的粗化。＊＊＊

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. ***