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. ***
