Metal vapor interface

The dissociation of an isolated water molecule occurs via the insertion of metal atom into one of its 0-H bonds. As the 0-H bond is initially activated, the energy level of the unoccupied a antibonding 0-H orbital lowers, thus allowing for electron transfer from the metal into this state. This subsequently facilitates the activation of water. Dissociation of an isolated water molecules adsorbed from the gas phase at the metal/vapor interface leads to the formation of a surface hydroxyl as well as a surface hydride. Desai and NeurockI showed that the activation of water over Pt(lll) would be highly endothermic (-1-90... 

For a pure liquid metal, we may write the excess surface energy, E of the liquid metal-vapor interface, as... 

ADSORPTION AND ELECTRICAL PROPERTIES OF LIQUID METAL/VAPOR INTERFACES... 

Keywords Metal vapor deposition Metal-organic interface Molecular devices Molecular electronics Self-Assembled Monolayers... 

The screening is being done in 98 w/o sulfuric acid. Materials samples are placed in the liquid and vapor phases of the test vessel, as well as at the liquid/vapor interface. Typical test results are shown in Figures 10, 11, and 12. As is apparent, commercially available metallic alloys do not appear to be able to survive the operating environment. Silicon containing materials, however, used as structures or protective coatings on metallic alloys, appear to have promise of fulfilling the process needs. 

The problem of adhesion between a polymer and a metal is strongly dependent on the specific type of polymer and metal involved, as well as on the deposition process under which the interface between the two is formed. In order to improve adhesion, different pretreatment methods can be used, but the development of such techniques requires detailed information about metal-polymer interfaces. Particularly, in the case of thin metal films deposited by physical vapor deposition (PVD) in ultra high vaccum (UHV), X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) have been used to obtain chemical information about initial film growth modes,... 

In order make an effort to bring the polyimide-metal adhesion problem to an even more fundamental level, we have previously proposed that model molecules, chosen as representative of selected parts of the polyimide repeat unit, may be used to predict the chemical and electronic structure of interfaces between polyimides and metals (12). Relatively small model molecules can be vapor deposited in situ under UHV conditions to form monolayer films upon atomically clean metal substrates, and detailed information about chemical bonding, charge transfer and molecular orientation can be determined, and even site-specific interactions may be recognized. The result of such studies can also be expected to be relevant in comparison with the results of studies of metal-polymer interfaces. Another very important advantage with this model molecule approach is the possibility to apply a more reliable theoretical analysis to the data, which is very difficult when studying complex polymers such as polyimide. 

Understanding chemical reactivity at liquid interfaces is important because in many systems the interesting and relevant chemistry occurs at the interface between two immiscible liquids, at the liquid/solid interface and at the free liquid (liquid/vapor) interface. Examples are reactions of atmospheric pollutants at the surface of water droplets[6], phase transfer catalysis[7] at the organic liquid/water interface, electrochemical electron and ion transfer reactions at liquidAiquid interfaces[8] and liquid/metal and liquid/semiconductor Interfaces. Interfacial chemical reactions give rise to changes in the concentration of surface species, but so do adsorption and desorption. Thus, understanding the dynamics and thermodynamics of adsorption and desorption is an important subject as well. 

The above techniques have been used in numerous calculations of solute free energy profiles. Wilson and Pohorille [52] and Benjamin[53] have determined the free energy profiles for small ions at the water liquid/vapor interface and compared the results to predictions of continuum electrostatic models. The transfer of small ions to the interface involves a monotonic increase in the free energy which is in qualitative agreement with the continuum model. This behavior is consistent with the increase in the surface tension of water with the increase in the concentration of a very dilute salt solution, and it represents the fact that small ions are repelled from the liquid/vapor interface. On the other hand, calculations of the free energy profile at the water liquid/vapor interface of hydrophobic molecules, such as phenol[54] and pentyl phenol[57] and even molecules such as ethanol [58], show that these molecules are attracted to the surface region and lower the surface tension of water. In addition, the adsorption free energy of solutes at liquid/liquid interfaces[59,60] and at water/metal interfaces[61-64] have been reported. 

AIMD is still a very time-consuming simulation method and has so far mainly been used to study the structure and dynamics of bulk water [14,15], as well as proton transfer [16] and simple Sjv2 reactions in bulk water [17]. AIMD simulations are as yet limited to small system sizes and real simulation times of not more than a few picoseconds. However, some first applications of this technique to interfacial systems of interest to electrochemistry have appeared, such as the water-vapor interface [18] and the structure of the metal-water interface [19]. There is no doubt... 

Stuart s studies of the structure of the liquid-vapor interfaces of metals and alloys can also be related to his previous research. He developed the first theory of transport in dense simple fluids that explicitly recognizes, and accounts for, the different dynamics associated with short-range repulsion and longer-ranged attraction. He has contributed to the theory of the three-molecule distribution function in a liquid and the theory of melting, and he developed the Random Network Model of water and the first consistent... 

As will be emphasized, some interfaces do not induce vicinal water, such as the water/air and water/saturated water vapor interfaces. Furthermore, it is beyond the scope of this chapter to discuss the structural aspects of water/immiscible liquid interfaces or water/pure metal interfaces (free of any oxides). 

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