Reactions with Metal Surfaces

Gas-surface interactions and reactions on surfaces play a crucial role in many technologically important areas such as corrosion, adhesion, synthesis of new materials, electrochemistry and heterogeneous catalysis. This chapter aims to describe the interaction of gases with metal surfaces in terms of chemical bonding. Molecular orbital and band structure theory are the basic tools for this. We limit ourselves to metals. 

Metal and polysilicon films are formed by a chemical-vapor deposition process using organometallic gases that react at the surface of the IC structure. Various metal silicide films may also be deposited in this manner by reaction with the surface of the silicon wafer to form metal silicides. Glass and pol3uner films are deposited or spin cast or both, as are photoresist films (those of a photosensitive material). This process is accomplished by applying a liquid polymer onto a rapidly rotating wafer. The exact method used varies from manufacturer to manufacturer and usually remains proprietary. 

Secondary Ion Mass Spectroscopic Studies of Adsorption and Reaction at Metal Surfaces Correlations with Other Surface-Sensitive Techniques... 

Fig. 3. Vibrational population distributions of N2 formed in associative desorption of N-atoms from ruthenium, (a) Predictions of a classical trajectory based theory adhering to the Born-Oppenheimer approximation, (b) Predictions of a molecular dynamics with electron friction theory taking into account interactions of the reacting molecule with the electron bath, (c) Born—Oppenheimer potential energy surface, (d) Experimentally-observed distribution. The qualitative failure of the electronically adiabatic approach provides some of the best available evidence that chemical reactions at metal surfaces are subject to strong electronically nonadiabatic influences. (See Refs. 44 and 45.)...

Fig. 4. Accumulating evidence is starting to show that molecules which undergo large amplitude vibration can interact strongly with metallic electrons in collisions and reactions at metal surfaces. This suggests that the Born-Oppenheimer approximation may be suspect near transition states of reactions at metal surfaces.

Corrosion inhibition is primarily associated with acidizing. Buffered hydrofluoric acid compositions have been shown to be less corrosive (147). Corrosion inhibitors are designed to reduce the rate of reaction of fluid with metal surfaces, generally by forming films on the surfaces. Acetylenic alcohols and amines are frequently components of corrosion inhibitor blends. Other compounds that have been used include nitrogen heterocyclics, substituted thioureas, thiophenols, and alpha-aminoalkyl thioethers (148). 

The reaction of organometallics with metal surfaces is a very promising aspect of surface organometallic chemistry related to fine chemicals. The precise understanding of the reactions between organometallics and metal surfaces is essential to obtain highly selective catalysts by this route.292,293... 

In the two previous sections, evidence has been presented concerning the chemisorbed states formed when benzene interacts with metal surfaces. It is not the intention in this Section to discuss benzene hydrogenation in detail, but rather to enquire whether studies of this hydrogen-addition reaction provide information about the chemisorbed state of benzene. 

In addition to stabilizing organic products by reaction with metal-exchanged clays, as indicated above, aluminosilicate minerals may enable the preparation of metal organic complexes that cannot be formed in solution. Thus a complex of Cu(II) with rubeanic acid (dithiooxamide) could be prepared by soaking Cu montmorillonite in an acetone solution of rubeanic acid (93). The intercalated complex was monomeric, aligned with Its molecular plane parallel to the interlamellar surfaces, and had a metal ligand ratio of 1 2 despite the tetradentate nature of the rubeanic acid. 

The Doctor test measures the amount of sulfur available to react with metallic surfaces at the temperature of the test. The rates of reaction depend on metal type, temperature, and time. In the test, a sample is treated with copper powder at 149°C or 300°F. The copper powder is filtered from the mixture. Active sulfur is calculated from the difference between the sulfur contents of the sample (ASTM D129) before and after treatment with copper. 

Reaction of gas-phase molecules with metal surfaces modified... 

In section 3.1, reactions of diatomic molecules with metal surfaces are discussed. These studies, although perhaps not sufficiently complicated to directly address processes of technological interest, have produced considerable insight into the dynamics of gas-surface reactions. Simulations of metal surfaces where more i istic interactions are required than are used in the gas-surface studies are presented in section 3.2. This is followed in section 3.3 by a discussion of simulations of reactions on the surfaces of covalently bonded solids. These final studies are particularly suited for addressing technologically relevant processes due to the importance of semiconductor technology. 

Exchange reactions of H + H2(or Hj) have provided the testing ground for theoretical methods which are used to understand gas-phase chemical dynamics . Interest in modeling the reaction of hydrogen with metal surfaces is therefore not unexpected. In addition, hydrogen often plays an important role in reactions associated with catalysis, so studies of this type also have practical application. 

A.T. Turner, Influence of ultrasound on reactions with metals. Advances in Sonochemistry, T.J. Mason (ed.), JAI Press, London, 1990, 1, 81-118 (h) K.S. Suslick and D. Docktycz, Effects of ultrasound on surfaces and solids, ibid 187-230. 

Several other explanations have been put advanced to explain retention hysteresis, including (1) surface precipitation of metallic cations whose hydroxides, phosphates, or carbonates are sparingly soluble (2) chemical reactions with solid surfaces, including organic surfaces, which form complexes with metallic cations and (3) incorporation into the subsurface organic matter through chemical reactions and biochemical transformation. For the case described by Fig. 5.9 or explanations (1) and (2), the contaminant release always exhibits a hysteresis... 

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