Metal surfaces, theory

Diffusion of vacancies in metal surfaces theory and experiment... 

L. Falicov and G.A. Somoijai. Correlation between Catalytic Activity and Bonding and Coordination Number of Atoms and Molecules on Transition Metal Surfaces Theory and Experimental Evidence. Proc. Natl. Acad. Sci. USA S2i2207 (1985). 

Levitin, V. and Loskutov, S. (2009) Strained Metallic Surfaces Theory, Nanostructuring and Fatigue Strength, Wiley-VCH Verlag GmbH, Weinheim. 

Whitten J L and Pakkanen T A 1980 Chemisorption theory for metallic surfaces Electron localization and the description of surface interactions Phys. Rev. B 21 4357-67... 

Whitten J L and Yang H 1996 Theory of chemisorption and reactions on metal surfaces Surf. Sc/. Rep. 24 59-124... 

Baer R and Kosloff R 1997 Quantum dissipative dynamics of adsorbates near metal surfaces a surrogate Hamiltonian theory applied to hydrogen on nickel J. Chem. Rhys. 106 8862... 

A type of molecular resonance scattering can also occur from the formation of short-lived negative ions due to electron capture by molecules on surfrices. While this is frequently observed for molecules in the gas phase, it is not so important for chemisorbed molecules on metal surfaces because of extremely rapid quenching (electron transfer to the substrate) of the negative ion. Observations have been made for this scattering mechanism in several chemisorbed systems and in phys-isorbed layers, with the effects usually observed as smaU deviations of the cross section for inelastic scattering from that predicted from dipole scattering theory. 

Because LEED theory was initially developed for close packed clean metal surfaces, these are the most reliably determined surface structures, often leading to 7 p factors below 0.1, which is of the order of the agreement between two experimental sets of 7-V curves. In these circumstances the error bars for the atomic coordinates are as small as 0.01 A, when the total energy range of 7-V curves is large enough (>1500 eV). A good overview of state-of-the-art LEED determinations of the structures of clean metal surfaces, and further references, can be found in two recent articles by Heinz et al. [2.272, 2.273]. 

J. Mai, W. von Niessen. The CO -(- O2 reaction on metal surfaces. Simulation and mean-field theory The influence of diffusion. J Chem Phys 95 3685-3692, 1990. 

The results obtained demonstrate competition between the entropy favouring binding at bumps and the potential most likely to favour binding at dips of the surface. For a range of pairwise-additive, power-law interactions, it was found that the effect of the potential dominates, but in the (non-additive) limit of a surface of much higher dielectric constant than in solution the entropy effects win. Thus, the preferential binding of the polymer to the protuberances of a metallic surface was predicted [22]. Besides, this theory indirectly assumes the occupation of bumps by the weakly attracted neutral macromolecules capable of covalent interaction with surface functions. 

The accuracy of LDF calculations in the prediction of surface geometries not only holds for clean metal surfaces such as the W(001) surface discussed above, but is also found for adsorbates such as H (27), O (28), and S (29) on Ni(OOl) surfaces. Rather than going into detail on clean and adsorbate covered surfaces, we will now focus on the description of the C-C bond by LDF theory. To this end, we first discuss a layer of condensed benzene rings, i.e. a graphite monolayer, and then focus our attention on the ethylene molecule. 

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. 

J. F. Cornwell, Group Theory in Physics. Vol. 1, Academic Press, London (1989). See e.g. Electrons in Disordered Metals and at Metallic Surfaces. P. Phariseau,... 

The Gouy-Chapman theory for metal-solution interfaces predicts interfacial capacities which are too high for more concentrated electrolyte solutions. It has therefore been amended by introducing an ion-free layer, the so-called Helmholtz layer, in contract with the metal surface. Although the resulting model has been somewhat discredited [30], it has been transferred to liquid-liquid interfaces [31] by postulating a double layer of solvent molecules into which the ions cannot penetrate (see Fig. 17) this is known as the modified Verwey-Niessen model. Since the interfacial capacity of liquid-liquid interfaces is... 

Numerous quantum mechanic calculations have been carried out to better understand the bonding of nitrogen oxide on transition metal surfaces. For instance, the group of Sautet et al have reported a comparative density-functional theory (DFT) study of the chemisorption and dissociation of NO molecules on the close-packed (111), the more open (100), and the stepped (511) surfaces of palladium and rhodium to estimate both energetics and kinetics of the reaction pathways [75], The structure sensitivity of the adsorption was found to correlate well with catalytic activity, as estimated from the calculated dissociation rate constants at 300 K. The latter were found to agree with numerous experimental observations, with (111) facets rather inactive towards NO dissociation and stepped surfaces far more active, and to follow the sequence Rh(100) > terraces in Rh(511) > steps in Rh(511) > steps in Pd(511) > Rh(lll) > Pd(100) > terraces in Pd (511) > Pd (111). The effect of the steps on activity was found to be clearly favorable on the Pd(511) surface but unfavorable on the Rh(511) surface, perhaps explaining the difference in activity between the two metals. The influence of... 

More recently the application of sub-picosecond, time-resolved pump-probe methods revealed the timescale for vibrational relaxation of a diatomic molecule at a metal surface directly. See for example Refs. 19-21. In comparison to vibrational relaxation on NaCl salts,22 which occurs on the millisecond timescale, another relaxation mechanism is clearly at play. Theory of vibrational relaxation based on excitation of electron-hole pairs gave agreement with observed ps timescales for CO on copper.23... 

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.)...

The above effects are more familiar than direct contributions of the metal s components to the properties of the interface. In this chapter, we are primarily interested in the latter these contribute to M(S). The two quantities M(S) and S(M) (or 8% and S m) are easily distinguished theoretically, as the contributions to the potential difference of polarizable components of the metal and solution phases, but apparently cannot be measured individually without adducing the results of calculations or theoretical arguments. A model for the interface which ignores one of these contributions to A V may, suitably parameterized, account for experimental data, but this does not prove that the neglected contribution is not important in reality. Of course, the tradition has been to neglect the metal s contribution to properties of the interface. Recently, however, it has been possible to use modern theories of the structure of metals and metal surfaces to calculate, or, at least, estimate reliably, xM(S) and 5 (as well as discuss 8 m, which enters some theories of the interface). It is this work, and its implications for our understanding of the electrochemical double layer, that we discuss in this chapter. 

---