Restructuring of surfaces, adsorbate-induced

Tabulations of some surface structures may be found in a review by Van Hove and coworkers (Van Hove et al., 1989) and the reviews by Watson that compare the results of surface structure determinations utilizing different crystallographic techniques (Watson, 1990, 1992). Van Hove has also published a recent review of crystal surface structure, without the tabular presentation of the structural data (Van Hove, 1992). Van Hove and Somorjai have reviewed surface structure from the point-of-view of adsorbate induced restructuring of surfaces (Van Hove and Somorjai, 1989). Ohtani and coworkers have listed all observed overlayer structures and surface symmetries, albeit without any reference to the detailed surface structure (Ohtani et al., 1987). 

Adsorbate-induced restructuring of surfaces could explain the formation of cluster-like bonding of adsorbates on metal surfaces. Discuss how the strength of the chemisorption bond is likely to influence the restructuring of metal surfaces. 

Adsorbate Induced Restructuring. Perhaps, the most striking observation of recent years is the adsorbate induced restructuring of surfaces. This can be demonstrated by the restructuring of the nickel (100) face(13) in the presence of half a monolayer of carbon... 

K. Kern, H. Niehus, A. Schatz, P. Zeppenfeld, J. George, G. Comsa, Long-range spatial selforganization in the adsorbate-induced restructuring of surfaces—Cu(110)-(2 x 1)0. Phys. Rev. Lett. 67(7), 855-858 (1991)... 

An extreme case of chemisorption-induced restructuring of metal surfaces is coirosive chemisorption as observed by SFG. In this circumstance, metal atoms break away from step or kink surface sites and form bonds with several adsorbate molecules. Carbon monoxide can form several carbonyl ligand bonds with platinum atoms leading to the creation of metal-carbonyl species. Thus, metal-metal bonds are broken in favor of forming metal-carbonyl clusters that are more stable at high CO pressures. The SFG vibrational spectra detect the reversible formation of new adsorb carbon monoxide species above 1(X) Torr on Pt(l 11), that appear to be platinum-carbonyl clusters Pt (CO) , with (m/n) > 1 and a CO commensurate overlayer. 

Defect sites (steps or kinks) and rough, low-packing-density surfaces have higher charge densities near the Fermi level. This is shown by lower work functions and the higher densities of filled electronic states detected by photoemission studies. These rough surfaces restructure more readily when clean, as described in Chapter 2. They are likely to participate in more massive adsorbate-induced restructuring... 

The work of adhesion is also related to the force needed to break chemical bonds at the interface on the atomic scale. When bonds form at the interface of two solids, restructuring can occur at both sides of the interface, thereby optimizing the strength of the interfacial chemical bond. This restructuring is related to the adsorbate-induced restructuring processes and to the phenomenon of epitaxy that was discussed in Chapters 2 and 5. It involves the movement of atoms perpendicular, as well as parallel, to the interface. We may call this movement the work of interface restructuring It involves surface atoms as well as atoms two to three layers away from... 

Oscillations connected with adsorbate-induced surface restructuring were studied also in [29]. The model used was aimed at mimicking oscillations in NO reduction by H2 on a mesoscopic Pt particle containing two catalytically active (100) areas connected by an inactive (111) area that only adsorbed NO reversibly. NO diffusion on and between facets was much faster than other steps. The results obtained show that the coupling of the catalytically active sublattices may synchronize nearly harmonic oscillations observed on these sublattices and also may result in the appearance of aperiodic partially synchronized oscillations. The spatiotemporal patterns corresponding to these regimes are nontrivial. In particular, the model predicts that, due to phase separation, the reaction may be accompanied by the formation of narrow NO-covered zones on the (100) sublattices near the (lOO)-(lll) boundaries. These zones partly prevent NO supply from the (111) sublattice to the (100) sublattices. 

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