Close-packed metal surfaces

Accordingly, Neurock and co-workers have developed models for the electrochemical interface that retain this concept of hexagonal stmcture over close-packed metal surfaces [FiUiol and Neurock, 2006 Taylor et al., 2006c]. With the use of a screening charge as described in Section 4.3, the sensitivity of the stmctural parameters of water with respect to the electrochemical environment were explored [Taylor et al., 2006a]. The predominant effect stems from the polar nature of the water molecule, in which the water molecules are observed to rotate as a function of the applied potential. 

Fig. 5.5. Geometrical structure of a close-packed metal surface. Left, the second-layer atoms (circles) and third-layer atoms (small dots) have little influence on the surface charge density, which is dominated by the top-layer atoms (large dots). The top layer exhibits sixfold symmetry, which is invariant with respect to the plane group p6mm (that is, point group Q, together with the translational symmetry.). Right, the corresponding surface Brillouin zone. The lowest nontrivial Fourier components of the LDOS arise from Bloch functions near the T and K points. (The symbols for plane groups are explained in Appendix E.)...

Fig. 6.9. Corrugation amplitudes of a hexagonal close-packed surface. Solid curve, theoretical corrugation amplitude for an s and a d,- tip state, on a close-packed metal surface with a=2.88 A and 4>=3.5 eV. The orbitals on each metal atom on the sample is assumed to be 1 i-type. Measured STM corrugation amplitudes are from the data of Wintterlin et al. (1989). The first-principle calculation of Al(lll) is taken from Mednick and Kleinman (1980). The corrugation amplitude for a 4-wave tip state is more than one order of magnitude smaller then the experimental corrugation. (Reproduced from Chen, 1991, with permission.)...

Bemdt, R., Gimzewski, J. K., and Schlittler, R. R. (1992). Tunneling characteristics at atomic resolution on close-packed metal surfaces. Ultramicroscopy, 42-44, 528-532. 

Wintterlin, J., Wiechers, J., Brune, H., Giitsch, T., Hofer, H., and Behm, R. J. (1989). Atomic-resolution imaging of close-packed metal surfaces by scanning tunneling microscopy. Phys. Rev. Lett. 62, 59-62. 

DFT calculations of the structure of the molecularly adsorbed NO are in reasonable agreement with experiments, but overestimate the binding energy [197,198]. A barrier of 2.1 eV to dissociation is predicted by DFT, with the NO at the transition state nearly parallel to the surface and N and atoms in bridge sites [199]. This transition state geometry is similar to that of NO dissociation on other close-packed metal surfaces [200]. There is no global DFT PES so that all theoretical dynamics is based only on empirical model PES. 

Fig. 2. The effect of chemical interactions in STM scans on three close-packed metal surfaces (a) Au(lll), (b) Cu(lll), (c) Al(lll). The left frames show a constant current contour without corrections due to chemical interactions, current and corrugation values, while the right frames show constant current contours with the corrections.

The last example we would like to discuss is a lattice of holes formed in stoichiometric hexagonal (h) BN double layers on Rh(lll), see Fig. 5(c) and [99]. The lattice is composed of holes in the BN-bilayer with a diameter of 24 2 A, and an average distance of 32 2 A. The holes in the upper layer are offset with respect to the smaller holes in the lower layer. We note that well-ordered superstructures with a large period have already been observed some time ago by means of LEED for borazine adsorption onto Re(0001) [102], while borazine adsorption onto other close-packed metal surfaces, such as Pt(lll), Pd(lll), and Ni(lll), leads to the self-limiting growth of commensurate ABN monolayers [103,104]. For BN/Rh(lll) it is not clear at present whether the Rh(lll) substrate is exposed at the bottom of the holes. If this was the case the surface would not only be periodic in morphology but also in chemistry, and therefore would constitute a very useful template for the growth of ordered superlattices of metals, semiconductors, and molecules. 

Table I lists the experimental values of QA for major adatoms such as H, O, N, and C on some close-packed metal surfaces (30-43). Typically, the heat of atomic chemisorption QA decreases while going from the left to right along a transition series and from the top to bottom of a column. This decrease AQA is the least pronounced for monovalent H when, within the series Pt-Ni-W, AQH does not exceed 7 kcal/mol [QH = 61, 63, and 68 kcal/mol for Pt(lll), Ni(lll), and W(110), respectively]. For divalent O and trivalent N, however, the changes in QA from Pt to Ni to W become very large, up to AQA = 40 kcal/mol i.e., Qq = 85-125 kcal/mol and (gN = 115-155 kcal/mol. For tetravalent C, the experimental measurements have been reported only for Ni(lll) and Ni(100), giving Qc = 171 kcal/ mol (43). So, for other metal surfaces we are to use extrapolated estimates of Qc. For C, we assume a somewhat larger spread in QA compared with O and N that is, A<2C = 50 kcal/mol, from Qc = 150 kcal/mol for Pt(l 11)...

The deposition of ceria nanoparticles and films has been studied on close-packed metal surfaces of Ni, Rh, Pd, ... 

S.A., and Woll, C. (1997) Surface phonon dispersion curves for a hexagonally close packed metal surface Ru(OOl). Surf. Sci., 372, 132. 

FIGURE 11.9 Scaling relations between adsorption energies of OH and OOH versus the O adsorption energy, (a) data for close-packed metal surfaces. Results where the solvation by HjO is included are compared to results with no solvation, (b) and (c) data of transition metal oxide surfaces. Adapted from Karlberg and Wahnstrbm (2005) and Rossmeisl et al. (2007). 

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