Surface INDEX

Figure Bl.21.1 shows a number of other clean umeconstnicted low-Miller-index surfaces. Most surfaces studied in surface science have low Miller indices, like (111), (110) and (100). These planes correspond to relatively close-packed surfaces that are atomically rather smooth. With fee materials, the (111) surface is the densest and smoothest, followed by the (100) surface the (110) surface is somewhat more open , in the sense that an additional atom with the same or smaller diameter can bond directly to an atom in the second substrate layer. For the hexagonal close-packed (licp) materials, the (0001) surface is very similar to the fee (111) surface the difference only occurs deeper into the surface, namely in the fashion of stacking of the hexagonal close-packed monolayers onto each other (ABABAB.. . versus ABCABC.. ., in the convenient layerstacking notation). The hep (1010) surface resembles the fee (110) surface to some extent, in that it also...

A superlattice can be caused by adsorbates adopting a different periodicity than the substrate surface, or also by a reconstmction of the clean surface. In figure B 1.21.3 several superlattices that are conmionly detected on low-Miller-index surfaces are shown with their Wood notation. 

A famous, yet simple example Is CO. CO tends to adsorb In highly symmetric positions on low Index surfaces, so that the point groups are C. and C. . The totally symmetric vibrations then... 

Figure 5.11 (T, a, A< ) phase diagrams for all low index surfaces of a-Pt02 (a) and P-PVO2...

The existence of active sites on surfaces has long been postulated, but confidence in the geometric models of kink and step sites has only been attained in recent years by work on high index surfaces. However, even a lattice structure that is unreconstructed will show a number of random defects, such as vacancies and isolated adatoms, purely as a result of statistical considerations. What has been revealed by the modern techniques described in chapter 2 is the extraordinary mobility of surfaces, particularly at the liquid-solid interface. If the metal atoms can be stabilised by coordination, very remarkable atom mobilities across the terraces are found, with reconstruction on Au(100), for example, taking only minutes to complete at room temperature in chloride-containing electrolytes. It is now clear that the... 

Figure 1.5 The surface structures of (i) several high-Miller index stepped surfaces with different terrace widths and step orientations (ii) several high Miller-index surfaces with differing kink concentrations in the steps. From G.A. Somorjai, Chemistry in Two Dimensions, Cornell University Press. London, 1981, pp. 160and 161. Used by permission ofCornell University Press.

Carbon deposition from CO on a cobalt catalyst at low pressures is known to be a structure-sensitive process. CO is adsorbed molecularly on the low index surfaces (Co (0001)), but its dissociation occurs on the Co (1012), Co (1120), and polycrystalline surfaces.5762 Deposition of carbon on Co (1012) and the probable formation of Co3C have been established by Auger emission spectroscopy (AES) and low-energy electron diffraction (LEED) techniques.66... 

Teraoka, I. Arnold, S., Enhancing the sensitivity of a whispering gallery mode microsphere sensor by a high refractive index surface layer, J. Opt. Soc. Am. B 2006, 23, 1434 1441... 

Figure A.l Construction of the most densely packed surfaces of fee and bcc metals, and the outer atomic layer of the low-index surfaces. The hep (001) surface has the same structure as...

We can create surfaces from the fee, hep and bcc crystals by cutting them along a plane. There are many ways to do this Fig. A. 1 shows how one obtains the low-index surfaces. Depending on the orientation of the cutting plane we obtain atomically flat surfaces with a high density of atoms per unit area or more open surfaces with steps, terraces and kinks (often referred to as corrugated or vicinal surfaces). Thus, the surface of a metal does not exist one must specify its coordinates. 

The underpotentlal deposition of lead has been examined on LEED-characterized single crystal silver surfaces with 0.1 M HF as the electrolyte using a special ultra-high vacuum-electrolyte transfer system. Each of the low index surfaces has a characteristic voltammetry curve with multiple adsorption and desorption UPD peaks. 

Hydrogen Adsorption on the Low-Index Surfaces. The data on the hydrogen electrosorption on the low-index planes of Pt differ in some detail, as will be discussed below with the help of results for stepped surfaces. 

Voltammetry curves for all three low-index surfaces are given in Fig. 1. Hydrogen adsorption at Pt(lll), the process at -0.25 < E < -0.05 V in Fig. 1, is not affected by the nature of the anion (such as SO 2-, CIO.- or F-) (12). The lack of a well defined peak, in the drawn-out curve of Fig. 1 clearly indicates a strong lateral repulsion between adsorbed hydrogen adatoms. This is probably a consequence of a partially charge on the adsorbed hydrogen adatoms which, in turn, does not allow the... 

Identification of Peaks for Hydrogen Adsorption on the Disordered Low Index Planes. Besides the major objective for studying electrocatalysis on single crystal stepped surfaces mentioned above, these studies offer a wealth of information on the behaviour of polycrystalline surfaces, of preferentially oriented surfaces and, as we suggested recently (12), of disordered low-index surface. 

The shape of the single crystal obtained by the method described above is a sphere with several flat facets as drawn in Fig. 2-6. Usually seven large facets, which are assigned to seven of possible eight (111) surfaces, are seen on the apex positions of a cube. Five small facets, which are assigned to five of possible six (100) surfaces, are also seen on the center of the faces of a cube. The missing (111) and (100) facets are supposed to be located where the shaft is attached. Figure 2—7 shows the relative positions of the three low index surfaces of platinum, which is a face-centered cubic lattice. 

To obtain the three low index surfaces, a polishing jig shown in Fig. 2-8 was made. The jig should be such that the inner shaft should move smoothly in the vertical direction but shoiild not rattle in the shell. It is also required that the guide surface be perpendicular to the direction of the shaft motion. The single crystal was attached on the inner shaft by epoxy resin for orientating and polishing. To obtain either the (111) or (100) surface, the orientation of one of the facets was adjusted to be identical with the guide... 

Fig. 2-7 Three low index surfaces of Pt (face centered cubic lattice) si e crystal and their surface atom arrangement and atomic density.

The obtained low index surfaces were examined by Laue back reflection X-ray diffraction photograph method. Figures 2—10 show the obtained photographs. They represent a typical diffraction pattern for each surface and show that the quality of the each surface is high. The areas of the low index surfaces are 0.028, 0.024 and 0.025 cm for Ptdll), (110) and (100), respectively. 

Figs. 2-iO Laue surface X-ray diffraction photographs for three low index surfaces of Pt single crystals. (C) PtdOO)... 

The same group used EMLRS technique to single crystal studies. - Although COad detected on all three low index surfaces. HCOad ss foxmd only on Ptdll) and Pt(lOO) as active intermediates. 

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