Surface low index

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...

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... 

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. 

The discussion on the experimental evidence for the existence of roughening on low indexed surfaces is not yet settled. Let us consider for example the Cu(110) surface. More than ten years ago it had been noticed that the intensities in the photoemission spectra taken from Cu(l 10) decrease rapidly with temperature above 500 K Similar effects have been seen recently in... 

In contrast to the detailed work on the Au(l 11) surface, desorption studies from the other low-index surfaces are scarce with, for example, MC9 and MC4/8 on Au(l 10) [45, 46] and MC4 [47] on Au(l 00). Compared to Au(l 11) thiols are more stable on Au(l 10) as reflected by a negative shift of the desorption peak by 200-300 mV, which was explained by the difference in the pzc for both surfaces [46]. N o obvious differences in the shape of the desorption peaks were found for Au( 1 0 0) compared to Au(l 11). Interestingly, for MC4 a higher thiol coverage compared to both MC4 on the Au(l 11) and MC2 Au(l 0 0) was concluded from the desorption studies. For polycrystalline surfaces the desorption signal is more complicated with additional features, possibly due to the presence of different crystallographic domains [94, 163, 164]. 

Figure 4.7 shows top-down views of the fee (001), (111), and (110) surfaces. These views highlight the different symmetry of each surface. The (001) surface has fourfold symmetry, the (111) surface has threefold symmetry, and the (110) has twofold symmetry. These three fee surfaces are all atomically flat in the sense that on each surface every atom on the surface has the same coordination and the same coordinate relative to the surface normal. Collectively, they are referred to as the low-index surfaces of fee materials. Other crystal structures also have low-index surfaces, but they can have different Miller indices than for the fee structure. For bcc materials, for example, the surface with the highest density of surface atoms is the (110) surface. 

So far we have only shown examples of low-index surfaces. These surfaces are important in the real world because of their stability. They are also quite... 

Tab. 4.3 Calculated energies fo r relaxed, low index surfaces of hematite...

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