Terrace structure

Vitus and Davenport showed that upon anodic oxidation of Au(l 11), a monolayer of AuO was formed on the surface, maintaining the surface crystallinity. Subsequent electrochemical reduction of the oxide formed a characteristic wormlike structure that coarsened in a matter of hours to restore the original terrace structure of the substrate surface. This result shows that repeated potential cycling performed in the anodic region may destroy or roughen the surface owing to a lack of coalescence of surface atoms after oxide reduction. 

Terrace structure on TiO2(110) (1x1) has been observed with atomic or unit cell resolution by many groups in the past few years [167-180]. There is a general consensus that under conditions of positive sample bias the images are dominated by bright rows running along the [001] direction with a separation of... 

Atomic surface order can be adequately described in terms of a simple unit cell, and techniques for the preparation of surfaces with defined atomic order are well established. Describing mesoscopic structures is not as easy. But single crystals do not always consist of only well-defined terrace structure—they also contain steps, and possibly other irregular surface features such as kinks and defects. The mobility... 

In contrast, both vacuum-deposited films on Ti02 with and without template layer showed a well-ordered and terraced structure with a step height of 1.5 0.1 nm (see Figures 5.7 and 5.8). The data were determined with height distri-... 

Figure 5.7 Non-contact AFM images of DCNDBQT without template layer evaporated on Ti02 (a) 5 pm image of the prepared sample, (b) zoomed image showing the terrace structures, (c) high resolution image with a unit cell of a = 2.0 nm, b = 0.1 nm, c = 1.5 nm.

FIG. 23 Schematic illustration of the formation of an SECM-induced dissolution pit with terraced walls. The UME induces dissolution from the area directly under it (a), resulting in a current surge. The flux of material from this area then rapidly declines and slow dissolution occurs from the edge of the resulting pit (b), resulting in expansion. Concurrently, the area directly under the center of the UME becomes increasingly undersaturated, until the critical value for the creation of fresh dissolution sites is attained, when there is a subsequent burst of material from the surface (c), producing a terraced structure within the pit. The overall process may then be repeated. 

Figure 4. Structure of as prepared iron foil. Key a, grain structure after high temperature annealing at 850°C b, typical step structure at a thermal groove and c, terrace structure developed at sites away from grain boundaries.

Fig. 19. Work-function change A4>co after saturated CO adsorption at 300 K. A I>co vs. work function of corresponding clean surface area hkl. Symbols indicate terrace structure. Dashed line represents linear regression line, (a) Platinum. Intercept, Aq = 5.2 0.2 eV slope, Aj=-0.92 0.04 r = 0.997, without 210 and 320. (b) Rhodium. Intercept, Aq = 6.9 0.9 eV slope, Aj= -1.2 0.2 r = 0.97, without 430 and 321. From 90L. ...

Figure 3.4.1.19 Structure of the Si(OOI) sur- these terraces are shown in (d) and (e). The face, (a) Side view of the unreconstructed structures of a vicinal Si(OOI) surface with (ideal) surface near a monoatomic step. The exclusively single-height steps and exclusively terrace structures on either side of the step double-height steps are shown in (f) and (g). are shown in (b) and (c). Reconstructions of respectively. Adapted from Ref. [135].

As the step ions are coordinatively more unsaturated than those on the regular terrace, structural relaxation around the step is to be expected. Some theoretical studies [101-103] have addressed this point and the results are depicted in the inset in Figure 15.23a, showing in gray the atomic positions of the unrelaxed step and in black those after relaxation. The ion displacement amounts to only a small percentage of the interionic distance however, as can be inferred from Figure 15.23, it goes in directions that tend to smooth out the step and make it more round. 

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