Monoatomic step

Figure Al.7.1. Schematic diagram illustrating terraces, steps, and defects, (a) Perfect flat terraces separated by a straight, monoatomic step, (b) A surface containing various defects.

Figure 6.35. Potential energy diagrams for adsorption and dissociation of N2on a Ru(0001) surface and on the same surface with a monoatomic step, as calculated with a density functional theory procedure. [Adapted from S. Dahl, A. Logadottir, R. Egberg, J. Larsen, I. Chorkendorff,...

We would also like to point out some essential differences in site geometry between particle edges and monoatomic steps, which may be crucial for some catalytic... 

Figure 3.1 The first images recorded using a scanning tunnelling microscope to be published. Monoatomic steps are visible at (a) CaIrSn4 and (b) Au(lll) surfaces. (Reproduced from Ref. 43).

The electrocrystallization on an identical metal substrate is the slowest process of this type. Faster processes which are also much more frequent, are connected with ubiquitous defects in the crystal lattice, in particular with the screw dislocations (Fig. 5.25). As a result of the helical structure of the defect, a monoatomic step originates from the point where the new dislocation line intersects the surface of the crystal face. It can be seen in Fig. 5.48 that the wedge-shaped step gradually fills up during electrocrystallization after completion it slowly moves across the crystal face and winds up into a spiral. The resultant progressive spiral cannot disappear from the crystal surface and thus provides a sufficient number of growth... 

Fig. 4.6 STM images from an Ru(0001) surface with a monoatomic step after adsorption of NO at 300 K (a) 6 min after exposure, (b) 120 min after exposure. [21]...

Fig. 4.7 Chemisorption of O atoms near the two types of monoatomic steps on an Ru(0001) surface...

Steps, or growth layers, are structure components for construction of a variety of growth forms in the electrodeposition of metals (e.g., columnar crystals, whiskers, fiber textures). We can distinguish between monoatomic steps, polyatomic microsteps, and polyatomic macrosteps. Only the propagation of polyatomic steps can be observed directly, in situ. 

Microsteps, There is in general a tendency for a large number of thin steps to bunch into a system of a few thick steps. Many monoatomic steps can unite (bunch, coalesce) to form a polyatomic step. Frank (4) proposed a bunching mechanism to explain this process. Bunching of steps is illustrated schematically in Figure 7.12. 

Layer Growth. In Section 7.9 we showed that many monoatomic steps can unite (bunch, coalesce) to form polyatomic steps in the presence of impurities. Additives can also influence the propagation of microsteps and cause bunching and formation of macrosteps. 

The Saddle Point Features of the 2-D Gratings For an ideal 2-D sinewave the saddle point features should appear to have 4-fold symmetry when viewed in LEEM images. From the sketch of figure 13 it can be seen that the hypocycloid shaped terrace at the saddle point has the same type of monoatomic step on all four sides due to the difference in the free energies of the two steps, Sa and Sb, on Si(OOl) there should be a strong preference for Sa steps and hence each maximum would prefer to be flanked by two white domains and two "black ones as is the case in figure 10. (A similar conclusion follows if the the saddle point terrace is surrounded by two Sa steps and two double steps of Db type[31]). 

Figure 8.12 Top Vicinal surface of cubic crystal that has been cut at a small angle relative to the 100 plane exhibiting monoatomic steps. Bottom An additional tilt leads to kinks in the ledges. 

Figure 1 shows the variation of the stationary rate of C02 formation with CO pressure at fixed temperature and 02 pressure for both a well-annealed, flat Pt(l 10) surface (solid line) and the same surface exhibiting periodic arrays of monoatomic steps forming facets (broken line) (23). At low CO pressures, the surface is largely covered by Oad, and the rate increases linearly with pco. Nearly every CO molecule striking the surface... 

Figure 3 Geometry of missing row reconstructed Ag(l 0 0), of Ag(41 0) and of Ag(2 1 0). For the Ag( 1 0) surfaces the scattering plane of both incoming molecules and electrons is aligned along the (I, n, 0) direction (across the monoatomic steps). The surface unit cell and the angles corresponding to normal incidence on the (11 0) and (1 0 0) nanofacets are also drawn.

Figure 11. Model representation of a Au(332) surfaee. Ideally this surface consists of monoatomic steps with (111) step facets and (111) terraces that span 5.5 atomic rows (/= 12 A).

On Si(lll) steps of 3.1 A correspond to the distance between two (111) planes and contain two layers of Si atoms. The terminology monoatomic step is taken here for simplification in the following. 

---