Coincidence Superlattices

Redistribution of the space-charge of the excited carriers is presented in Fig. 1. Therewith at low temperatures, as seen in Fig. 2, the tunable photoluminescence band maximum coincides with the difference of the quasi-Fermi levels AF, which in turn is close to the effective energy gap Eg of the doped superlattice. At... 

Fig. 15 a Schematic drawing of the moir -like coincidence between the Pt(l 11) lattice and the w -TiO t superlattice and b corresponding atomically resolved STM image (from [93])... 

We introdnce the periodic boundary conditions for the crystal domain coinciding with the LUC that is, we assume that all translations through the superlattice vectors A are equivalent to the identity translation. Thus, we have a system of finite size, i.e. a cyclic cluster belonging to the symmetry gronp = T F, see Sect. 2.2.3... 

Fig. 52. The temperature dependence of the Gaussian width of the principal magnetic peak from a Ho2o/Et2o superlattice. For T 7N(Er) the width is constant, and decreases rapidly below this temperature. In the temperature interval marked by a C the position of the magnetic peak coincided with that of a charge peak, so that its width could not be determined. (From Simpson et al. 1996.)...

The value of det C thus characterizes the distortion of the ideal crystal structure due to cleavage. When det C is an integer, the superlattice is referred to as simple (Figs 2.2a, b). When detC is a rational number, the superstructure is called coincidence lattice. In such a case, if there is no angle between the... 

Figure 4.22 Coincidence superlattice of the reconstructed Ir(lOO) surface (for details, see text).

Of course, when there are no equivalent adsorption sites, there is no superceU applying to both the adsorbate and the substrate. Yet, as demonstrated in panel (c) of Figure 4.23, one can choose a large unit cell so that there is an approximate coincidence of adsorption sites equivalent to an approximate coincidence superlattice. Even more, as there will be always some residual influence of the substrate, the species adsorbed may reside at different heights in a way that the unit cell of the adsorbate is that of the mentioned (approximate) coincidence superlattice. Also, an adsorbate atom may lock into a high-coordination site when it comes sufficiently... 

For the (100) surfaces of Pt and Au, the hexagon is almost undisturbed. As a consequence, an incommensurate superstracture results, which, however, has been described frequently by approximate coincidence superlattices as, for instance, (5 X 20). Also, the hexagon has been found to rotate with the rotation angle being a function of temperature (in the range 0.7-0.9° [89, 90]). This is possibly due to... 

Figure 4.34 Quasi-hexagonal reconstruction of the Ir(lOO) surface. The top-layer atoms of the bulk-terminated surface (a) rearrange to sixfold intralayer coordination (b). The resulting hexagon (c) is slightly distorted (quasi-hexagon (d)) so that a (5 x 1) coincidence superlattice results (e). By bonding to the quadratic substrate layer, the surface...

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