Added rows

Fig. 34.25. Time windows in which compounds are present in a composite 4-component peak, with the ranks of the data matrices formed by adding rows to a top matrix To (top down) or to a bottom matrix B(, (bottom up).

Fig. 34.26. Eigenvalues when adding rows to To (forward evolving PCA).

The first STM evidence for the facile transport of metal atoms during chemisorption was for oxygen chemisorption at a Cu(110) surface at room temperature 10 the conventional Langmuir model is that the surface substrate atoms are immobile. The reconstruction involved the removal of copper atoms from steps [eqn (1)], resulting in an added row structure and the development of a (2 x 1)0 overlayer [eqn (2)]. The steps present at the Cu(llO) surface are... 

Chemisorption of oxygen at Ag(110) at 300 K forms added rows of-Ag-O-extending along the [001] direction much like those observed with Cu(110). At saturation the monolayer, as with Cu(110), has a (2 x 1)0 structure.16 On exposure to ammonia at 300 K, Guo and Madix established17 that this oxide structure undergoes extensive restructuring where the added silver atoms in the monolayer are released to form nanoscale islands with the formation of... 

At an Ni(110)-O surface exhibiting a (3 x 1) structure (0.3 ML of oxygen), benzene adsorption at room temperature induces a compression of the (3 x 1) added-row to a (2 x 1) structure. There was no evidence for a direct reaction between the surface oxygen and benzene, but on heating to 600 K the oxygen is removed (as CO) and the surface is clean, other than areas of a p(4 x 5)C carbidic phase.41... 

Of crucial significance in deciding between various models have been estimates of the number of copper atoms required to transform the surface into a (2 x 3)N phase. This was the approach adopted by Takehiro et al 2 in their study of NO dissociation at Cu(110). They concluded that by determining the stoichiometry of the (2 x 3)N phase that there is good evidence for a pseudo-(100) model, where a Cu(ll0) row penetrates into the surface layer per three [ll0]Cu surface rows. It is the formation of the five-coordinated N atoms that drives the reconstruction. The authors are of the view that their observations are inconsistent with the added-row model. The structure of the (2 x 3)N phase produced by implantation of nitrogen atoms appears to be identical with that formed by the dissociative chemisorption of nitric oxide. 

There are no rows with all zero elements in the reduced matrix of Fig. 9a, hence we proceed to the second phase of Steward s algorithm by starting with the first row of the reduced matrix to trace the path 2 - 3 -> 4 -> 2. The loop of information flow between vertices 2, 3, and 4 is encircled by the dashed line in the graph in Fig. 9b. The rows and columns labeled 2, 5, and 4 are next removed from the reduced matrix and one row, which is the Boolean union of the rows labeled 2, 3, and 4, and one column, which is the Boolean union of the columns labeled 2, 2, and 4, are added to the reduced matrix to obtain the new reduced matrix of Fig. 10a. The added row and column are labeled... 

Quantitative determination of the local adsorption structure of carbonate on Ag(llO) has been done by Kittel etal. [110]. They have found that the carbonate species is essentially planar and adsorbs almost parallel to the surface at the off-atop site with respect to the outermost layer Ag atom. The C—Ag layer spacing was 0.264 0.009 nm, with a well-defined azimuthal orientation. This geometry is understood best in terms of the added-row model proposed by Guo and Madix. This model assumes that additional Ag atoms lie adjacent to the carbonate, such that the... 

Recent experiments on the coverage dependence of the sticking of 02 to Ag(l 1 0) revealed a remarkable drop shown in Fig. 20 [172-179]. This drop has been explained by electrostatic effects [179]. Butler et al. have attributed the drop to the build-up of added rows at the surface [180], If the picture of adsorption into a metastable intermediate is valid, it implies that the intermediate should be stabilized at a step edge. Subsequently the molecule can dissociate at the site and form an Ag-O pair, that is inserted into an added row. This involves mass transport at the surface, which has been observed in... 

Figure 21 Schematic drawing of the random-walk diffusion model of Butler et al. [180]. It is shown that molecular intermediates that do not hit an added row may dissociate at a step, bind to an Ag-atom and insert in an added row.

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