Single crystals fold plane

Figure 1. Solid lines - cyclic voltammetric curves for hydrogen and oxygen adsorption at the three Pt single crystal planes investigated determined from the pure (CO free) 0.1 M HC10, solution. Dotted lines - cyclic voltammetric curves of adsorbed CO oxidation (note the sensitivity for the CO oxidation curves has been ten fold attenuated. Sweep rate 50 mv/s.

As a model of the nucleus in polymer crystallisation one often takes a rectangular prism. A breakthrough in this respect was the discovery and exploration of polymer single crystals (Schlesinger (1953) and Keller (1957)) which are indeed small prisms, platelets of polymeric chains, folded back and forth in a direction perpendicular to the basal plane (see Fig. 19.1)... 

The last topic to comment is the difference between the optimum compositions in Ru of the Pt-Ru alloys for the oxidation of CO (50 at.% Ru) and methanol (10-20 at.% Ru). Gasteiger et al. " proposed an explanation based on a statistical modelization of the surface of an alloy containing x at.% Ru. The stmctural atomic model proposed by these authors needs a maximum number of 3-fold platinum sites for the adsorption of the CH3OH molecule, and adjacent to 1 Ru atom to adsorb the OH species. This would correspond to a surface with 8-14 at.% Ru depending on the orientation of the low index single crystal planes, 8% for (111), 10% for (100)... 

CoO(lll) and MnO(lll) polished single crystals of purity 99.9% were provided by Crystal GmBH (Berlin, Germany). The samples were cut and aligned to better than 0.1° prior polishing. After polishing, samples with a surface mosaic spread of about 0.8° for CoO and 1.6° for MnO were obtained. A triangular unit cell was chosen to describe the 3-fold symmetry of the (111) surface plane. The unit vectors are related to the cubic ones by as=[il0]/2, bs=[ll0]/2, Cs=[lll]. The h and k indexes describe the in-plane momentum... 

Figure 8. a) Schematic view of the surface structure of an ideal RuOid 10) singlecrystal, where solid circles represent Ru atoms in the surface plane, open circles O atoms in the surface plane, and dotted open circles O atoms below surface plane b) model of an ideal RuO2(110) single-crystal. Ihe RuO2(110) surface contains two kinds of coordinatively unsaturated (CUS) atoms two-fold bridging O (Obr) and five-fold Ru (Rucus)- The Ojf is the O atoms that lay in the plane in the Ru atoms and posses its bulk-like three-fold coordination. 

Fig. 10.8 Thin-layer electrochemical cell used in SNIFTIR studies and reflection optics (a) Teflon cap (b) N2 inlet (c) glass tube (d) Teflon cell body (e) port for reference electrode (f) ceramic tube (g) Pt wire counter electrode (h) single crystal working electrode (i) hemispherical ZnSe window (k) focal plane for reflection optics (m) instrument focal plane and (n) folding mirrors (From reference 16, with permission.)...

---