Crystallographic surface orientation, effect

The newest trend has been to deposit controlled amounts of ruthenium on the well-defined platinum single-crystal substrates of different crystallographic orientations. This approach allows one to investigate surface-structure effects in PtRu... 

Despite extensive studies that have been conducted on the wettability of ceramics, only few research papers have focused on the effect of crystallographic orientation on the wetting behavior. For the first time, studies have been carried out to clarify the wetting of metals on the Al Oj single crystals with different surface orientations. For example, Shen et al. (Shen et al., 2003) studied the wetting behavior of (0001) a-Al Oj by molten Al at 973-1773 K... 

The experimental studies of the surface properties of monocrystals of oxides of various metals recently conducted at well-controlled conditions [32, 210] enable one to proceed with detailed analysis of separate effects of various factors on characteristics of semiconductor gas sensors. In this direction numerous interesting results have been obtained regarding the fact of various electrophysical characteristics of monocrystalline adsorbents on the value of adsorption-related response. Among these characteristics there are crystallographic orientation of facets [211], availability of structural defects, the disorder in stoichiometry [32], application of metal additives, etc. These results are very useful while manufacturing sensors for specific gases with required characteristics. 

In reality, as the barrier becomes narrower, it deviates from the square shape. One often used model is the parabolic barrier (dashed line in Fig. 1). When the barrier is composed of molecules, not only is the barrier shape difficult to predict, but the effective mass of the electron can deviate significantly from the free-electron mass. In order to take these differences into account, a more sophisticated treatment of the tunneling problem, based on the WKB method, can be used [21, 29-31]. Even if the metals are the same, differences in deposition methods, surface crystallographic orientation, and interaction with the active layer generally result in slightly different work functions on either side of the barrier. 

There is a negligible effect of adsorbate-adsorbate interaction on step surfaces. Some lateral repulsion of hydrogen adsorbed on Pt(lll) could be inferred. A strong adsorption of bisulphate and sulphate anions on the (111) oriented terraces and step sites considerably affects both reactions. These data show that each crystallographic orientation of the electrode surfaces gives a different electrochemical entity. 

We may conclude that on polycrystalline material, where various crystallographic orientations will be present at the surface, a certain degree of heterogeneity will result from the different heats of adsorption on the different crystal faces. As we see, however, from the difference in the work functions of tungsten, these differences are not extremely large. We may perhaps expect that a certain part of the observed decrease of heats of chemisorption with increasing 6 values may be ascribed to this heterogeneity, but it seems doubtful that the whole effect should be caused by it. 

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