Polycrystalline and single crystalline

In non-electrochemical heterogeneous catalysis, the interface between the catalyst and the gas phase can often be characterized using a wide variety of spectroscopic probes. Differences between reaction conditions and the UHV conditions used in many studies have been probed extensively 8 as have differences between polycrystalline and single-crystalline materials. Nevertheless, the adsorbate-substrate interactions can often be characterized in the absence of pressure effects. Therefore, UHY based surface science techniques are able to elucidate the surface structures and energetics of the heterogeneous catalysis of gas phase molecules. 

Consider the diffusivity data presented in Figure 4.42 for the self-diffusion of silver in polycrystalline and single-crystalline form. Use the correlations provided to calculate the following quantities. 

The answer to the above is a clear and emphatic yes as first shown by ourselves on the (111) and (100) single crystal surfaces of NiSi2 (5) and more recently by Ross and coworkers on both polycrystalline and single crystalline Pt3Ti (12.13). We note that, although most studies to date have dealt with zero-valent materials, partially oxidized species may show similar effects. In the case of metal crystallites supported on reducible oxide substrates (14), these latter materials may, in fact, be more relevant. Despite this, the properties of zero valent intermetallic surfaces can provide useful insights as we shall show below. 

Lattice thermal conductivity data below 300 K for representative clathrates are summarized in Fig. 6.4 [35, 40 4], These data, for a representative number of compositions collected from both polycrystalline and single crystalline specimens, allow for a comparison of the effect of guest and framework composition on Kl. While some compositions have lattice thermal conductivities that are characteristic of glasses, others have Kl values that more closely resemble the typical temperature dependence of defect-free crystalline solids in which Umklapp processes [24] produce a monotonically decreasing Kl with increasing temperature above 10 K. 

Bulk CO Oxidation on Polycrystalline and Single Crystalline Pt Electrodes... 

Amorphous, microcrystalline, polycrystalline, and single-crystalline silicon are important building blocks in the construction of miniature silicon architectures by microlithography. Each silicon crystallinity has a slightly different characteristic Raman shift associated with the silicon first-phonon band. LCTF Raman chemical imaging can be applied to measure the distribution of silicon crystallinities within an integrated-circuit test pattern. The test pattern contains single-crystal silicon with a thin oxide layer and polycrystalline silicon epitaxially deposited on the monocrystalline silicon substrate. 

Westerholt etal. [32] compared magnetic transition temperatures as a function of lattice constant in polycrystalline and single crystalline EuSe under hydrostatic pressure (p = 0 to... 

Superhard Abrasives Quartz sand, garnet, and corundum have been used as abrasives for many centuries. Another abrasive that has been used is natural diamond. Various superhard abrasives have been synthesized during the twentieth century. They are SiC, B4C, TiC, cubic BN, polycrystalline, and single-crystalline diamond. 

Nanocarbon hybrids have recently been introduced as a new class of multifunctional composite materials [18]. In these hybrids, the nanocarbon is coated by a polymer or by the inorganic material in the form of a thin amorphous, polycrystalline or single-crystalline film. The close proximity and similar size domain/volume fraction of the two phases within a nanocarbon hybrid introduce the interface as a powerful new parameter. Interfacial processes such as charge and energy transfer create synergistic effects that improve the properties of the individual components and even create new properties [19]. We recently developed a simple dry wrapping method to fabricate a special class of nanocarbon hybrid, W03 /carbon nanotube (CNT) coaxial cable structure (Fig. 17.2), in which W03 layers act as an electrochromic component while aligned... 

Figure 10. Polarizing micrograph of a dewetted sample of 185 on a glass substrate. Overview of the pattern (left). Polycrystalline dome prepared by annealing at room temperature (top right) and single crystalline domes prepared by annealing at 50 C (bottom right).

Chronoamperometric transients for CO stripping on polycrystalline platinum were measured by McCallum and Fletcher [1977], Love and Lipkowski [1988] were the hrst to present chronoamperometric data for CO stripping on single-crystalline platinum. However, they interpreted their data on the basis of a different model than the one discussed above. Love and Lipkowski considered that the oxidation of the CO adlayer starts at holes or defects in the CO adlayer, where OH adsorbs. These holes act as nucleation centers for the oxidation reaction, and the holes grow as the CO at the perimeter of these holes is oxidized away by OHads- This nucleation and growth (N G) mechanism is fundamentally different from the mean held model presented above, because it does not presume any kind of mixing of CO and OH [Koper et ah, 1998]. Basically, it assumes complete surface immobility of the chemisorbed CO. 

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