Crystalline surface structure

The main aim of these studies is how to enhance the oxidation of glucose therefore, upd studies are also involved. As in the previous cases, the role of the crystalline surface structure of platinum electrodes in the electrooxidation is also studied. A series of studies was carried out by Wilde and Zhang using EQCM technique, in the presence and absence of adatoms in both acid and alkaline media. Unfortunately, owing to the very nature of the technique used, only phenomenological conclusions can be drawn from these latter studies and no information is furnished about the nature of the adsorbed species. The same refers to some other studies. ... 

E. Other techniques Low-energy electron diffraction Elastic low-energy electron diffraction Inelastic low-energy electron diffraction Reflection high-energy electron diffraction LEED ELEED ILEED RHEED 50 A Crystalline surface structure Limited applicability 128, 129, 130... 

Particle size and Major elements Structure (crystalline Surface structure... 

Lang and Clavilier studied the influence of the crystalline surface structure of platinum on the electrochemical polymerization of 3-methylthiophene [63]. The superficial crystalline structure greatly influenced the location of the polymer film on a polyoriented electrode surface. At a low polymerization potential, the (111) facets were first covered with polymer film. The... 

The role of the crystalline surface structure, and in particular long range surface order, of platinum electrodes in the electrooxidation of D-glucose in acidic media has been discussed. Papers have been published on the effects of adsorbed anions on the oxidation of D-glucose on gold single crystal electrodes, and on the oxidation of D-sorbose and 2,3 4,6-di-0-isopropylidene-a-L-sorbose by air over supported platinum and palladium catalysts. ... 

RHEED is a powerful tool for studying the surface structure of crystalline samples in vacuum. Information on the surface symmetry, atomic-row spacing, and evidence of surfece roughness are contained in the RHEED pattern. The appearance of the RHEED pattern can be understood qualitatively using simple kinematic scattering theory. When used in concert with MBE, a great deal of information on film growth can be obtained. 

ReflEXAES can be used for near-surface structural analysis of a wide variety of samples for which no other technique is appropriate. As with EXAES, ReflEXAES is particularly suited for studying the local atomic structure around particular atomic species in non-crystalline environments. It is, however, also widely used for the analysis of nanocrystalline materials and for studying the initial stages of crystallization at surfaces or interfaces. ReflEXAES was first proposed by Barchewitz [4.135], and after several papers in the early nineteen-eighties [4.136, 4.168-4.170] it became an established (although rather exotic) characterization technique. Most synchrotron radiation sources now have beam-lines dedicated to ReflEXAES experiments. 

The singlet-level theory has also been used to describe the structure of associating fluids near crystalline surfaces [30,31,76,77]. The surface consists explicitly of atoms which are arranged on a lattice of a given symmetry. The fluid atom-surface atom potential can also involve an associative term, i.e., the chemical-type bonding of the adsorbate particles with the surface may be included into the model. However, we restrict ourselves to the case of a nonassociative crystalline surface first. 

Besides crystalline order and structure, the chain conformation and segment orientation of polymer molecules in the vicinity of the surface are also expected to be modified due to the specific interaction and boundary condition at the surface between polymers and air (Fig. 1 a). According to detailed computer simulations [127, 128], the chain conformation at the free polymer surface is disturbed over a distance corresponding approximately to the radius of gyration of one chain. The chain segments in the outermost layers are expected to be oriented parallel to the surface and chain ends will be enriched at the surface. Experiments on the chain conformation in this region are not available, but might be feasible with evanescent wave techniques described previously. Surface structure on a micrometer scale is observed with IR-ATR techniques [129],... 

A wide variety of solid materials are used in catalytic processes. Generally, the (surface) structure of metal and supported metal catalysts is relatively simple. For that reason, we will first focus on metal catalysts. Supported metal catalysts are produced in many forms. Often, their preparation involves impregnation or ion exchange, followed by calcination and reduction. Depending on the conditions quite different catalyst systems are produced. When crystalline sizes are not very small, typically > 5 nm, the metal crystals behave like bulk crystals with similar crystal faces. However, in catalysis smaller particles are often used. They are referred to as crystallites , aggregates , or clusters . When the dimensions are not known we will refer to them as particles . In principle, the structure of oxidic catalysts is more complex than that of metal catalysts. The surface often contains different types of active sites a combination of acid and basic sites on one catalyst is quite common. 

In this section, we will investigate the surface structure of the electrode in the potential range before a surface or bulk oxide starts forming, and will restrict ourselves to the adsorption of atomic oxygen only (not OH ) [Jacob and Scheffler, 2007]. Furthermore, in our simulations, we assume a single-crystal Pt(lll) electrode, which will be compared with the experimental CV curve (Fig. 5.9) for poly crystalline Pt. This simplification is motivated by the fact that our interest here is to describe the general behavior of the system only. 

Phospholipids, which are one of the main structural components of the membrane, are present primarily as bilayers, as shown by molecular spectroscopy, electron microscopy and membrane transport studies (see Section 6.4.4). Phospholipid mobility in the membrane is limited. Rotational and vibrational motion is very rapid (the amplitude of the vibration of the alkyl chains increases with increasing distance from the polar head). Lateral diffusion is also fast (in the direction parallel to the membrane surface). In contrast, transport of the phospholipid from one side of the membrane to the other (flip-flop) is very slow. These properties are typical for the liquid-crystal type of membranes, characterized chiefly by ordering along a single coordinate. When decreasing the temperature (passing the transition or Kraft point, characteristic for various phospholipids), the liquid-crystalline bilayer is converted into the crystalline (gel) structure, where movement in the plane is impossible. 

Fig. 14. O Is level of the Ru02(l 10) surface of single crystalline Ru02 with various surface structures. After [56],...

We and others have been involved in the study of such systems including Cu/Au(lll),85 86 Ag/Au(lll),87 Pb/Ag(lll),88 and Cu/Pt(lll).89 The first three systems involved the use of epitaxially deposited metal films on mica as electrodes.90 92 Such deposition gives rise to electrodes with well-defined single-crystalline structures. In the last case a bulk platinum single crystal was employed. Because of the single-crystalline nature of the electrodes, polarization dependence studies could be used to ascertain surface structure. 

CHX and hydrocarbon wax are, respectively, the active intermediates formed by the hydrogenation of surface carbide and products of FTS formed by chain growth and hydrogenation of CHX intermediates. The hydrocarbon wax can contain molecules with the number of carbon atoms in excess of 100. Bulk carbide refers to a crystalline CoxC structure formed by the diffusion of carbon into bulk metal. Subsurface carbon may be a precursor to these bulk species and is formed when surface carbon diffuses into an octahedral position under the first surface layer of cobalt atoms. 

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. 

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