Surface adlayer

One class of large molecules that was investigated relatively early was liquid crystals [37, 38], and in particular the group 4-n-alkyl-4 -cyanbiphenyl (mCB). These molecules fonu a highly crystalline surface adlayer, and STM images clearly show the characteristic shape of the molecule (figure B 1.19.8). 

WeinertM, Watson RE. 1995. Core-level shifts in bulk alloys and surface adlayers. Phys Rev B 51 17168-17180. 

Correlations between surface species and emitted secondary ions are based on characterization of the surface adlayer by adsorption and thermal desorption measurements. It is shown that the secondary ion ratios RuC+/Ru+ and R CTVRuJ can be quantitatively related to the amount of nondesorbable surface carbon formed by the dissociative adsorption of ethylene. In addition, emitted hydrocarbon-containing secondary ions can be directly related to hydrocarbon species on the surface, thus allowing a relatively detailed analysis of the hydrocarbon species present. The latter results are consistent with ejection mechanisms involving intact emission and simple fragmentation of parent hydrocarbon species. 

From the mode equation and equation (38), the waveguide sensitivity for both cover refractive index and the surface adlayer changes can be derived (three-layer planar waveguide). The derivation is given in detail in [7] and here only the results... 

Fig. 6 Theoretical sensitivities of waveguides depending on the waveguide thickness, (a) to cover refractive index changes, (b) to surface adlayer changes with ris = 1.52, n = 2.1, ric = 1.333 at = 675 nm [8]...

Adzic, R.R. and Wang, J.X., Structures of surface adlayers and oxygen reduction kinetics, Solid State Ionics, 150, 105, 2002. 

Such fundamental knowledge about the microscopic processes on the gas-solid interface is also necessary for optimization of many catalytic processes. A statistical mechanical approach, which enables the solution of the many-body problem constituted by the adsorbate layer on the catalytic surface, is essential in the case when lateral interactions between adatoms and molecules are significant. In such cases, non-ideal surface adlayer mixing is often important and the adsorbates form islands on the surface. Hence, microscopic simulations of catalytic processes are necessary to develop an ab-initio approach to kinetics in catalysis. 

PET is the key feature of many other photo-oxidations involving aromatic substrates. It has been shown, for example, that pyrene and anthracene which are covalently attached to silica, gold or indium-doped tin oxide (ITO), undergo a photo-oxidation forming dihydroxy/dione derivatives. The reaction involves 02, formed by ET between excited pyrene, or anthracene, and O2, and it is suggested that the implications of such a photodegradation need to be considered when polycyclic aromatic hydrocarbons (PAHs) are used as spectroscopic probes in surface adlayers. The redox photosensitized amination of 1,2-benzo-1,3-cycloalkadienes, arylcyclopropanes, and quadricyclane with ammonia and primary amines, using 1,2,4-triphenylbenzene (1,2,4-TPB) or 2,2 -methylenedioxy-1,1 -binaphthalene in the presence of m- or p-dicyano-benzene (DCB), has been described (Scheme 51). The process involves the formation of the radical cation of 1,2,4-TPB, for example, by PET to the DCB, followed by hole transfer from the radical cation to the substrate, the latter... 

XPS data (Xable 2 and 3) show good agreement between molecular stoichiometry and elemental distribution in surface adlayers. Deviations between the experimental and theoretical data are attributed to contamination. 

Coadsorption suppresses surface reactions that require sites consisting of several metal atoms by blocking. The close proximity of coadsorbate molecules may lead to steric hindrance effects, reducing translational or rotational motion. Short-range lateral effects may enhance as well as decrease the adsorbate-surface interaction strength. Enantiomeric selectivity as well as selective oxidation are examples of reactions that are sensitive to the composition of the surface adlayer. In the former case the selectivity is enhanced due to steric interactions. In the latter case the chemical nature of adsorbed surface atoms changes with surface adatom concentration. 

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