Surface reactivity, tools spectroscopy

Experimental surface science is a meeting ground of chemistry, physics, and engineering.2 New spectroscopies have given us a wealth of information, be it sometimes fragmentary, on the ways that atoms and molecules interact with surfaces. The tools may come from physics, but the questions that are asked are very chemical, e.g., what is the structure and reactivity of surfaces by themselves, and of surfaces with molecules on them ... 

It is hoped that this review is a useful introduction to the characteristics of semiconductor surfaces and molecular modeling approaches to address their structure, stability, and reactivity. These materials are complex, and an impression of the current utility and pitfalls of modeling to capture the important processes operative at these surfaces should be evident. The combination of ab initio modeling and experiment is clearly an incredibly powerful tool in this area. The ability of the calculations and the surface microscopies and spectroscopies to elucidate a convergent description is remarkable, and the connection between the two is quite natural. Much more information stands to be gained when the two methods are applied in parallel, and certainly more concretely than could be gained from either approach alone. The calculations allow observables to be explained in useful physical terms, and nonobservables to be quantified. At the scale of atoms and molecules, this approach is indispensable. 

In addition to the many applications of SERS, Raman spectroscopy is, in general, a usefiil analytical tool having many applications in surface science. One interesting example is that of carbon surfaces which do not support SERS. Raman spectroscopy of carbon surfaces provides insight into two important aspects. First, Raman spectral features correlate with the electrochemical reactivity of carbon surfaces this allows one to study surface oxidation [155]. Second, Raman spectroscopy can probe species at carbon surfaces which may account for the highly variable behaviour of carbon materials [155]. Another application to surfaces is the use... 

The objective of the work presented here is to combine activity studies using a model reaction with STM and AFM studies on model catalysts and to determine structural correlations between catalytic activity and morphology. Other characterization tools are also used to determine compositional effects induced by pretreatment or the reaction. The model reaction used is the hydrogenation of 1,3 butadiene hydrogenation due to its high reactivity on low-surface area Pd model catalysts and its well-studied mechanism [17-19]. X ray photoelectron spectroscopy (XPS) was used to determine surface composition. 

The hexapole technique has been extensively exploited for the study of oriented open shell molecules such as OH (see Ref [46] and references therein) and NO (see Ref [47] and references therein), the latter also for scattering on surfaces [48]. This is a very important topic, because the basic tool for enhancement of chemical reactivity is catalysis at surfaces. In Ref [49], for examples, the oxidation of Si (001) induced by incident energy of O2 molecules is studied by synchrotron radiation photoemission spectroscopy and mass spectrometry, a process of a kind which may show propensities regarding molecular orientation of O2 as it impinges on the surface, possibly controlled by techniques of the kind described in previous sections. 

The formation and reactivity of surface intermediates over three-way catalysts are important subjects in designing automobile exhaust catalysts. The high temperature NO-CO and NO-CO-O2 reactions produce isocyanate surface intermediates (-NCO) and release N2O intermediate products depending on, for example, how the catalyst surface is pretreated before the NO and CO adsorption [2]. Infrared spectroscopy is an excellent tool to investigate the formation of these kind of surface intermediates. With IR very low concentrations of surface compounds can be detected under reaction conditions. 

Infrared spectroscopy has previously been shown to be a powerful tool for studying reactions at surface acid sites using a variety of surface-sorbed probe molecules (12, 13, 21,22). For example, the protonation of NH to when adsorbed at Bronsted sites can be clearly distinguished from NH retained at Lewis sites using IR (12). Similarly, the formation of pyridinium ions upon the adsorption of pyridine at Bronsted sites is spectrally distinct from pyridine sorbed at Lewis sites (12). We have taken advantage of IR spectroscopy to identify and quantify the degradation products, TriPB and DPBA, as pathway-specific probes of TPB reactivity at respective Bronsted and Lewis acid sites of phyllosilicates (13). 

A high-speed beam of non-reactive noble gas atoms then strikes the surface, raising the effective temperature and pressure at the surface—simulating the reaction conditions the group wants to study, but only at the point at which the beam hits the surface. Overall, the pressure is still low enough to allow diagnostic tools like Auger spectroscopy and electron diffraction to function. 

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