Surface analysis data interpretation

Capacitance and surface tension measurements have provided a wealth of data about the adsorption of ions and molecules at electrified liquid-liquid interfaces. In order to reach an understanding on the molecular level, suitable microscopic models have had to be considered. Interpretation of the capacitance measurements has been often complicated by various instrumental artifacts. Nevertheless, the results of both experimental approaches represent the reference basis for the application of other techniques of surface analysis. 

Imaging of Surfaces—Analysis of Surface Morphology. Several important techniques can help answer the question what does the surface look like This question is often the first one to be posed in the characterization of a new surface or interface. Physical imaging of the surface is necessary to distinguish the relevant features important for understanding the whole surface and is essential for accurate interpretation of data from other surface analysis techniques which might later be applied to a more limited region of the surface or interface. 

Generally, theoretical analysis and experimental interpretation of surface compositional data assume a homogeneous glass. At times this assumption is not valid. 

A selection of papers on the general theme on soil, surface, and groundwater contamination, environment pollution and human health, and data interpretation and management are published in a special issue of Geochemistry Exploration, Environment, Analysis Special Issue Environmental Geochemistry , edited by B. De Vivo, J. A. Plant, and A. Lima. 

Although both the laboratory and industrial scale materials science of catalysts requires an integrated approach as already mentioned above, it is customary to classify the characterization methods by their objects and experimental tools used. I will use the object classification and direct the introductory comments to analysis, primarily elemental and molecular surface analysis, determination of geometric structure, approaches toward the determination of electronic structure, characterization by chemisorption and reaction studies, determination of pore structure, morphology, and texture, and, finally, the role of theory in interpreting the often complex characterization data as well as predicting reaction paths. 

All exposure environments designed to aid in the study of materials degradation in LEO have drawbacks that must be taken into account when trying to interpret either post-exposure analysis data or data collected in situ. Because of the difficulty of controlling an exposure environment, many conclusions about the mechanisms by which atomic oxygen attacks a surface and assists in the oxidation and erosion of materials have been reached less systematically than would be desired. 

For microporous materials there is considerable debate on how to interpret surface area data due to the presence of micropores. Usually BET data are reported when one purchases a zeolite from a commercial vendor. The specific value of the BET measurement may give some indication of the relative surface area of the zeolite. Several experimental methods have been developed to collect BET data and many different equations have been used to model adsorption data. There are several discussions in the literature on various methods that have been used to analyze adsorption data by Broekhoff, et al.2 and Masthan et al. There is considerable debate on which method is the best for measuring BET data, however, there is good consensus that pore size distributions can be measured accurately with little problem in data analysis. 

The on-line coupling between TLC and mass spectrometry provides a powerful combination for the detection and identification of substances separated by a planar chromatographic method. The on-line coupling between these two methods has to overcome the problem of vaporizing and introducing the sample into the mass spectrometer. Different methods are reported in the literature, but the analytical principle is the same the sample is ionized from the layer surface by means of a laser beam, under vacuum, and in the presence of an energy-buffering matrix. Once the ions are transferred into the mass spectrometer, more sophisticated methods can be applied for data analysis and interpretation, e.g., MS-MS. 

These system-specific advantages facilitate the analysis and Interpretation of experimental results obtained by different in situ surface analytical techniques. Therefore, most experimental data has been collected in the Pb UPD system. 

It should be mentioned, however, that surface inhomogeneities of different dimensionality (cf. Section 2.1) significantly influence the kinetics of metal electrodeposition and the time-dependent surface morphology. Therefore, an exact analysis of corresponding EIS spectra is rather difficult. The necessary presumptions of stationarity and linearity for EIS measurements and quantitative interpretation of EIS data are often violated. The lack of direct local information on surface dynamics strongly hinders a quantitative analysis of the impedance behavior of time-dependent systems. Such considerations have been mainly disregarded in previous EIS data interpretations. In future, a combination of EIS measurements with in situ local probe... 

Experiments in the carbonization of coal to produce low sulfur char were carried out and evaluated by means of a three-step procedure. Carbonization runs were flrst conducted to obtain data at various combinations of the three major independent variables. These data were then used to develop an empirical mathematical model that described the carbonization system. Finally, response surface analysis was used to interpret the empirical model and to predict the relationship between process variables and char yield and quality. 

P. A. Linfors, "Computer Curve Fitting of ESCA Data to Aid Interpretation," 3rd Symposium on Applied Surface Analysis, Dayton, OH., 1981. 

Ab initio molecular orbital calculations have played a central role in the analysis and interpretation of X-ray photoemission data obtained on the PMDA-ODA polyimide surface 1 4. The repeat unit of the PMDA-ODA polyimide is shown in Figure 1 and is constructed from planar pyromellitimide (PMDA) and diphenyl ether segments. An understanding of the XPS data and its relationship to the surface chemistry prior to the deposition of any metal is crucial with respect to the interpretation of changes in the XPS data which signify important metal-polymer chemistry that occurs upon formation of the interface. 

For surface analysis all SECM modes—the feedback, generation/collection, and direct modes—have been used to visualize lateral differences in heterogeneous electron transfer properties. At this point, we shall briefly review a few aspects of surface imaging concerning the acquisition and interpretation of data that are relevant for most experiments before presenting individual studies. Details of SECM imaging are discussed in Chapter 4. 

The operation and maintenance of ESCA equipment and interpretation of its data are quite complex. Samples intended for ESCA and other surface analysis methods should be handled carefully because minute contamination can mask the surface structure... 

Future studies will be focused on the development and improvement of numerical methods for pore size and surface analysis. It is expected that novel carbons with uniform and ordered nanopores would play an important role in the development and examination of these methods. Another important issue in the characterization of nanoporous carbons is the elaboration of simple methods based on the Uquid/solid adsorption data. Although interpretation of these data is more complex, they are useful for investigation of heterogeneous nanoporous carbons [170,171,175, 177]. 

In the advanced state of delamination, two zones of different activity can be located underneath the organic coating. The shift of the corrosion potential close to the rather anodic potential of the intact interface marks the front of the advancing cathode. Behind this cathodic area the steep slope marks the front of anodic undermining. Fiirbeth and Stratmann proved this interpretation of the SKP data with cross-sectional and surface analysis of the delaminated area [86]. 

Depending on the viscosity of liquid and its expected flash point range, one of the above methods is chosen as described in detail elsewhere. It should be additionally noted that if the flash point method uses continuous heating, it is not suitable for testing mixtures of flammable substances because their vapor concentrations are not representative of equilibrium eonditions. One of the weaknesses of flash point analysis is that the flame is well above the liquid surface therefore full vapor concentration is not attained. Many cases exist where a flash point cannot be detected but the material does form flammable mixtures. Before a method is chosen and a data interpretation made full information on the test procedure should be studied in detail and the proper authorities should be eonsulted to define safe practices for a particular material. 

Temperature-dependent interfacial structural changes at temperatures of 100 K and UHV conditions that were observed via HREELS vibrational analysis were interpreted as molecular reorientation on the surface the difference in emission signals at 300 and 100 K was also attributed to ion rearrangement at the interface, and not to ionic liquid decomposition [19]. The overall results from elastic emission and electron energy loss signals confirmed again that both cation and anions are found on the top layers irrespective of temperature, but HREELS data alone could not provide specific details on the exact reorientation [19]. 

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