Instrumental techniques resolution capabilities

GC-FTIR, GC-AED, GC-ICP-MS, cf. Chapter 7), fast GC separations (1996) and most recently the development of sophisticated injectors with temperatureprogramming capability and high-resolution systems (GC-ToFMS). As a result, modem GC systems are quite advanced (Scheme 4.3) and GC is one of the most widely applied instrumental techniques. 

The use of Atomic Force Microscopy for the characterization of oxide materials is still limited but the high resolution capabilities of the method show promise for the study of a wide variety of surfaces. Both the principles of the technique and the instrumentation must be advanced so that a wider range of morphologies can be studied with resolution approaching that achieved at present on relatively smooth surfaces. 

More detailed surface features and topography can be revealed by scanning tunneling microscopy (STM) or atomic force microscopy (AFM). The instruments employing these techniques are capable of resolution at the atomic level. Recent efforts have also shown the feasibility of manipulating and rearranging atoms on the surface. The techniques do not require vacuum and can even be used in solution to study such processes as reactions taking place at the surfaces of electrodes, corrosion, or precipitation/dissolution phenomena. 

For a solid, XPS probes 2 to 20 atomic layers deep, depending of the KE of the ejected electron, the angle w.r.t., the solid surface of detection, and the material. XPS is therefore a true surface technique. If measurement is made as a function of angle, depth distribution information is available over the depth probed. XPS is also used with sputter depth profiling to go beyond these depths. Modern laboratory XPS instruments can providepracticalldXtrA resolution capability down to the 10 to 20 pm range. Specialized systems can go lower, but acquisition time becomes very long. 

The SNMS instrumentation that has been most extensively applied and evaluated has been of the electron-gas type, combining ion bombardment by a separate ion beam and by direct plasma-ion bombardment, coupled with postionization by a low-pressure RF plasma. The direct bombardment electron-gas SNMS (or SNMSd) adds a distinctly different capability to the arsenal of thin-film analytical techniques, providing not only matrbe-independent quantitation, but also the excellent depth resolution available from low-energy sputterii. It is from the application of SNMSd that most of the illustrations below are selected. Little is lost in this restriction, since applications of SNMS using the separate bombardment option have been very limited to date. 

Modern instruments capable of obtaining excitation-emission matrices (EEMs) allow use of new data-analysis techniques to resolve overlapped spectra. Resolution techniques such as the ratio method (28) and others (29,30) may provide further differentiation of the components present in the phases separated by solvent extraction. 

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