Electronic spectroscopy disadvantages

Each type of mass spectrometer has its associated advantages and disadvantages. Quadrupole-based systems offer a fairly simple ion optics design that provides a certain degree of flexibility with respect to instrument configuration. For example, quadrupole mass filters are often found in hybrid systems, that is, coupled with another surface analytical method, such as electron spectroscopy for chemical analysis or scanning Auger spectroscopy. 

The most widely used techniques for surface analysis are Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), Raman and infrared spectroscopy, and contact angle measurement. Some of these techniques have the ability to determine the composition of the outermost atomic layers, although each technique possesses its own special advantages and disadvantages. 

We shall concern ourselves here with the use of an X-ray probe as a surface analysis technique in X-ray photoelectron spectroscopy (XPS) also known as Electron Spectroscopy for Chemical Analysis (ESCA). High energy photons constitute the XPS probe, which are less damaging than an electron probe, therefore XPS is the favoured technique for the analysis of the surface chemistry of radiation sensitive materials. The X-ray probe has the disadvantage that, unlike an electron beam, it cannot be focussed to permit high spatial resolution imaging of the surface. 

As a surface analytical tool, SIMS has several advantages over X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). SIMS is sensitive to all elements and isotopes in the periodic table, whereas XPS and AES cannot detect H and He. SIMS also has a lower detection limit of 10 5 atomic percent (at.S) compared to 0.1 at.S and 1.0 at.% for AES and XPS, respectively. However, SIMS has several disadvantages. Its elemental sensitivity varies over five orders of magnitude and differs for a given element in different sample matrices, i.e., SIMS shows a strong matrix effect. This matrix effect makes SIMS measurements difficult to quantify. Recent progress, however, has been made especially in the development of quantitative models for the analysis of semiconductors [3-5]. 

Vibrational spectroscopy is a powerful tool for the study of molecular structure and dynamics. The typical vibrational frequency range of this spectroscopy is 100-4000 cm, which corresponds to the energy range 0.3-12 kcal/mol. Because the resolution of vibrational spectroscopy is on the order of 5 cm , the band shift on this order corresponds to a 0.02 kcal/mol. Vibrational transitions are correlated with specific vibrational motions by inspection of the transition frequencies. From identification of these fingerprint vibrational modes, conclusions can be drawn on specific structural motifs in the molecules. Vibrational transitions have bandwidths typically smaller (10-20 cm ) than those from electronic transitions (typically 200-2000 cm ), and it is thus less probable that different transition bands overlap in vibrational spectroscopy than in electronic spectroscopy. In addition, small molecular species may always be probed through their vibrations, and electronic transitions. Major disadvantages of vibrational spectroscopy, on the other hand, are the inherent lower cross sections of vibrational transitions and the frequent overlap of the absorption bands with those of the solvent [10]. 

XPS, or as it is sometimes called electron spectroscopy for chemical analysis (ESCA), allows characterization of the elemental composition of the top 10-30 A of a material. Its disadvantage is that it is a high-vacuum technique and hence can only be used for the study of materials whose structure is not sensitive to the application of a vacuum. 

Various planar membrane models have been developed, either for fundamental studies or for translational applications monolayers at the air-water interface, freestanding films in solution, solid supported membranes, and membranes on a porous solid support. Planar biomimetic membranes based on amphiphilic block copolymers are important artificial systems often used to mimic natural membranes. Their advantages, compared to artificial lipid membranes, are their improved stability and the possibility of chemically tailoring their structures. The simplest model of such a planar membrane is a monolayer at the air-water interface, formed when amphiphilic molecules are spread on water. As cell membrane models, it is more common to use free-standing membranes in which both sides of the membrane are accessible to water or buffer, and thus a bilayer is formed. The disadvantage of these two membrane models is the lack of stability, which can be overcome by the development of a solid supported membrane model. Characterization of such planar membranes can be challenging and several techniques, such as AFM, quartz crystal microbalance (QCM), infrared (IR) spectroscopy, confocal laser scan microscopy (CLSM), electrophoretic mobility, surface plasmon resonance (SPR), contact angle, ellipsometry, electrochemical impedance spectroscopy (EIS), patch clamp, or X-ray electron spectroscopy (XPS) have been used to characterize their... 

Complementary analytical studies of the surface films using Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edges structures (XANES) [7, 8] lead to an accurate description of the antiwear film mainly composed of amorphous Ee/Zn poly(thio)phosphate embedding some nanocrystallites of ZnO and ZnS. The chemical reaction involved in the build-up of the tribo-film were recently interpreted with new theoretical approaches (hard and soft acid-base theory) [9, 10]. The action process of anti wear additives such as ZDDP presents two disadvantages ... 

There are now several different types of machines that are all capable of microanalysis. All have advantages and disadvantages, but the choice of which to use is often governed by expense and availability to a particular institution. Electron probe microanalysis is by far the most popular, but here particle-induced X-ray emission (PIXE), the laser microprobe mass analyzer (LAMMA), electron energy loss spectroscopy (EELS), and secondary ion mass spectrometry (SIMS) are also considered. 

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