Spectroscopy, common techniques

Analysis of Surface Elemental Composition. A very important class of surface analysis methods derives from the desire to understand what elements reside at the surface or in the near-surface region of a material. The most common techniques used for deterrnination of elemental composition are the electron spectroscopies in which electrons or x-rays are used to stimulate either electron or x-ray emission from the atoms in the surface (or near-surface region) of the sample. These electrons or x-rays are emitted with energies characteristic of the energy levels of the atoms from which they came, and therefore, contain elemental information about the surface. Only the most important electron spectroscopies will be discussed here, although an array of techniques based on either the excitation of surfaces with or the collection of electrons from the surface have been developed for the elucidation of specific information about surfaces and interfaces. 

Mass spectrometry, infrared spectroscopy, and nuclear magnetic resonance spectroscopy are techniques of structure determination applicable to all organic molecules. In addition to these three generally useful methods, there s a fourth—ultraviolet (UV) spectroscopy—that is applicable only to conjugated systems. UV is less commonly used than the other three spectroscopic techniques because of the specialized information it gives, so we ll mention it only briefly. 

It is my opinion that this approach has considerable merit, provided that the questions posed in the problems are wisely selected, as indeed they are in this text. The authors themselves are well versed in natural-product chemistry, an area that presents a wide array of small molecule structural problems. They are therefore concerned that the reader reach the practical goal of applying the full power of NMR spectroscopy to problems of this type. To this end they have selected problems that address methods for solving structures as well as those that pertain to basic theory. The authors have wisely made a point of treating the more widely used ID and 2D experiments in considerable detail. Nevertheless, they also introduce the reader to many of the less common techniques. 

In this chapter we have limited ourselves to the most common techniques in catalyst characterization. Of course, there are several other methods available, such as nuclear magnetic resonance (NMR), which is very useful in the study of zeolites, electron spin resonance (ESR) and Raman spectroscopy, which may be of interest for certain oxide catalysts. Also, all of the more generic tools from analytical chemistry, such as elemental analysis, UV-vis spectroscopy, atomic absorption, calorimetry, thermogravimetry, etc. are often used on a routine basis. 

Raman spectroscopy comprises a family of spectral measurements based on inelastic optical scattering of photons at molecules or crystals. It involves vibrational measurements as well as rotational or electronic studies and nonlinear effects. Following, Raman will be used in the established but slightly inaccurate way as a synonym for the most important and most common technique of the family, linear vibrational Raman scattering. 

The elemental composition, oxidation state, and coordination environment of species on surfaces can be determined by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) techniques. Both techniques have a penetration depth of 5-20 atomic layers. Especially XPS is commonly used in characterization of electrocatalysts. One common example is the identification and quantification of surface functional groups such as nitrogen species found on carbon-based catalysts.26-29 Secondary Ion Mass spectrometry (SIMS) and Ion Scattering Spectroscopy are alternatives which are more surface sensitive. They can provide information about the surface composition as well as the chemical bonding information from molecular clusters and have been used in characterization of cathode electrodes.30,31 They can also be used for depth profiling purposes. The quantification of the information, however, is rather difficult.32... 

Time-resolved UV-vis spectroscopy is the most common technique and has been widely used, but other time-resolved spectroscopies such as IR and EPR have become available as well. 

Three common techniques used are transmission electron microscopy together with electron diffraction, powder X-ray diffraction, and optical absorption (or transmission) spectroscopy. 

Subsequently, fluorescent MIPs for cGMP were fabricated [46 18, 66, 67]. For that, 1,3-diphenyl-6-vinyl-1 //-pyrazolo 3.4-/ quinoline (PAQ) was introduced as the fluorescent indicator to interact with cGMP in a thin-layer fluorescent MIP chemosensor. Both steady-state (Fig. 1) and time-resolved fluorescence spectroscopy were used as two independent analytical techniques for investigation of the chemosensor properties in the presence of cGMP. Steady-state fluorescence spectroscopy is a common technique applied to MIP sensing. Nevertheless, the use of time-resolved fluorescence spectroscopy combined with microscopy was a new approach to MIP sensing. 

The most common techniques for testing electrodes are sweep voltammetry, galvanostatic poten-tiometry, rotating disk electrochemistry, and impedance spectroscopy. Detailed information about these techniques may be found in most classical electrochemical textbooks [6-13], and we will present here the basics of these techniques. 

Optical spectroscopies. These techniques are the least intrusive in situ plasma diagnostic methods. The most commonly used techniques are emission spectroscopy, absorption spectroscopy, laser-induced fluorescence. 

Several methods have been used to determine the surface acidity of solid acids, but each method has its limitations. Common methods are titration with the Hammett indicators, temperature-programmed desorption (TPD), adsorption microcalorimetry, catalytic test reactions, and IR and NMR spectroscopies. These techniques exhibit several advantages and disadvantages. 

Perrette et al. (2000) measured concentration by ESR spectroscopy and found that the Mn varied with other precipitation indicators such as color banding. ESR spectroscopy is an intrinsically low-resolution measurement. Cathodoluminescence imaging should reveal Mn banding. Cathodoluminescence imaging is a common technique in sedimentary petrography but does not seem to have been applied to speleothems. 

Differential scanning calorimetry (DSC), X-ray diffraction (XRD), and infrared spectroscopy are the common techniques used in the characterization of the structure of the congealed solid. Thermal analytic methods, such as DSC and differential microcalorimetric analysis (DMA), are routinely used to determine the effect of solutes, solvents, and other additives on the thermomechanical properties of polymers such as glass transition temperature (Tg) and melting point. The X-ray diffraction method is used to detect the crystalline structure of solids. The infrared technique is powerful in detecting interactions, such as complexation, reaction, and hydrogen bonding, in both the solid and solution states. 

The technique of AC impendance spectroscopy, one of the most common techniques in aqueous and solid-state electrochemistry, was used recently to confirm the formation of the effective double layer on metal surfaces interfaced with YSZ [43,95]. An example for the case of Pd/YSZ is shown in Figure 20. The semicircle labeled Ci is associated with the charge-transfer reaction... 

Specific spectroscopic techniques are used for the analysis of polymer surface (or more correctly of a thin layer at the surface of the polymer). They are applied for the study of surface coatings, surface oxidation, surface morphology, etc. These techniques are typically done by irradiating the polymer surface with photons, electrons or ions that penetrate only a thin layer of the polymer surface. This irradiation is followed by the absorption of a part of the incident radiation or by the emission of specific radiation, which is subsequently analyzed providing information about the polymer surface. One of the most common techniques used for the study of polymer surfaces is attenuated total reflectance in IR (ATR), also known as internal reflection spectroscopy. Other techniques include scanning electron microscopy, photoacoustic spectroscopy, electron spectroscopy for chemical analysis (ESCA), Auger electron spectroscopy, secondary ion mass spectroscopy (SIMS), etc. 

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