Electron spectroscopy, analytical method Applications

The modern electronic industry has played a very important role in the development of instrumentation based on physical-analytical methods As a result, a rapid boom in the fields of infrared, nuclear magnetic resonance (NMR), Raman, and mass spectroscopy and vapor-phase (or gas-liquid) chromatography has been observed. Instruments for these methods have become indispensable tools in the analytical treatment of fluonnated mixtures, complexes, and compounds The detailed applications of the instrumentation are covered later in this chapter. 

The most frequently applied analytical methods used for characterizing bulk and layered systems (wafers and layers for microelectronics see the example in the schematic on the right-hand side) are summarized in Figure 9.4. Besides mass spectrometric techniques there are a multitude of alternative powerful analytical techniques for characterizing such multi-layered systems. The analytical methods used for determining trace and ultratrace elements in, for example, high purity materials for microelectronic applications include AAS (atomic absorption spectrometry), XRF (X-ray fluorescence analysis), ICP-OES (optical emission spectroscopy with inductively coupled plasma), NAA (neutron activation analysis) and others. For the characterization of layered systems or for the determination of surface contamination, XPS (X-ray photon electron spectroscopy), SEM-EDX (secondary electron microscopy combined with energy disperse X-ray analysis) and... 

A number of reviews can be consulted for an introduction to the fundamentals both theoretical and practical covering XPS. These include Riggs and Parker (2) and the book by Carlson (3). Electron spectroscopy is reviewed in alternate years in the Fundamental Reviews issue of Analytical Chemistry. The last literature review was published in 1980 (4) and this and previous reviews can be consulted for a coverage of all aspects of the literature of XPS. A number of recent symposia have been held on applications of surface analytical methods in various aspects of materials science such as the symposium on characterization of molecular structures of polymers by photon, electron, and ion probes at the March 1980 American Chemical Society meetings in Houston ( 5) and the International Symposium on Physiochemical Aspects of Polymer Surfaces at this meeting as well as the symposium on industrial applications of surface analysis of which this article is a part. Review articles on various applications of XPS in materials science are listed in Table I. 

Due to the complexity of DOM fractionation has revealed more detailed information on the structural subunits prior to the application of advanced analytical methods. Most effective is the combination of different spectroscopic methods using UV-vis absorbance, fluorescence, 1H- and 13C-nuclear magnetic resonance, and Fourier transform-infrared (FT-IR) spectroscopy. In some studies, also electron paramagnetic resonance spectroscopy (EPR) is used (e.g., Chen et al., 2002). 

The application of analytical methods to speciation measurements in complicated systems has remained rather limited, despite the considerable technological progress during the past 25 years. The characterisation methods (e.g. spectroscopy, nuclear magnetic resonance) are often limited to the study of isolated compounds at relatively high concentrations. They, therefore, necessitate the prior employment of sophisticated separation and pre-concentration methods which introduce severe risks of perturbation. The trace analysis methods are often insensitive to the chemical form of the elements measured (e.g. atomic absorption, neutron activation). Those which possess sufficient element specificity (e.g. electron spin resonance, fluorescence, voltammetry) still require significant development before their full potential can be realised. 

Luminescence spectroscopy is an analytical method derived from the emission of light by molecules which have become electronically excited subsequent to the absorption of visible or ultraviolet radiation. Due to its high analytical sensitivity (concentrations of luminescing analytes 1 X 10 9 moles/L are routinely determined), this technique is widely employed in the analysis of drugs and metabolites. These applications are derived from the relationships between analyte concentrations and luminescence intensities and are therefore similar in concept to most other physicochemical methods of analysis. Other features of luminescence spectral bands, such as position in the electromagnetic spectrum (wavelength or frequency), band form, emission lifetime, and excitation spectrum, are related to molecular structure and environment and therefore also have analytical value. 

Prior to characterization encapsulation must be ensured and clusters formed outside the cavities must be ruled out. Only then can characterization be reliably carried out. A battery of techniques is available for this purpose, such as C,Xe and metal NMR, EXAFS/XANES, XPS, IR and UV-VIS spectroscopy, electron microscopy, ESR, XRD, etc. Among these methods electronic spectroscopy plays an important role. The UV-VIS spectra reflect changes in the oxidation state of the metal as well as structural changes forced by incarceration and so serve as a valuable tool for the ascertainment of intrazeolite complexation. Although vibrational spectroscopy is most frequently applied, sometimes using the IR spectra as fingerprints for identification, it is inadequate to predict the exact structure of the clusters as these spectra maybe different from those in solution or in the sofid state due to interaction with the zeolite matrix. In any case, reliable characterization requires the combined application of complementary analytical methods. 

The penetration mechanism requires the transfer of the aggressive anions from the electrolyte to the metal-oxide interface. The application of surface analytical methods such as X-Ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES), and Secondary Ion Mass Spectroscopy (SIMS) do not clearly support this mechanism. Careful measurements begin with a specimen prepassivated in a solution without any aggressive anions and with their being added later to avoid incorporation during film growth to study their penetration. Eor these conditions. 

The most frequent application of electronic spectroscopy to the study of electrolyte solutions is as a method of quantitative analysis. In such analytical uses the spectroscopy of the system must be considered. In many cases it seems probable that the species seen by electronic spectroscopy are not identical with those measured by other techniques. The problem as related to ion association has been recognised for several years. The basic argument is that for a system of the type... 

In contrast to investigations of adsorption from the gas phase, the number of methods applicable to adsorption from the liquid phase is very small. On the one hand this is caused by the fact that not all methods using either electrons or ions can be applied in situ. In addition the adsorbents are normally powders with no plane surfaces. As a consequence the results of quantitative adsorption measurements are usually calculated from the difference between the liquid concentrations before and after the adsorption process. In principle, any analytical method may be used provided it has sufficient sensitivity pH measurements with a glass electrode and atomic adsorption spectroscopy (AAS) are standard, but complexometry and ion-selective electrodes can also be used. Radiochemical methods are useful in the case of small final concentrations. If electrochemical methods are used, one has to consider that activities, not concentrations, are obtained. In the case of partially soluble adsorbents, such as transition aluminas, their concentration should also be determined, as well as those of all other constituents of the solution, e.g., CO3. ... 

Chourasia, A. R., and D. R. Chopra. Auger Electron Spectroscopy. In Handbook of Instrumental Techniques for Analytical Chemistry, edited by Frank Settle. New York Prentice Hall Professional Reference, 1997. This chapter provides a thorough and systematic description of the principles and practical methods of Auger spectroscopy, including its common applications and limitations. 

The surface properties of polymers are important in many applications and they are dependent on the structure and composition of the ontermost molecular layers. The surface layer thickness involved is typically of the order of a few nanometers. Understanding surface structure-property relationships therefore requires analytical techniques which have this degree of surface sensitivity (or specificity). Two techniques stand out X-ray photoelectron spectroscopy (XPS) (1), also known as ESCA (electron spectroscopy for chemical analysis), and secondary ion mass spectrometry (SIMS) (2). The information provided by these methods is highly complementary and they are frequently used in combination. This article describes the physical bases and anal5dical capabilities of XPS and SIMS and illustrates their application in polymer surface characterization (3). 

Commercial surface analysis systems have been available since around 1970 (1). Most of the early instruments were dedicated to longer-term fundamental research, even if they were located at industrial research centers. However. since the latter part of the 1980s, the most popular surface analytical techniques. Auger electron spectroscopy (AES), secondary-ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS), have gained a greater level of acceptance in industry due to their improved reliability. Surface analysis is now routinely used to solve complex industrial problem.s in both research and quality assurance environments. It has been specifically the move toward the use of these techniques in quality-assurance-type applications that has started to force the development of national/international documentary standards in order to formalize the methods of application of the techniques. 

Of all the techniques that have been developed to analyze surfaces. Auger electron spectroscopy has had the most widespread application. In the field of materials science, it has joined such analytical methods as X-ray diffraction and transmission electron microscopy as a staple of any well-equipped laboratory. It is used in chemistry and materials science to study the composition of solid surfaces and the chemical states of atoms and molecules on those surfaces. Chemists and physicists study the basic Auger transition to help learn about electronic processes in solids. Those interested in developing electronic equipment have been concerned with providing spectrometers with ever-decreasing incident beam diameters that will allow the chemical analysis of a surface on a microscopic scale. It is hoped that this article plus the... 

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