Surface analytical techniques spectroscopy

X-ray photoelectron spectroscopy (XPS) is currently the most widely used surface-analytical technique, and is therefore described here in more detail than any of the other techniques. At its inception hy Sieghahn and coworkers [2.1] it was called ESCA (electron spectroscopy for chemical analysis), hut the name ESCA is now considered too general, because many surface-electron spectroscopies exist, and the name given to each one must be precise. The name ESCA is, nevertheless, still used in many places, particularly in industrial laboratories and their publications. Briefly, the reasons for the popularity of XPS are the exceptional combination of compositional and chemical information that it provides, its ease of operation, and the ready availability of commercial equipment. 

Much of the pioneering work which led to the discovery of efficient catalysts for modern Industrial catalytic processes was performed at a time when advanced analytical Instrumentation was not available. Insights Into catalytic phenomena were achieved through gas adsorption, molecular reaction probes, and macroscopic kinetic measurements. Although Sabatier postulated the existence of unstable reaction Intermediates at the turn of this century. It was not until the 1950 s that such species were actually observed on solid surfaces by Elschens and co-workers (2.) using Infrared spectroscopy. Today, scientists have the luxury of using a multitude of sophisticated surface analytical techniques to study catalytic phenomena on a molecular level. Nevertheless, kinetic measurements using chemically specific probe molecules are still the... 

The application of surface analytical techniques, most notably X-ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES), or its spatially resolved counterpart. Scanning Auger Microanalysis (SAM), is of great value in understanding the performance of a catalyst. However, the results obtained from any of these techniques are often difficult to interpret, especially when only one technique is used by itself. 

IR spectroscopy, one of the few surface analytical techniques not requiring a vacuum, provides a large amount of molecular information. The absorption versus frequency characteristics are obtained when a beam of IR radiation is transmitted through a specimen. IR is absorbed when a dipole vibrates naturally at the same frequency as the absorber, and the pattern of vibration is unique for a given molecule. Therefore, the components or groups of atoms that are absorbed into the IR at specific frequencies can be determined, allowing identification of the molecular structure. 

In addition to the electrochemical techniques, many surface analytical techniques are constantly in use, such as ellipsome-try for the surface thin oxide thickness, multiple reflection infrared spectroscopy (MIR), and X-ray photoelectron spectroscopy (XPS) for surface layer composition, total reflection X-ray fluorescence spectroscopy (TXRFS) for the metal surface contaminants, and naturally atomic force microscopy (AFM) for the surface roughness profile. 

X-Ray Photoelectron Spectroscopy (XPS). This technique is also known as electron spectroscopy for chemical analysis (ESCA), and as this name implies, it is a surface analytical technique. At present it is probably the most versatile and generally applicable surface spectroscopic technique. It is called XPS because of the type of beam used to study the interfacial region, that is, X-rays. These X-rays consist of monochromatic radiation—radiation of a given energy—emitted by a metal target bombarded by an electron beam of several kiloelectron volts of kinetic energy... 

Passivation of active metals to hydrogen reaction has been recognized as an important problem in basic metal-hydrogen studies, especially in their technological application to various situations. Few investigations have addressed these difficulties. The advent of modern surface analytical techniques such as photoelectron spectroscopyy Auger electron spectroscopy, and ion spectrometry offer a tremendous opportunity to attack the passivation question. Each of these techniques is discussed with regard to their capabilities and application to hydride kinetics. 

The interaction of cesium ions with feldspars at 150°C and 200°C has been studied in distilled water, granite groundwater and saline solution Pollucite, CsAlSi206, was identified by infrared spectroscopy, and was formed as a cubic crystalline phase. Surface analytical techniques (XPS, SAM, SIMS and SEM/ EDX) show Cs to be sorbed onto the mineral surfaces and alteration products. The mechanism of pollucite formation and its relevance to cesium transport/ retardation in the near field of a nuclear waste-disposal vault is discussed. 

During the early years of nonaqueous battery development the lack of sensitive surface analytical techniques and the availability of only limited capability impedance spectroscopy techniques precluded understanding much about the nature of the interface between the electrolyte and active materials. It was not always... 

The analysis of corrosion scale or product may be done by wet chemical methods such as spectrophotometry or atomic absorption spectrophotometry in cases where the removal of corrosion scale is permitted, or by surface analytical techniques such as X-ray photoelectron spectroscopy, Auger electron spectroscopy, electron microprobe analysis, by energy dispersive X-ray analysis in the case of samples which need to be preserved. 

The interface between plastic and wood fibres strongly influences the mechanical properties of a plastic/wood fibre composite. A means for evaluating the effectiveness of surface treatment on the wood fibres in the PVC/wood fibre composites is presented that investigated the adhesion between PVC and laminated wood veneers. Wood veneers were first treated with gamma-aminopropyltriethoxysilane, dichlorodiethylsilane, phthalic anhydride, and maleated PP for surface modification. The chemical modification made on the wood surfaces was then characterised by different complementary surface analytical techniques X-ray photoelectron spectroscopy and surface tension measurements. 63 refs. 

J.C. Riviere, Surface Analytical Techniques, Oxford University Press (1990). (Discusses a variety of surface spectroscopies.)... 

Surface analytical techniques. A variety of spectroscopic methods have been used to characterize the nature of adsorbed species at the solid-water interface in natural and experimental systems (Brown et al, 1999). Surface spectroscopy techniques such as extended X-ray absorption fine structure spectroscopy (EXAFS) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) have been used to characterize complexes of fission products, thorium, uranium, plutonium, and uranium sorbed onto silicates, goethite, clays, and microbes (Chisholm-Brause et al, 1992, 1994 Dent et al, 1992 Combes et al, 1992 Bargar et al, 2000 Brown and Sturchio, 2002). A recent overview of the theory and applications of synchrotron radiation to the analysis of the surfaces of soils, amorphous materials, rocks, and organic matter in low-temperature geochemistry and environmental science can be found in Fenter et al (2002). 

Surface analytical techniques such as Auger electron spectroscopy (27), X-ray photoelectron spectroscopy (28), and secondary-ion mass spectrometry (29) have been used to study LB films. Synchrotron radiation is a particularly powerful probe enabling X-ray near-edge structure and extended X-ray absorption fine structure to be measured. Angle-resolved photoemission studies (30) confirmed the existence of a one-dimensional energy band along the (CH2)jc chain in a fatty acid salt film. 

In addition to the electrochemical techniques, many insitu and exsitu surface analytical techniques are used in studies of silicon electrodes, such as ellipsometry for determining thin surface film thickness, ° infrared spectroscopy for surface adsorption, 260,424 surface composition, and for... 

The susceptibility of solid surfaces to contamination often results in a requirement for an ultrahigh vacuum (UHV) chamber for preparation and observation of particular samples. For many materials, including metals such as platinum and nickel, adsorption of hydrocarbons and chemisorption of oxygen are quite fast at atmospheric pressure, and the surface must be isolated in UHV to prevent rapid degradation. In addition, a sample in UHV may be subjected to surface analytical techniques such as X-ray photoelectron and Auger spectroscopy to verify or corroborate Raman results. As a result, much of the early and well-characterized surface Raman experiments were carried out in UHV chambers operating below 10 torr (12). 

Energy-dispersive X-ray microanalysis Surface analytical techniques Scanning near-field optical microscopy Scanning thermal microscopy Atomic force microscopy X-ray photoelectron spectroscopy... 

Static secondary ion mass spectroscopy (SSIMS) ranks with XPS as one of the principal surface analytical techniques. Treatment of polymer surfaces to improve their properties with respect to wetting or water repulsion and to adhesion, is by now a standard procedure. The treatment is designed to change the chemistry of the outermost groups in the polymer without affecting bulk properties. One popular surface treatment is plasma etching. The use of SSIMS is most amenable to the surface evaluation of such treated materials. 

Mass-spectrometry principles and techniques have been employed in other kinds of surface studies in which sample atoms are sputtered by interaction with a laser beam or by RF glow discharges. These approaches are more highly specialized, but it should be clear that mass spectrometry is an important tool in surface chemistry. The student should compare SIMS and ISS with other surface analytical techniques such as ESCA, Auger spectroscopy, electron microprobe, and low-energy electron diffraction (see Chaps. 14 and 15). 

Conventional electrochemical methods provide a vast amount of kinetic and mechanistic information about heterogeneous redox processes. However, it is desirable to supplement this with the molecular structural information that can now be provided by several in-situ surface analytical techniques [1, 2]. Of the techniques available, infrared spectroscopy is well suited for this task since the spectral data can yield valuable information on the identity as well as the reactivity of the interfacial species. This is especially true when examining multistep reactions involving adsorbed intermediate. 

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