Electron spectroscopy of chemical analysis ESCA

Surface Chemical Analysis. Electron spectroscopy of chemical analysis (ESCA) has been the most useful technique for the identification of chemical compounds present on the surface of a composite sample of atmospheric particles. The most prominent examples Include the determination of the surface chemical states of S and N in aerosols, and the investigation of the catalytic role of soot in heterogeneous reactions involving gaseous SO2, NO, or NH3 (15, 39-41). It is apparent from these and other studies that most aerosol sulfur is in the form of sulfate, while most nitrogen is present as the ammonium ion. A substantial quantity of amine nitrogen also has been observed using ESCA (15, 39, 41). 

Fig. 9.1 The schematic of first liquid electron spectroscopy of chemical analysis (ESCA) designed by the Siegbahn group. Reproduced from refs. [18-20]...

Madey and co-workers followed the reduction of titanium with XPS during the deposition of metal overlayers on TiOi [87]. This shows the reduction of surface TiOj molecules on adsorption of reactive metals. Film growth is readily monitored by the disappearance of the XPS signal from the underlying surface [88, 89]. This approach can be applied to polymer surfaces [90] and to determine the thickness of polymer layers on metals [91]. Because it is often used for chemical analysis, the method is sometimes referred to as electron spectroscopy for chemical analysis (ESCA). Since x-rays are very penetrating, a grazing incidence angle is often used to emphasize the contribution from the surface atoms. 

X-ray photoelectron spectroscopy (XPS), also called electron spectroscopy for chemical analysis (ESCA), is described in section Bl.25,2.1. The most connnonly employed x-rays are the Mg Ka (1253.6 eV) and the A1 Ka (1486.6 eV) lines, which are produced from a standard x-ray tube. Peaks are seen in XPS spectra that correspond to the bound core-level electrons in the material. The intensity of each peak is proportional to the abundance of the emitting atoms in the near-surface region, while the precise binding energy of each peak depends on the chemical oxidation state and local enviromnent of the emitting atoms. The Perkin-Elmer XPS handbook contains sample spectra of each element and bindmg energies for certain compounds [58]. 

Other techniques in which incident photons excite the surface to produce detected electrons are also Hsted in Table 1. X-ray photoelectron Spectroscopy (xps), which is also known as electron spectroscopy for chemical analysis (esca), is based on the use of x-rays which stimulate atomic core level electron ejection for elemental composition information. Ultraviolet photoelectron spectroscopy (ups) is similar but uses ultraviolet photons instead of x-rays to probe atomic valence level electrons. Photons are used to stimulate desorption of ions in photon stimulated ion angular distribution (psd). Inverse photoemission (ip) occurs when electrons incident on a surface result in photon emission which is then detected. 

X-rays provide an important suite of methods for nondestmctive quantitative spectrochemical analysis for elements of atomic number Z > 12. Spectroscopy iavolving x-ray absorption and emission (269—273) is discussed hereia. X-ray diffraction and electron spectroscopies such as Auger and electron spectroscopy for chemical analysis (esca) or x-ray photoelectron spectroscopy are discussed elsewhere (see X-raytechnology). 

Lithium foil is commercially available. Its surface is covered with a "native film" consisting of various lithium compounds [Li0H,Li20,Li3N, (Li20-C02) adduct, or Li2C03], These compounds are produced by the reaction of lithium with 02, H20, C02, or N2. These compounds can be detected by electron spectroscopy for chemical analysis (ESCA) [2], As mentioned below, the surface film is closely related to the cycling efficiency. 

Other techniques utilize various types of radiation for the investigation of polymer surfaces (Fig. 2). X-ray photoelectron spectroscopy (XPS) has been known in surface analysis for approximately 23 years and is widely applied for the analysis of the chemical composition of polymer surfaces. It is more commonly referred to as electron spectroscopy for chemical analysis (ESCA) [22]. It is a very widespread technique for surface analysis since a wide range of information can be obtained. The surface is exposed to monochromatic X-rays from e.g. a rotating anode generator or a synchrotron source and the energy spectrum of electrons emitted... 

X-ray scattering studies at a renewed pc-Ag/electrolyte interface366,823 provide evidence for assuming that fast relaxation and diffu-sional processes are probable at a renewed Sn + Pb alloy surface. Investigations by secondary-ion mass spectroscopy (SIMS) of the Pb concentration profile in a thin Sn + Pb alloy surface layer show that the concentration penetration depth in the solid phase is on the order of 0.2 pm, which leads to an estimate of a surface diffusion coefficient for Pb atoms in the Sn + Pb alloy surface layer on the order of 10"13 to lCT12 cm2 s i 820 ( p,emicai analysis by electron spectroscopy for chemical analysis (ESCA) and Auger ofjust-renewed Sn + Pb alloy surfaces in a vacuum confirms that enrichment with Pb of the surface layer is probable.810... 

A relatively new arrangement for the study of the interfacial region is achieved by so-called emersed electrodes. This experimental technique developed by Hansen et al. consists of fully or partially removing the electrode from the solution at a constant electrical potential. This ex situ experiment (Fig. 9), usually called an emersion process, makes possible an analysis of an electrode in an ambient atmosphere or an ultrahigh vacuum (UHV). Research using modem surface analysis such as electron spectroscopy for chemical analysis (ESCA), electroreflectance, as well as surface resistance, electrical current, and in particular Volta potential measurements, have shown that the essential features (e.g., the charge on... 

The effects of tin/palladium ratio, temperatnre, pressnre, and recycling were studied and correlated with catalyst characterization. The catalysts were characterized by chemisorption titrations, in situ X-Ray Diffraction (XRD), and Electron Spectroscopy for Chemical Analysis (ESCA). Chemisorption studies with hydrogen sulfide show lack of adsorption at higher Sn/Pd ratios. Carbon monoxide chemisorption indicates an increase in adsorption with increasing palladium concentration. One form of palladium is transformed to a new phase at 140°C by measurement of in situ variable temperature XRD. ESCA studies of the catalysts show that the presence of tin concentration increases the surface palladium concentration. ESCA data also indicates that recycled catalysts show no palladium sulfide formation at the surface but palladium cyanide is present. 

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. 

Direct measurement of the absolute binding energy and widths of core (X-ray) and valence (UV) bands. The core levels do not participate in bonding, hence each element gives a characteristic XPS spectrum electron spectroscopy for chemical analysis (ESCA). ESCA gives the elemental composition of the surface of a solid sample (except H), the relative amounts of each element present, its oxidation state and some information on the chemical environment around each element. In addition, it is capable of providing an estimate of the depth of a deposited overlaycr... 

The work of Siegbahn s group who, in the 1950s, improved the energy resolution of electron spectrometers and combined it with X-ray sources. This led to a technique called electron spectroscopy for chemical analysis (ESCA), nowadays more commonly referred to as X-ray photoelectron spectroscopy (XPS) [6]. Siegbahn received the Nobel Prize for his work in 1981. Commercial instruments have been available since the early seventies. 

This technique is also known as electron spectroscopy for chemical analysis (ESCA). Although it is concerned with the detection of electrons, it is discussed here because the way in which the photoelectrons are produced is fundamental to the XRF process. As described above, an incident X-ray photon produces an excited ion by ejecting an inner shell electron. The excited... 

As representative techniques of the second group, we discuss two methods x-ray photoelectron spectroscopy (XPS), sometimes referred to as electron spectroscopy for chemical analysis (ESCA) and Auger electron spectroscopy (AES). The main principle of the first method (XPS) is the excitation of electrons in an atom or molecule by x-rays. The resulting electrons carry energy away according to the formula... 

Although not capable of the micrometer-sized lateral resolutions available with the aforementioned techniques, the surface spectroscopy, electron spectroscopy for chemical analysis (ESCA), also deserves mention. The ESCA experiment involves the use of X-rays rather than electrons to eject core electrons (photoelectrons), and it has comparable surface specificity and sensitivity to that of Auger electron spectroscopy (AES) (25, 26, 29). The principal advantage of ESCA relative to AES is that small... 

In spite of these difficulties, the method described is useful in certain special cases. An adaptation of it has been successfully applied to the removal of base-line distortion caused by inelastically scattered electrons in electron spectroscopy for chemical analysis (ESCA) (Chapter 5). As one might suspect, the method is most useful when the end value sL is not small. In the ESCA example, we shall see that when s is written in its continuous formulation s(x), it is actually terminated by a Dirac S function. 

The ten chapters are organized into three main sections. The first four chapters (Jansson) introduce the reader to basic concepts and progress through a survey of both traditional linear and modern nonlinear methods. Chapters 5 (Jansson), 6 (Blass and Halsey), and 7 (Halsey and Blass) detail specific applications of a proven method to the fields of electron spectroscopy for chemical analysis (ESCA) and high-resolution infrared spectroscopy via three different instrumental techniques. Also included are brief examples of applications to nuclear and Raman spectroscopy. The final section, Chapters 8 (Frieden), 9 (Howard), and 10 (Howard), illustrates recent work and reveals some directions for potential future research. 

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