ESCA/XPS

Surface characterization regarding other electron spectroscopies. To evidence specific attributes of HREELS to be compared to ESCA (XPS), UPS or AES ones, we chose to present (Figure 3) spectra recorded from polystyrenes (2). These thin film samples were made from normal and fully deuterated polymers. Immediately, it appears that HREELS is really capable of adding a new and unique dimension to electron surface analyses as ... 

ESCA, XPS Electron spectroscopy for chemical analysis, X-ray photoelectron spectroscopy X-rays Electrons... 

A commercial ESCA/XPS instrument consists of four major components housed in a UHV system with magnetic shielding (1) the radiation source, consisting of an X-ray source and a means of providing highly monochromatic X-rays (2) the sample holder ... 

A sample of pure lead was evaporated onto a surface, which was then exposed to air. The ESC A spectra were obtained at various time intervals as indicated in Fig. 14.19. The spectra show the formation of lead oxide on the surface, going through the intermediate of PbO and finally, after a number of hours, to Pb02. This demonstrates the capability of ESCA/XPS to study surface chemistry. 

Surface segregation is normally studied experimentally by the surface-sensitive techniques of photoelectron spectroscopy (ESCA, XPS), Auger electron spectroscopy and atom probe. 

Figure 14.19 The use of ESCA (XPS) to study changes in the surface composition of Pb on exposure to air and heat. (Reprinted from Endeavor, 32, Siegbahn, K., 51, Copyright 1973. With permission from Elsevier.)...

Aschematical drawing of the transitions involved in ESCA/XPS and AES is given in figure IV - 46. XPS or ESCA are two names for one and the same technique, with excitation occurring by means of photons (hv) and with photoelectrons constituting the... 

Figure IV 46. Schematic drawing of the electron transitions involved in ESCA/XPS and AES measurements.

ESCA/XPS methods can detect atoms to a depth of 0.5 - 10 nm which makes this technique most useful for the detemiination of surface stmctures. 

ESCA (XPS) studies have been carried out on several metals, and in all cases the metal has been shown to be in the zerovalent state. Bulk analysis also clearly shows that the metal powders are complex materials containing in many cases... 

Also known as electron spectroscopy for chemical analysis (ESCA), XPS utilizes x-rays and photoelectric phenomena to study electronic structure, compound composition, electron and chemical states, electron bonding, and surface analysis [34-36]. In practice, a sample is bombarded by a monochromatic single wavelength x-ray beam. This causes core electrons from the sample to overcome their binding energy and escape to the sample surface where they are detected [34]. 

Among all the methods of ESCA, XPS has been found to show the greatest applicability. It has been widely used for the surface characterization of materials, especially catalysts. As addressed above, XPS analysis can give sufficient information about the qualitative and quantitative elemental surface composition of a catalyst, the oxidation state of an atom, the chemical environment, and so forth. The following paragraphs give some typical analysis examples of XPS for fuel cell catalysts. 

ESCA/XPS Atoms at surface How they are bonded Paints, paper surfaces, polymers, pigments, minerals, metals... 

Abbreviations ESCA/XPS = electron spectroscopy for chemical analysis (X-ray photoelectron spectroscopy) NMR = nuclear magnetic resonance FT-IR = Fourier-transformed-infrared radiation. Fourier transformation is an algorithm used to treat signals. 

Table 17.15 shows results obtained from the application of various bulk and surface analysis methods to lithium metal at rest or after cyclization experiments, as well as at noble metal and carbon electrodes after cathodic polarization. Several surface and elemental analysis methods are applied, including X-ray photoelectron spectroscopy (XPS, ESCA/XPS), energy dispersive analysis of X-rays (X-ray microanalysis, EDAX), Eourier transform infrared spectroscopy (ETIR), Auger electron spectroscopy (AES), ellipsometry (E), electro-modulated infrared reflectance spectroscopy (EMIRS), double modulation Fourier transform infrared spectroscopy (DMFTIR), subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS), gas chromatography (GC), IR spectroscopy. X-ray diffraction (XRD), and atomic force microscopy (AFM). 

This technique in trained hands yields more information about a material than aity other single microanalytical tool. Since the 1970s, however, techniques and instrumentation which can aid the analyst whose material problems may lie beyond the capabilities of the hght microscope have been developed TEM, SEM, ESCA/XPS, and Auger, among others, are the new accessories to which the chemist in search of answers to microscopical problems can also turn. 

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