Quantitative Auger electron spectroscopy

Quantitative Auger electron spectroscopy depth profiling of iron oxides formed on Fe (100) and polycrystalline Fe by exposure to gas phase oxygen and borate buffer solution. Langmuir 6 1683-1690... 

The present paper reviews the physical and chemical evidence for the above rules obtained over the last several years from ultrahigh vacuum surface science studies of molybdenum single crystals chemically modified by 0, C, S, and B. Additionally, the results of recent studies of methylcyclopropane hydrogenolysis will be presented which illustrate the influence of surface acid/base sites on catalytic hydrocarbon conversions. The surface coverage of each modifier was determined by quantitative Auger electron spectroscopy or x-ray photoelectron spectroscopy (XPS). The atomic structure of oxygen, carbon, and sulfur adlayers below one monolayer (ML)... 

In other articles in this section, a method of analysis is described called Secondary Ion Mass Spectrometry (SIMS), in which material is sputtered from a surface using an ion beam and the minor components that are ejected as positive or negative ions are analyzed by a mass spectrometer. Over the past few years, methods that post-ion-ize the major neutral components ejected from surfaces under ion-beam or laser bombardment have been introduced because of the improved quantitative aspects obtainable by analyzing the major ejected channel. These techniques include SALI, Sputter-Initiated Resonance Ionization Spectroscopy (SIRIS), and Sputtered Neutral Mass Spectrometry (SNMS) or electron-gas post-ionization. Post-ionization techniques for surface analysis have received widespread interest because of their increased sensitivity, compared to more traditional surface analysis techniques, such as X-Ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES), and their more reliable quantitation, compared to SIMS. 

This kind of estimation of the relative concentration is the most widely used method for quantitative EELS analysis. It is advantageous because the dependence on the primary electron current, Iq, is cancelled out this is not easily determined in a transmission electron microscope under suitable analytical conditions. Eurthermore, in comparison with other methods, e. g. Auger electron spectroscopy and energy-disper-... 

There is now available a substantial amount of information on the principles and techniques involved in preparing evaporated alloy films suitable for adsorption or catalytic work, although some preparative methods, e.g., vapor quenching, used in other research fields have not yet been adopted. Alloy films have been characterized with respect to bulk properties, e.g., uniformity of composition, phase separation, crystallite orientation, and surface areas have been measured. Direct quantitative measurements of surface composition have not been made on alloy films prepared for catalytic studies, but techniques, e.g., Auger electron spectroscopy, are available. 

Auger electron spectroscopy (AES), 76 495 24 84-87, 94-97. See also AES instrumentation archaeological materials, 5 744 quantitative, 24 98 Auger sensitivity factors, 24 96 Auger spectra, 24 95-97, 98 Auger transitions, 24 95 Augite, in coal, 6 718 Au(III) halides, 72 706. See also Gold(III) entries... 

Over the past 10 years a multitude of new techniques has been developed to permit characterization of catalyst surfaces on the atomic scale. Low-energy electron diffraction (LEED) can determine the atomic surface structure of the topmost layer of the clean catalyst or of the adsorbed intermediate (7). Auger electron spectroscopy (2) (AES) and other electron spectroscopy techniques (X-ray photoelectron, ultraviolet photoelectron, electron loss spectroscopies, etc.) can be used to determine the chemical composition of the surface with the sensitivity of 1% of a monolayer (approximately 1013 atoms/cm2). In addition to qualitative and quantitative chemical analysis of the surface layer, electron spectroscopy can also be utilized to determine the valency of surface atoms and the nature of the surface chemical bond. These are static techniques, but by using a suitable apparatus, which will be described later, one can monitor the atomic structure and composition during catalytic reactions at low pressures (< 10-4 Torr). As a result, we can determine reaction rates and product distributions in catalytic surface reactions as a function of surface structure and surface chemical composition. These relations permit the exploration of the mechanistic details of catalysis on the molecular level to optimize catalyst preparation and to build new catalyst systems by employing the knowledge gained. 

Recent developments in the use of Auger electron spectroscopy (AES) have improved the possibilities for a quantitative study of the surface composition (lOa-IOd). By employing an internal standard (77) many of the ambiguities of previous applications have been eliminated. The application of AES has greatly improved the reliability of surface composition determinations compared with previous results. 

As a surface analytical tool, SIMS has several advantages over X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). SIMS is sensitive to all elements and isotopes in the periodic table, whereas XPS and AES cannot detect H and He. SIMS also has a lower detection limit of 10 5 atomic percent (at.S) compared to 0.1 at.S and 1.0 at.% for AES and XPS, respectively. However, SIMS has several disadvantages. Its elemental sensitivity varies over five orders of magnitude and differs for a given element in different sample matrices, i.e., SIMS shows a strong matrix effect. This matrix effect makes SIMS measurements difficult to quantify. Recent progress, however, has been made especially in the development of quantitative models for the analysis of semiconductors [3-5]. 

XPS and to a lesser extent, Auger electron spectroscopy (AES) have been applied to detect the presence of and to determine the extent of surface modification. Most of these qualitative and semi-quantitative studies have monitored certain elements which occurred in the mediator and not on the unmodified surface. The sustained presence of such element(s) following... 

Some of the most recognized tests to detect, measure, and quantitate the chrome/iron ratio and to ensure that a passive layer has been established are the Ferroxyl Test for Free Iron, X-Ray Photoelectron Spectroscopy (XPS) or Electron Spectroscopy for Chemical Analysis (ESCA), and Auger Electron Spectroscopy (AES). 

Powell, C. J., and Seah, M. P., Precision, accuracy, and uncertainty in quantitative surface analyses by Auger-electron spectroscopy and x-ray photoelectron spectroscopy, J. Vac. Sci. Technol., A8(2), 735 (1990). 

Electron, ion, and photon emissions from the outermost layers of the particle surface can be used to reveal the qualitative or quantitative information on chemical composition of the surface of ceramic powders. The most widely used techniques include (i) Auger electron spectroscopy (AES), (ii) X-ray photoelectron spectroscopy (XPS), which is also known as electron spectroscopy for chemical analysis (ESCA), and (iii) Secondary ion mass spectrometry (SIMS). 

The analysis of metals by X-ray fluorescence has been widely used on geological and sediment samples, either deposited on filters or as thin films. The method can be made quantitative by using geological standards and transition metals can be determined in the 1-5 tg per g range. The surfaces of sediment particles can be examined by the direct use of electron microprobe X-ray emission spectrometry and Auger electron spectroscopy. Although these methods are not particularly sensitive, they can allow the determination of a depth-profile of trace metals within a sediment particle. 

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