Auger electron spectroscopy bonding

Adhesion and Adhesives Adsorption Auger Electron Spectroscopy Bonding and Structure IN Solids Catalysis, Industrial Catalyst Characterization Chemical Thermodynamics Crystallography Photochemistry, Molecular Photoelectron Spectroscopy Solid-State Electrochemistry Tribology... 

Auger electron spectroscopy (AES) is a technique used to identify the elemental composition, and in many cases, the chemical bonding of the atoms in the surface region of solid samples. It can be combined with ion-beam sputtering to remove material from the surface and to continue to monitor the composition and chemistry of the remaining surface as this surface moves into the sample. It uses an electron beam as a probe of the sample surface and its output is the energy distribution of the secondary electrons released by the probe beam from the sample, although only the Ai er electron component of the secondaries is used in the analysis. 

Surface analysis has made enormous contributions to the field of adhesion science. It enabled investigators to probe fundamental aspects of adhesion such as the composition of anodic oxides on metals, the surface composition of polymers that have been pretreated by etching, the nature of reactions occurring at the interface between a primer and a substrate or between a primer and an adhesive, and the orientation of molecules adsorbed onto substrates. Surface analysis has also enabled adhesion scientists to determine the mechanisms responsible for failure of adhesive bonds, especially after exposure to aggressive environments. The objective of this chapter is to review the principals of surface analysis techniques including attenuated total reflection (ATR) and reflection-absorption (RAIR) infrared spectroscopy. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and secondary ion mass spectrometry (SIMS) and to present examples of the application of each technique to important problems in adhesion science. 

The elemental composition, oxidation state, and coordination environment of species on surfaces can be determined by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) techniques. Both techniques have a penetration depth of 5-20 atomic layers. Especially XPS is commonly used in characterization of electrocatalysts. One common example is the identification and quantification of surface functional groups such as nitrogen species found on carbon-based catalysts.26-29 Secondary Ion Mass spectrometry (SIMS) and Ion Scattering Spectroscopy are alternatives which are more surface sensitive. They can provide information about the surface composition as well as the chemical bonding information from molecular clusters and have been used in characterization of cathode electrodes.30,31 They can also be used for depth profiling purposes. The quantification of the information, however, is rather difficult.32... 

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. 

As demonstrated by the results presented above, the probability of dissociative chemisorption can be readily probed by measuring the extent of carbon deposition by Auger electron spectroscopy. However, a complete picture of the dissociative adsorption process requires that the product of the dissociative chemisorption event be spectroscopically identified. For example, although the discussion has assumed that a single C-H bond cleaves upon dissociation, no evidence for this has been presented. In order to identify chemically the product of the dissociative chemisorption event, we have measured the high resolution electron energy loss spectrum for methane deposited on the Ni(lll) surface at 140 K with an incident energy of 17 kcal/mole. The spectrum is shown in Fig. 4a. A low surface temperature is chosen in order to trap the nascent product of the dissociative chemisorption and not a thermal decomposition product. The temperature of the surface has no effect on the probability for dissociative chemisorption since the dissociation occurs immediately upon impact of the molecule on the surface. 

A silver layer 0.3-1.5 nm thick was deposited on boron-doped diamond and thermally annealed until it disappeared. In contrast to other metals, no evidence for intermixing, graphitization or carbide formation was observed at the interface by Auger electron spectroscopy, ionization loss spectroscopy and low energy electron diffraction263. It was shown by Auger electron spectroscopy that no Ag—Si bonds are formed at the interface of silver deposited on or annealed with silica, in contrast to Ti deposited on or annealed with silica264. 

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