Interfaces Auger electron spectroscopy

Auger electron spectroscopy is the most frequently used surface, thin-film, or interface compositional analysis technique. This is because of its very versatile combination of attributes. It has surface specificity—a sampling depth that varies... 

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. 

Fig. 12. Auger electron spectroscopy (AES) sputter-depth profile of CAA-treated titanium after various exposure.s in vacuum (a) as anodized, (b) 450°C for 1 h, and (c) 7(X)°C for 1 h. The sputter etch rate is 1.5 nm/min. The line indicates the original interface. The arrow denotes oxygen diffused into the substrate. Adapted from Ref. [51].

As mentioned previously, this can be attributed in part to the lack of structure-sensitive techniques that can operate in the presence of a condensed phase. Ultrahigh-vacuum (UHV) surface spectroscopic techniques such as low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and others have been applied to the study of electrochemical interfaces, and a wealth of information has emerged from these ex situ studies on well-defined electrode surfaces.15"17 However, the fact that these techniques require the use of UHV precludes their use for in situ studies of the electrode/solution interface. In addition, transfer of the electrode from the electrolytic medium into UHV introduces the very serious question of whether the nature of the surface examined ex situ has the same structure as the surface in contact with the electrolyte and under potential control. Furthermore, any information on the solution side of the interface is, of necessity, lost. 

The most popular of these are secondary ion mass spectroscopy (SIMS), ion scattering spectroscopy (ISS), and Auger electron spectroscopy (AES) which have been developed by investigators such as Baun, McDevitt, and Solomon.16-20 These tools have proved practical even when the surface films are only on the order of atomic dimensions or when the failure occurred near the original interface and included parts of both the adhesive and the adherend. 

Books. M. W. Roberts, Chemistry of the Metal-Gas Interface , Oxford University Press, Oxford, 1978 F. C. Tompkins, Chemisorption of Gases on Metals , Academic Press, London, 1978 Experimental Methods in Catalysis Research , ed. R. B. Anderson and P. T. Dawson, Academic Press, London, 1976 Chemistry and Physics of Solid Surfaces , ed. R. Vanselow and S. Y. Yong, CRC Press, Cleveland, Ohio, 1977 Advances in Characterisation of Metal and Polymer Surfaces , ed. L. H. Lee, Academic Press, New York, 1976 K. Tamaru, Dynamic Heterogeneous Catalysis , Academic Press, London, 1978 The Solid-Vacuum Interface , ed. A. van Oostrom and M. J. Sparnay, Surface Sci., 1977, 64 Electron Spectroscopy , ed. C. R. Brundle and A. D. Baker, Academic Press, New York, 1977, Vol. 1 Auger Electron Spectroscopy (Bibliography 1925—1975) , compiled by D. T. Hawkins, Plenum, New York, 1977. 

The relevance of Auger electron spectroscopy to the solution of various theoretical and practical problems arising from the presence of sulfur at metallic surfaces and interfaces is discussed the relations between phenomenological data such as reaction rates or activation energies and surface characterization with respect to the crystallographic structure and the composition of the surface are reviewed and commented upon. 

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. 

The composition of wet thermal oxide on SiC has been established to be close to stoichiometric Si02 from Auger electron spectroscopy sputter depth profiles and from the refractive index of the oxide determined by ellipsometry [4,12,14,19,21,24-27]. Dry oxide on 3C-SiC has been found to contain much more silicon than stoichiometric Si02 [27]. The carbon content of the SiC thermal oxide layer, away from the interface, determined by Auger spectroscopy, has been reported as at below detection limits for wet oxide on 6H-SiC [25] at below detection limits [24,26] and also at 2% for dry oxide on 3C-SiC [27] and at 14% for wet oxide on 3C-SiC [27]. The oxide on SiC grown below 1200°C is amorphous, but above 1200°C the oxide grown is increasingly crystalline [15,18,20,22-24,28]. 

Wang, P. S., Malghan, S. G., Hsu, S. M., and Wittberg, T. N., Surface oxidation of silicon carbide platelets as studied by x-ray photoelectron spectroscopy and bremsstrahlung-excited Auger electron spectroscopy. Surf. Interfac. Anal., 18, 159 (1992). 

The reducticxi of the process tenperature results in very little reaction between the film and the substrate as shown by the Auger electron spectroscopy (AES) results of figs. 9a and 9b. In fig. 9a the AES results Indicate a reacted layer on the order of 100 ntn in a HTP film of the order of 350 nm. However, in the LTP film shown in fig. 9b the interface reacticxi extends over a region of less than 12 nm, close to the Instrument resolution of the technique. This result is very important for the fabrication of structures containing abn rt junction. 

In electrochemistry, because electrical quantities are easy to use and provide information directly relating to the behavior of the interface, they are particularly useful to identify interfacial processes. Contrary to other techniques, which require a vacuum chamber [low-energy electron diffraction (LEED), Auger electron spectroscopy, etc.] or electromagnetic radiation (optical ellipsometry, or X-rays EXAFS), which need no alteration of the electrode surface, electrical techniques can be used in situ on any surface state of the electrode. In addition, thanks to the advances in electronics, experimentalists can use more and more sophisticated... 

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