Surface-structure analysis by forward scattering in photoelectron and Auger-electron diffraction and by backscattered primary electron diffraction
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Low-energy electron diffraction
Auger electron spectroscopy
Gas electron diffraction
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Auger effect
The characteristics of an Auger–low energy electron diffraction (LEED) system constructed with two grids have been studied. The modulation signal is fed to the sample, while the retarding field is applied to the collector instead of the grids; thus the energy analysis is made at the collector. The results show that (i) the system can give the Auger, elastic, and loss signals separately, (ii) the energy resolution for the Auger signal is almost constant (0.6 eV) and much better than that of the cylindrical mirror analyzer (CMA), and (iii) the LEED system shows high contrast compared with the typical four-grid configuration.
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We show that, for certain experimental geometries, the angular dependence of medium-energy backscattered primary electrons from Ni(001) and pseudomorphic Cu on Ni(001) is very similar to that observed in high-energy LMM Auger emission. Both experiments reveal strong forward-scattering induced maxima along low-index directions which are sensitive to the tetragonal distortion accompanying pseudomorphism. The measured displacement of the diffraction feature along [011] in polar-angle scans is the same within experimental error in both measurements. Comparison with theoretical angular distributions obtained by kinematical scattering theory indicates an overlayer lattice constant perpendicular to the interface of 3.75\ifmmode\pm\else\textpm\fi{}0.02 A\r{}, in excellent agreement with the value obtained by Auger electron diffraction (3.71\ifmmode\pm\else\textpm\fi{}0.03 A\r{}). Significantly, medium-energy backscattered electron diffraction should prove to be a powerful tool for overlayer structural characterization because the technique is not limited to elements which emit a high-energy Auger electron of sufficient intensity to be useful as a diffraction probe.
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This chapter contains sections titled: Overview Scattering Cross Section Electron Beam Spectroscopies Auger Electron Spectroscopy Auger Depth Profiling Summary
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This book presumes that the reader is interested in experimental techniques for examining surface and thin film processes; however, there are many books devoted to surface physics and chemistry techniques, some of which are given as further reading at the end of the chapter. There are even several books which are just about one technique, such as Pendry (1974) or Clarke (1985), both on low energy electron diffraction (LEED) in relation to surface crystallography. By the mid-1980s it was already stretching the limits of the review article format to compare the capabilities of the available surface and thin film techniques (Werner & Garten 1984).
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The surface structure of diamond is determined by comparing angle-resolved Auger-electron spectroscopy data to a theoretical model of electron diffraction in a cluster. The diffraction pattern of carbon KVV Auger-electron emission at 265 eV from a diamond(100) surface was obtained in an ultrahigh vacuum chamber. The polar scan curves of the experimental data at azimuthal angles 0\ifmmode^\circ\else\textdegree\fi{}, 15\ifmmode^\circ\else\textdegree\fi{}, 30\ifmmode^\circ\else\textdegree\fi{}, and 45\ifmmode^\circ\else\textdegree\fi{} are compared to theoretical predictions obtained using a single scattering cluster model. The calculated polar intensity distributions are a fairly sensitive function of surface structure. Optimal agreement with experiment occurs when there is a (2\ifmmode\times\else\texttimes\fi{}1) reconstruction at the diamond surface and there is a perpendicular expansion of 0.015(\ifmmode\pm\else\textpm\fi{}0.001) \AA{} between layers 1 and 2, 0.010(\ifmmode\pm\else\textpm\fi{}0.003) \AA{} between layers 2 and 3 and 0.005(\ifmmode\pm\else\textpm\fi{}0.005) \AA{} between layers 3 and 4. \textcopyright{} 1996 The American Physical Society.
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Abstract Auger electron spectroscopy (AES) is a method for determining the elemental composition of the several outermost atomic layers of materials. The surface layers often have a composition that is quite different from the bulk material due to contamination, oxidation, or processing. In AES, a specimen is probed with an energetic electron beam with an energy fixed between 3 and 30 keV, resulting in the ejection of core‐level electrons from atoms. The resulting vacancy in a core level can be filled by an outer‐level electron, with the excess energy being used to emit either an x‐ray (electron probe microanalysis) or another electron from the atom (AES). This emitted electron is called an Auger electron. AES is a surface‐sensitive technique due to the strong inelastic scattering of low‐energy electrons traveling within specimens. Auger electrons from only the outermost several atomic layers are emitted from the specimen without energy loss, and contribute to the Auger peak intensities in a spectrum. The Auger electron kinetic energies are characteristic of the emitting atoms, and the measurement of their energies is used to identify the elements that produce them. The concentrations of elements detected can be determined from the intensities of the Auger peaks. Variation of composition with depth can be determined by depth profiling, which is usually accomplished by removing atomic layers by sputtering with inert gas ions and monitoring the Auger signals from the newly created surfaces. For most elements, the detection limit with AES is between 0.1 and 1 at.%.
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