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Angle-Resolved Auger Electron Spectroscopy
Published in Arthur T. Hubbard, The Handbook of Surface Imaging and Visualization, 2022
The propagation of elastically scattered Auger electrons near the surface of a solid has received substantial attention historically due to the widespread popularity of low-energy electron diffraction (LEED).41 In most cases, however, the formalisms developed for LEED interpretation are not directly applicable to the Auger experiment. In the LEED experiment, a collimated incident beam of electrons (plane wave) is directed toward a surface, and the angular distribution of elastically reflected electrons is measured. Emphasis is placed upon those electrons that are diffracted in collimated beams (plane waves). In contrast, Auger electrons are emitted incoherently from atoms near the surface essentially as spherical waves, which are then scattered by other atoms in the surface region. Accordingly, new theoretical approaches are required to account for the experimental observations. Several models have been proposed,10,17,30,31,35—37 with limited success. The most widely used formalisms can be divided into two categories: “forward scattering” and “holography.”
Preparation of Thin Oxide Films: Concepts and Toolkits
Published in Shamil Shaikhutdinov, Introduction to Ultrathin Silica Films Silicatene and Others, 2022
LEED is one of the mostly used techniques for studying crystalline and well-ordered surfaces and interfaces. The principles of electron diffraction are intimately connected to the wave-like nature of elementary particles, first introduced by Louis de Broglie in 1924 and then confirmed experimentally by Davisson and Germer in 1927. However, LEED only became an experimental tool in the 1960s thanks to substantial progress in electron detection methods and development of vacuum systems capable to prepare clean surfaces. In LEED, the incident e-beam is considered as a plane wave with a wavelength depending on the electron energy through the de Broglie wave equation. Accordingly, the 100 eV electrons have the de Broglie wavelength about 1 Å, i.e., comparable with interatomic distances in solids. The method is particularly surface sensitive because of using electron energies close to the minimum in the escape depth (see Fig. 2.1). As all diffraction-based techniques, LEED requires long-range ordering at surface, at least the presence of ordered domains larger than the coherence length of the probing electrons, in the range of 5–10 nm, in order to be detected with conventional apparatus.
In, Out, Shake It All About
Published in Sharon Ann Holgate, Understanding Solid State Physics, 2021
Low-energy electron diffraction (LEED) is used to study the positions of atoms in the surface layers of solids. These positions are usually different to those within the bulk of the solid. LEED involves directing a beam of electrons with energies between ≈20 and ≈250 eV at the sample, and recording the resulting diffraction pattern on a fluorescent screen placed on the same side of the sample as the “electron gun” that produces the beam of electrons. It is only electrons diffracted from the first three or four layers of atoms that make it back out of the sample, so the pattern will only represent the atomic structure of the surface. This experimental arrangement enabled Davisson and Germer to discover the wavelike nature of electrons back in 1927. (See Section D1 of Appendix D for more about their experiment.)
New perspectives on the nature and imaging of active site in small metallic particles: II. Electronic effects
Published in Chemical Engineering Communications, 2021
Low energy electron diffraction (LEED) has also been extensively used in the analysis of surface structures of chemisorbed layers of small molecules such as CO, O2, H2, H2O, etc. on low-index planes, (111) and (100), of Pt. It is also important to note that there are striking differences in the surface structures of low-index planes and high-index planes, such as (110) or (211). The high-index planes are characterized by the presence of flat terraces – of several atomic widths in size — linked by steps, usually of monoatomic height. The LEED analysis of surface structures on high-index planes is important because the surface structures of adsorbates is different on these planes (compared to low-index ones). These adsorbates are more likely to be present as intermediates in elementary steps of surface reactions, and it is therefore important to identify the surface structures of these “transition-state” type intermediates. Also, these high-index planes are more prevalent in catalytic nanoclusters, or nanoparticles of a certain particle size/grain size; the technical catalysts important from the standpoint of catalytic transformations of significance from scientific and industrial standpoint.