![]() Notably, future Nobel prize winner Gerhard Ertl started his studies of surface chemistry and catalysis on such a Varian system. In the mid-1960s, modern LEED systems became commercially available as part of the ultra-high-vacuum instrumentation suite by Varian Associates and triggered an enormous boost of activities in surface science. In 1962 Lander and colleagues introduced the modern hemispherical screen with associated hemispherical grids. Ironically the post-acceleration method had already been proposed by Ehrenberg in 1934. Using this technique, diffracted electrons were accelerated to high energies to produce clear and visible diffraction patterns on the screen. In the early 1960s LEED experienced a renaissance, as ultra-high vacuum became widely available, and the post acceleration detection method was introduced by Germer and his coworkers at Bell Labs using a flat phosphor screen. Farnsworth and coworkers at Brown University pioneered the use of LEED as a method for characterizing the absorption of gases onto clean metal surfaces and the associated regular adsorption phases, starting shortly after the Davisson and Germer discovery into the 1970s. Techniques for the preparation of clean metal surfaces first became available much later. ![]() Also, since LEED is a surface-sensitive method, it required well-ordered surface structures. The main reasons were that monitoring directions and intensities of diffracted beams was a difficult experimental process due to inadequate vacuum techniques and slow detection methods such as a Faraday cup. Though discovered in 1927, low-energy electron diffraction did not become a popular tool for surface analysis until the early 1960s. Those experiments revealed the wave property of electrons and opened up an era of electron-diffraction study.ĭevelopment of LEED as a tool in surface science One month after Davisson and Germer's work appeared, Thompson and Reid published their electron-diffraction work with higher kinetic energy (thousand times higher than the energy used by Davisson and Germer) in the same journal. Before the acceptance of the de Broglie hypothesis, diffraction was believed to be an exclusive property of waves.ĭavisson and Germer published notes of their electron-diffraction experiment result in Nature and in Physical Review in 1927. These observations were consistent with the diffraction theory for X-rays developed by Bragg and Laue earlier. The de Broglie hypothesis was confirmed experimentally at Bell Labs in 1927, when Clinton Davisson and Lester Germer fired low-energy electrons at a crystalline nickel target and observed that the angular dependence of the intensity of backscattered electrons showed diffraction patterns. In his Nobel-laureated work de Broglie postulated that the wavelength of a particle with linear momentum p is given by h/ p, where h is Planck's constant. The theoretical possibility of the occurrence of electron diffraction first emerged in 1924, when Louis de Broglie introduced wave mechanics and proposed the wavelike nature of all particles. Davisson and Germer's discovery of electron diffraction By comparison with theoretical curves, these may provide accurate information on atomic positions on the surface at hand.Īn electron-diffraction experiment similar to modern LEED was the first to observe the wavelike properties of electrons, but LEED was established as an ubiquitous tool in surface science only with the advances in vacuum generation and electron detection techniques. Quantitatively, where the intensities of diffracted beams are recorded as a function of incident electron beam energy to generate the so-called I–V curves.In the presence of an adsorbate the qualitative analysis may reveal information about the size and rotational alignment of the adsorbate unit cell with respect to the substrate unit cell. Qualitatively, where the diffraction pattern is recorded and analysis of the spot positions gives information on the symmetry of the surface structure.Low-energy electron diffraction ( LEED) is a technique for the determination of the surface structure of single-crystalline materials by bombardment with a collimated beam of low-energy electrons (30–200 eV) and observation of diffracted electrons as spots on a fluorescent screen. Also seen is the electron gun that generates the primary electron beam it covers up parts of the screen. The diffraction spots are generated by acceleration of elastically scattered electrons onto a hemispherical fluorescent screen. As discussed in the text, the pattern shows that reconstruction exists in symmetrically equivalent domains oriented along different crystallographic axes. The underlying lattice is a square lattice, while the surface reconstruction has a 2×1 periodicity. Technique for the determination of the surface structure of single-crystalline materials Figure 1: LEED pattern of a Si(100) reconstructed surface.
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