Davisson-Germer electron diffraction

Davisson/Germer electron diffraction by metal crystal... 

Davisson/Germer Electron beam is diffracted by metal crystal. 

The wavelike character of electrons was detected by showing that they could be diffracted. The experiment was first performed in 1925 by two American scientists, Clinton Davisson and Lester Germer, who directed a beam of fast electrons at a single crystal of nickel. The regular array of atoms in the crystal, with centers separated by 250 pm, acts as a grid that diffracts waves and a diffraction pattern was observed (Fig. 1.10). Electron diffraction is now an important technique for determining the structures of molecules and exploring the structures of solid surfaces. 

Louis de Broglie discussed the relations between energy, momentum, and wavelength for photons as well as for electrons and examined the results of the Davisson-Germer experiment on the diffraction of electrons by crystals, which were in perfect agreement with theory. 

The matter field was originally postulated by Louis de Broglie, and discovered in the electron diffraction studies of Davisson and Germer [30] and of G. P. Thomson [31]. From Schrodinger s understanding of the matter field of, say, an electron, it must be represented in the source terms (charge and current density) of Maxwell s equations, as the moduli of these waves. 

Clinton Davisson and Lester Germer demonstrate electron diffraction at the Bell Laboratories in New Jersey. 

Demonstrating electron diffraction (a property associated with waves) was proof of their wave nature. In 1927 C.J. Davisson and L. Germer in the United States and, independently, G.P. Thomson and A. Reid in the United Kingdom showed that electrons could be diffracted in much the same way as X-rays. We care because we cannot explain the properties of electrons and X-rays without this understanding. 

Davisson, Clinton Davis and Germer, Lester Halbert were working at Bell Labs at the time of their discovery of electron diffraction. Davisson died in 1958 at age 76 (born 1881) and Germer died in 1971 at age 75 (born 1896). 

In 1927, Davisson and Germer demonstrated that electrons are diffracted by crystals in a manner similar to the diffraction of X rays. These electron-diffraction experiments substantiated de Broglie s suggestion that an electron has wave properties such as wavelength, frequency, phase, and interference. In seemingly direct contradiction, however, certain other experiments, particularly those of J. J. Thomson, showed that an electron is a particle with mass, energy, and momentum. 

Introduction.— The theory necessary to carry out a fairly accurate electron-diffraction investigation was developed many years ago. The bases of the theory are to be found in papers by Rutherford, Debye, and Ehrenfest. Thus most of the theory was available when Davisson and Germer and Thomson made their famous experiments on the diffraction of electrons by crystals and so verified de Broglie s relation, and when Mark and Wierl carried out the first experiments on scattering of electrons by gases. An important contribution to the theory was also made by Fax n and Holtsmark in 1927, but their results were not applied to structure determinations by gas electron diffraction until about two decades ago. ... 

Figure 12.9 Davisson and Germer s apparatus and electron diffraction pattern... 

De Brc lie proposed that matter should show wave-like properties. The de Broglie hypothesis was supported by Davisson and Germer s studies of electron diffraction. Every object has a wavelength that depends on its momentum (the product of its mass and velocity). 

Low energy electron diffraction (LEED) is the extension of Clinton Davisson and Lester Germer s 1927 experiment at Bell Labs into a practical tool for characterizing the surfaces of clean solids. The experiments agreed so convincingly with de Broglie s predictions of a few years earlier that particles and waves could never again be completely separated in the minds of physicists. 

Fii 9.6 In the Davisson-Germer experiment, a beam of electrons was directed on a single crystal of nickel, and the scattered electrons showed a variation in intensity with angle that corresponded to the pattern that would be expected if the electrons had a wave character and were diffracted by the layers of atoms in the solid. 

It is now 32 years since Davisson and Germer did their first experiment on the diffraction of electrons and thus gave the proof for the validity of the de Broglie relation. Since then the electron diffraction method has been open for the study of the structure of matter, and a large number of problems have been treated with this method, using both the diffraction from solid material and from gases. 

In 1927, a key experiment by Davisson and Germer at BeU Laboratories in the United States showed that a beam of electrons (particles) were diffracted from an annealed crystal lattice of Ni atoms. The property of diffraction is a key characteristic of waves. This set the stage to use wave mechanics to describe phenomena at the small scale of atoms and molecules. In addition, a new technique of low-energy electron diffraction (LEED) was developed to study material surfaces at the atomic level. 

Criterion 3 Importance of Davisson-Germer Experiments and Their Struggle to Interpret Experimental Data. Of the 128 textbooks analyzed none described Satisfactorily (S) the difficulties involved in interpreting the Davisson-Germer experiments as evidence for the wave nature of the electron (see Table 2). Only one textbook came close to describing the unexpected diffraction patterns in the following terms and was classified as Mention (M) ... 

A sample of nickel [in Davisson-Germer experiments] was accidentally converted into crystalline form and, when subjected to the electron beam, produced totally unexpected diffraction patterns. .. similar to those observed in X-ray diffraction by crystals. .. Such behavior indicated that electrons, like electromagnetic radiation, possess wave characteristics (O Connor 1974, p. 50). 

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