PhysicsLAB Resource Lesson
Famous Experiments: Davisson-Germer

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Three years after de Broglie asserted that particles of matter could possess wavelike properties, the diffraction of electrons from the surface of a solid crystal was experimentally observed by C. J. Davisson and L. H. Germer of the Bell Telephone Laboratory. In 1927 they reported their investigation of the angular distribution of electrons scattered from nickel.  With careful analysis, they showed that the electron beam was scattered by the surface atoms on the nickel at the exact angles predicted for the diffraction of x-rays according to Bragg's formula, with a wavelength given by the de Broglie equation, λ = h / mv.
 
 
Also in 1927, G. P. Thomson, the son of J. J. Thomson, reported his experiments, in which a beam of energetic electrons was diffracted by a thin foil. Thomson found patterns that resembled the x-ray patterns made with powdered (polycrystalline) samples. This kind of diffraction, by many randomly oriented crystalline grains, produces rings. If the wavelength of the electrons is changed by changing their incident energy, the diameters of the diffraction rings change proportionally, as expected from Bragg's equation.
 
 
Adobe Illustrator images provided courtesy of J. Burch, 2002

The diffraction patterns simulated above compare the effects of x-rays passing through a thin foil with those of high energy electrons passing through the same medium. Notice how similar the patterns are to each other when the de Broglie wavelength of an electron beam equals the wavelength of the original x-rays. A similar set of images can be viewed at Hackensack High School.
 
These experiments by Davisson and Germer and by Thomson proved that de Broglie's waves are not simply mathematical conveniences, but have observable physical effects. The 1937 Nobel Prize in Physics was awarded to these gentlemen for their pioneering work. Just as Compton showed that waves could act like particles, Davisson and Germer showed that particles could act as waves.



 
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