Davisson–Germer experiment
This confirmed the hypothesis, advanced by Louis de Broglie in 1924, of wave-particle duality, and also the wave mechanics approach of the Schrödinger equation.
However, this was challenged in Albert Einstein's 1905 paper on the photoelectric effect, which described light as discrete and localized quanta of energy (now called photons), which won him the Nobel Prize in Physics in 1921.
[4][5] This suggestion of Elsasser was then communicated by his senior colleague (and later Nobel Prize recipient) Max Born to physicists in England.
However the initial intention of the Davisson and Germer experiment was not to confirm the de Broglie hypothesis, but rather to study the surface of nickel.
In 1927 at Bell Labs, Clinton Davisson and Lester Germer fired slow moving electrons at a crystalline nickel target.
The angular dependence of the reflected electron intensity was measured[1][2] and was determined to have a similar diffraction pattern as those predicted by Bragg for X-rays; some small, but significant differences[3] were due to the average potential which Hans Bethe showed in his more complete analysis.
To remove the oxide, Davisson and Germer heated the specimen in a high temperature oven, not knowing that this caused the formerly polycrystalline structure of the nickel to form large single crystal areas with crystal planes continuous over the width of the electron beam.
This, in 1925, generated a diffraction pattern with unexpected and uncorrelated peaks due to the heating causing a ten crystal faceted area.
[13] Davisson then learned that in prior years, other scientists – Walter Elsasser, E. G. Dymond, and Blackett, James Chadwick, and Charles Ellis – had attempted similar diffraction experiments, but were unable to generate low enough vacuums or detect the low-intensity beams needed.
[13] Returning to the United States, Davisson made modifications to the tube design and detector mounting, adding azimuth in addition to colatitude.
[1] Questions still needed to be answered and experimentation continued through 1927, because Davisson was now familiar with the de Broglie formula and had designed the test to see if any effect could be discerned for a changed electron wavelength
Because of their failure to correlate with the de Broglie formula, their paper introduced an ad hoc contraction factor of 0.7, which, however, could only explain eight of the thirteen beams.
The highest intensity was observed at an angle θ = 50° with a voltage of 54 V, giving the electrons a kinetic energy of 54 eV.
[4] As Max von Laue proved in 1912, the periodic crystal structure serves as a type of three-dimensional diffraction grating.
"[3] So although electron energy diffraction does not follow the Bragg law, it did confirm de Broglie's theory that particles behave like waves.
The full explanation was provided by Hans Bethe who solved Schrödinger equation[15] for the case of electron diffraction.
[6] Davisson and Germer's accidental discovery of the diffraction of electrons was the first direct evidence confirming de Broglie's hypothesis that particles can have wave properties as well.
Davisson's attention to detail, his resources for conducting basic research, the expertise of colleagues, and luck all contributed to the experimental success.
It wasn't until much later that development of experimental methods exploiting ultra-high vacuum technologies (e.g. the approach described by Alpert in 1953[16]) enabled the extensive use of LEED diffraction to explore the surfaces of crystallized elements and the spacing between atoms.
