Davisson and Germer Experiment

The Davisson and Germer Experiment established the wave nature of electrons and confirmed the de Broglie equation for the first time. De Broglie proposed the dual nature of matter in 1924, but Davisson and Germer later validated the findings. For the first time in an experiment, the data demonstrated quantum mechanics. In this experiment, we’ll look at the scattering of electrons by a Ni crystal. Let’s take a closer look.

A vacuum chamber is used for the Davisson and Germer experiment. As a result, electron deflection and scattering by the medium are avoided.

Davisson and Germer Experiment

The Davisson-Germer experiment revealed the electron’s wave character, validating deBroglie’s earlier hypothesis. It was a big step forward in the development of quantum mechanics because it put wave-particle duality on a firm experimental footing. The Bragg diffraction law had previously been applied to x-ray diffraction, but this was the first time it had been applied to particle waves.

Davisson and Germer conceived and built a vacuum apparatus for determining the energy of dispersed electrons from a metal surface. Electrons from a heated filament were accelerated by a voltage and allowed to strike the surface of nickel metal.

The electron beam was focused on a nickel target that could be rotated to observe the dispersed electrons’ angular dependency. Their electron detector (known as a Faraday box) was positioned on an arc and could be rotated to observe electrons from various angles. They were taken aback when they discovered that the intensity of the dispersed electron beam had a peak at some angles. The Bragg law could be used to calculate the lattice spacing in the nickel crystal based on this peak, which showed wave behaviour for the electrons.

With rising accelerating voltage, the experimental data above, replicated above Davisson’s article, reveals recurrent maxima of scattered electron intensity. This information was gathered at a certain dispersion angle. The relationship is calculated using the Bragg law, the deBroglie wavelength expression, and the kinetic energy of the accelerated electrons.

1electron wavelength=n2d sinθBragg law=phdeBroglie relationship=2mEh=2meVh

Acceleration through Voltage V

An accelerating voltage of 54 volts produced a distinct peak at a scattering angle of 50° in the historical data. The Bragg law’s angle theta for that scattering angle is 65°, and the computed lattice spacing for that angle is 0.092 nm. The wavelength as a function of voltage relationship is empirically determined for that lattice spacing and scattering angle.

1nm=n2d sinθ=0.815V

Electric Gun

An electron gun is a Tungsten filament that emits electrons through thermionic emission, or when heated to a specific temperature.

Electrostatic Particle Accelerator

The electrons are accelerated at a known potential using two oppositely charged plates (positive and negative plate).

Collimator

The accelerator is housed in a cylinder with a limited route for electrons running parallel to its axis. Its purpose is to prepare an electron beam that is narrow and straight (collimated) for acceleration.

Target

A Nickel crystal is the target. The electron beam is fired normally on the Nickel crystal.The crystal is positioned in such a way that it can be spun around a central axis.

Detector

The dispersed electrons from the Ni crystal are captured using a detector. As indicated in the diagram above, the detector can be moved in a semicircular arc.

Conclusion

The Davisson—Germer experiment (1927) was the first time wavelengths of electrons were measured. C. J. Davisson of the Bell Research Laboratories shared the Nobel Prize in Physics for 1937 with George P. Thomson of the University of Aberdeen in Scotland, who discovered experimental evidence of electron diffraction independently. Wave-particle duality, according to the Copenhagen Interpretation of Quantum Mechanics, causes particles to display wave-like properties such as spatial extension and interference.

Lester H. Germer (1896–1971) and Clinton J. Davisson (1881–1958) studied the reflection of electron beams on the surface of nickel crystals. When the beam hits the crystal, the electrons are scattered in all directions by the nickel atoms. The intensity of the scattered electrons was measured in relation to the incident electron beam by their detector. The dispersed electrons in their normal polycrystalline samples were distributed in a highly smooth angular distribution. One of their samples was accidently recrystallized in a laboratory mishap in early 1925, resulting in a practically monocrystalline structure. As a result, strong peaks appeared in the angular distribution at particular angles. Other monocrystalline materials, as Davisson and Germer soon discovered, exhibited similar aberrant patterns, which differed depending on the chemical composition, angle of incidence, and orientation of the sample. When Davisson visited a meeting of the British Association for the Advancement of Science in Oxford in late 1926, they finally realized what was going on. During the occasion, Born discussed de Broglie’s matter-waves and Schrodinger’s wave mechanics.The quantum mechanical predictions for electron wavelength as a function of momentum p: = h/p were perfectly validated by their subsequent measurements. However, unlike G.P Thomson’s, their initial tests were carried out in the context of practical materials research on vacuum tube filaments, rather than under any specific theoretical guidance.