Davisson–Germer Experiment

One-Sentence Significance

The Davisson–Germer experiment observed electron diffraction from a nickel crystal, confirming the de Broglie relation for matter waves.

What Was Measured

Electrons were scattered from a crystalline nickel target. The scattered intensity showed angular maxima characteristic of wave diffraction from a periodic structure.

The relevant matter-wave relation is

$$\lambda = \frac{h}{p}.$$

Crystal diffraction angles are compared with Bragg-like conditions such as

$$2d\sin\theta = n\lambda.$$

What It Showed

Electrons, which had been treated as particles carrying charge and mass, also exhibit wave-like diffraction with the wavelength predicted by de Broglie. This was strong evidence that wave mechanics applies to matter, not only to light.

What It Did Not Show By Itself

The experiment did not say electrons are ordinary classical waves spread through space. Detectors still record localized events. It showed that electron propagation amplitudes have wave character and can interfere according to wavelength and phase.

It also did not derive the Schrödinger equation by itself. It supported the matter-wave hypothesis that the Schrödinger theory then organized.

Modern Interpretation

Electron states have momentum-space and position-space representations connected by Fourier transform. A crystalline lattice provides many coherently spaced scattering centers, so the outgoing amplitude has diffraction maxima tied to the electron wavelength.

Modern electron diffraction and electron microscopy build directly on this wave nature of matter.

Canonical Links

• Full Historical Page
• Electron Diffraction
• Momentum-Space Representation
• Wave Packets
• Fourier Transform
• Double-Slit Experiment
• Probability Amplitudes

Common Myths

• Electron diffraction means electrons are classical water waves.
• Matter waves only apply in special crystals. Crystals make the wave nature easy to observe.
• The de Broglie wavelength is optional. It is central to the quantum relation between momentum and phase.
• Localized detection rules out wave behavior. Quantum mechanics combines localized detection with interference amplitudes.

Quick Check

What happens to the de Broglie wavelength when electron momentum increases?

Solution

Since $\lambda=h/p$, increasing momentum decreases the wavelength. Higher-momentum electrons therefore diffract through smaller angles for the same lattice spacing.

References

• C. Davisson and L. H. Germer, “Diffraction of Electrons by a Crystal of Nickel,” Physical Review 30, 705-740, 1927.
• G. P. Thomson, “Experiments on the Diffraction of Cathode Rays,” Proceedings of the Royal Society A 117, 600-609, 1928.
• L. de Broglie, “Recherches sur la theorie des quanta,” PhD thesis, University of Paris, 1924.