1937 Nobel Prize in Physics
Reason for Award
for their experimental discovery of the diffraction of electrons by crystals
Laureates
United States of America
United Kingdom of Great Britain and Northern Ireland
Explanation
Electrons are tiny particles, yet they also behave like waves, just as light does. Mr. Davisson and Mr. Thomson shot electrons at a metal crystal to see if a wave pattern would appear. They observed that, like ripples bending around the posts of a pier, the electrons spread out in certain directions. This spreading pattern is called “diffraction” and proved that electrons act as waves. Modern electron microscopes and semiconductor technology build on this very discovery.
Related Keywords
electron diffraction
The intensity pattern produced when an electron beam interferes and scatters from a crystal lattice. Like X-ray diffraction, peaks appear at Bragg angles. Because electrons have short wavelengths, the method offers high spatial resolution, measuring inter-atomic distances and lattice defects precisely. At low energies it probes surface atom layers, while at higher energies it reveals bulk structure. It is indispensable for semiconductor fabrication and materials characterization.
wave–particle duality
The quantum-mechanical principle that microscopic entities such as light or electrons exhibit both wave-like and particle-like behavior depending on the experiment. Young’s double-slit and electron diffraction are classic demonstrations. The same object forms interference fringes yet registers impact points as particles. De Broglie generalized the idea, linking wavelength and momentum via λ = h⁄p. It underpins modern nanotechnology and quantum information science.
de Broglie wavelength
The wavelength associated with a particle’s momentum p, given by λ = h⁄p. Faster particles have shorter wavelengths, allowing finer structural probes. The high resolution of electron microscopes relies on this short wavelength. Agreement of measured λ with theory in diffraction experiments verifies quantum mechanics. The parameter is vital in particle-accelerator design and neutron-scattering research.
Bragg's law
The phase-matching condition for diffraction from crystal planes, expressed as 2d sin θ = nλ, where d is lattice spacing, θ the incident/scattering angle, and n an integer. It predicts the angles at which peaks occur in X-ray or electron diffraction. The equation is used in inverse analysis to determine unknown crystal structures. Davisson and Thomson showed that electrons obey this same law.
crystal lattice
A three-dimensional periodic arrangement of atoms or ions. Lattice constants and symmetry determine a material’s physical properties. By analyzing diffraction peaks, one extracts d-spacings and lattice systems. Line widths or shifts reveal defects or residual stress. The concept is fundamental in semiconductor devices and alloy development.
Davisson–Germer experiment
A pioneering 1927 experiment on electron diffraction. Accelerated electrons were reflected from a nickel crystal, and intensity was measured with a goniometer to test the wavelength–momentum relation. An accidental vacuum-tank rupture followed by re-annealing produced a single crystal, crucial for success. The observed Bragg peaks decisively confirmed electron wave behavior. The work directly led to the Nobel Prize award.
Thomson electron diffraction
George P. Thomson’s diffraction method using electrons transmitted through thin-film crystals. Concentric rings on a fluorescent screen allow precise determination of plane spacings. It became a precursor to transmission electron microscopy (TEM). The technique employs high-energy electrons to minimize multiple scattering. It supplied independent evidence for wave–particle duality.
quantum mechanics
The theoretical framework describing the microscopic world. Schrödinger’s equation and matrix mechanics govern a particle’s probabilistic wave function. Electron diffraction provided experimental backing for its basic concepts. Quantum mechanics underlies technologies such as semiconductors, lasers, and MRI. Its probabilistic interpretation and uncertainty principle challenge everyday intuition.
electron microscope
An instrument that illuminates specimens with electron beams to produce highly magnified images. The short de Broglie wavelength yields nanometer-scale resolution beyond optical microscopes. Transmission (TEM) and scanning (SEM) modes are most common. Diffraction patterns or elemental analysis (EDS) can be recorded simultaneously for multi-modal information. The technology rests on the discoveries of Davisson and Thomson.
Brillouin zone
The polyhedral first frequency region in reciprocal space of a crystal. It is used in calculating electronic band structures and phonon dispersions. Diffraction conditions can be interpreted as scattering to reciprocal-lattice points, with zone folding occurring at Brillouin zone boundaries. Electron diffraction data can sometimes indirectly estimate energies at symmetry points. The concept bridges theory and experiment in solid-state physics.