1.21 Particle-Wave Duality:
Davisson–Germer Experiment
Both the electromagnetic radiation (photons) and particles exhibit a particlewave
duality and both may be characterized with wavelength λ and momentum
p related to one another through the following expression
λ = h
p
, (1.56)
where h is the Planck’s constant.
In relation to particles, (1.56) is referred to as the de Broglie relationship
and λ is referred to as the de Broglie wavelength of a particle in honour of
Louis de Broglie who in 1924 postulated the existence of matter waves.
The wave nature of the electron was confirmed experimentally by Clinton
J. Davisson and Lester H. Germer in 1927 who set out to measure the
energy of electrons scattered from a nickel target. The target was in the form
of a regular crystalline alloy that was formed through a special annealing
process. The beam of electrons was produced by thermionic emission from a
heated tungsten filament. The electrons were accelerated through a relatively
low variable potential difference V that enabled the selection of the incident
electron kinetic energy EK.
• Davisson and Germer discovered that for certain combinations of electron
kinetic energies EK and scattering angles φ the intensity of scattered
electrons exhibited maxima, similarly to the scattering of x rays from
a crystal with a crystalline plane separation d that follows the Bragg
relationship (see Fig. 1.5) with m an integer
2d sin φ = mλ . (1.57)
• Similarly to Moseley’s work with Kα characteristic x rays (see Sect. 2.5.2),
Davisson and Germer determined the wavelength λe of electrons from the
measured scattering angle φ at which the electron intensity exhibited a
maximum.
• The measured λe agreed well with wavelengths calculated from the