- Person
- Otto Stern
- Lived
- 1888–1969
- Field
- Experimental physics
- From
- German-American
The story
In 1924 Louis de Broglie proposed that every particle of matter also behaves like a wave, with a wavelength that depends on its momentum. In 1927 Clinton Davisson and Lester Germer confirmed this for electrons. But whether something as heavy and complex as a whole atom or molecule could really act as a wave was still an open question.
Otto Stern had listed a test of de Broglie's idea among the goals of an ambitious research programme he set out in 1926 for his molecular-beam laboratory at the University of Hamburg. A first attempt with Friedrich Knauer, scattering helium and hydrogen beams from ordinary surfaces, gave only a hint of a diffraction peak. In the spring of 1929 Stern, working alone on the modified apparatus, observed diffraction of helium and hydrogen from a freshly split crystal of rock salt. With his long-time collaborator Immanuel Estermann he then used more perfect lithium fluoride crystals and obtained sharper peaks.
The decisive step came in 1931. Estermann, Otto Robert Frisch and Stern first sorted the atoms by speed, using either a crystal as a filter or a pair of rotating slotted discs, before scattering them from a second crystal. The diffraction peaks were now sharp enough to test de Broglie's formula precisely. At first the result was 3 per cent off. Only when the apparatus was taken apart did the team discover that the discs had 408 slots rather than the 400 the manufacturer had stated, and the corrected agreement was within 1 per cent. They were the first to show that de Broglie's relationship holds for atoms and molecules.
Stern considered these experiments his most important contribution to quantum mechanics and said he liked them best of all. The 2011 review of his career in Annalen der Physik counts the diffraction of matter waves by crystals, dated 1931, among his four key results.
The work also opened new paths. Unexpected dips in the diffraction patterns, which Frisch and Stern suspected were caused by atoms briefly sticking to the surface, were later explained by John Lennard-Jones and A. F. Devonshire. The effect, now called selective adsorption, is widely used to measure the forces between atoms and surfaces, and Stern's surface scattering experiments grew into a major area of surface science.
Why it matters
Atom diffraction laid early groundwork for atom optics and atom interferometry, fields that today power ultra-precise sensors and measurements.
About Otto Stern
Physicist whose molecular-beam method proved space quantisation in the Stern–Gerlach experiment and measured the proton’s magnetic moment; Nobel Prize in Physics 1943.
More about Otto Stern
- Otto Stern proved atoms obey quantum rules in 1922In February 1922 the Stern–Gerlach experiment split a beam of silver atoms cleanly in two, the first direct proof that quantum rules govern how atoms behave in a magnetic field.
- Otto Stern's lab trained Rabi, opening a path to MRIIsidor Rabi learned the molecular-beam technique in Otto Stern's Hamburg lab, and built on it the magnetic resonance method behind NMR, MRI and atomic clocks.
- Otto Stern made molecular beams a precision toolIn 1920 Otto Stern measured the speed of silver atoms in a vacuum, turning molecular beams, first used by Louis Dunoyer in 1911, into a precise tool for studying single atoms.
- Otto Stern found the proton is not a simple particleIn 1933 Otto Stern, Otto Frisch and Immanuel Estermann measured the proton's magnetism and found it unexpectedly large, the first sign that the proton has inner structure.
Sources
- Otto Stern (1888–1969): The founding father of experimental atomic physics Annalen der Physik / arXiv
- Otto Stern Wikipedia
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