Nickela

Nickela raises her nickel-crystal shield, and a spray of electrons bounces off as a single bright beam at 50 degrees.

The Physics

At Bell Labs in 1927, Clinton Davisson and Lester Germer fired slow electrons at a single crystal of nickel and measured how many bounced off at each angle. At 54 eV they found a sharp peak at about 50°: a diffraction peak.

Treating the surface rows of atoms, spaced 0.215 nm apart, as a grating gives a wavelength of 0.165 nm. De Broglie's formula at 54 eV gives 0.167 nm. Electrons behave as waves.

d sin φ = λ and λ = h / √(2m_eE)

• d: spacing of surface atom rows (0.215 nm)
• φ: scattering angle of the peak (about 50°)
• λ: electron wavelength (m)
• h: Planck constant (J s)
• m_e: electron mass (kg)
• E: electron kinetic energy (54 eV)

Davisson & Germer, “Diffraction of electrons by a crystal of nickel”, Physical Review 30, 705 (1927).

Honest caveat: It was not the only proof: G. P. Thomson independently saw electron diffraction in 1927.

On the shirt

Front: Nickela, the pixel-art character, with “ELECTRONS DIFFRACT”. Back: the 54 eV peak at 50°, the grating and de Broglie wavelengths, and the 1927 Physical Review paper. Printed on a unisex tee.