Strength of metals at the Fermi length scale

Using silver and gold, we have measured the size-dependence of the yield strength of atomic-sized samples as small as a single-atom bridge, with pico-level resolution in the applied force and displacement. The strength approaches theoretical values as the diameter of the sample becomes comparable to the Fermi wavelength of electrons (∼0.5 nm); in the limit of a single-atom bridge, the strength is over four orders of magnitude higher than in bulk single crystals. Results provide direct evidence for Pauling's prediction of bond stiffening with reduced atomic coordination. Beginning with a single-atom bridge, strength evolves in a staircase manner in Ag, instead of the intuitively assumed continuous approach to a saturating bulk value.