Anisotropic Strain-Mediated Growth of Monatomic Co Chains on Unreconstructed Regions of the Au(111) Surface

Single-metal-atom chains, the ultimate one-dimensional (1D) structure, have intriguing physical and chemical properties. However, their controllable and massive production remains challenging as it requires the positioning of individual atoms with atomic precision. Here, by using a two-step molecular beam epitaxy method, we successfully fabricate single-cobalt-atom chains on a metal surface, where organic molecules are first sublimated onto heated Au(111), followed by deposition of Co atoms. Adsorption of 8OH-TPB (octahydroxyl tetraphenylbenzene) on Au(111) induces surface reconstruction transition from a herringbone to a triangular pattern. Co deposition leads to the formation of 1D √3R30° chains with a cross section of only one atom propagating along the [11̅0] direction, which are separated from each other by a lateral spacing of 7-10 times the lattice constant of Au(111). The growth mechanism lies in the surface strain anisotropy induced by the strong Co-Au bonding, where the distance between the two Au atoms bridged via a Co adatom is significantly enlarged, while the Au-Au distance along the Co chain remains almost intact. The observed chain length distribution can be interpreted in terms of electronic scattering vectors at the Fermi surface of the Au(111) surface states.