Growth of perfect and smooth Ag and Co monatomic wires on Pt vicinal surfaces: A kinetic Monte Carlo study

Growing perfect monatomic chains on surfaces is generally a hard task since it depends strongly on the experimental conditions and on the species used as templates or adsorbates. In the present study, the growth of Co and Ag monatomic wires on a Pt(9 9 7) vicinal surface is investigated over a large range of temperature. A semi-empirical potential is used to extract the main diffusion barriers responsible for the growth of Co and Ag wires on the Pt(9 9 7) vicinal surface. Kinetic Monte Carlo simulations are performed to investigate the wire formation at step-edges. We show that step decoration occurs at 150 K for Ag and at temperatures higher than 250 K for Co in agreement with growth experiments. If no interdiffusion is taken into account, Co and Ag behave similarly and perfect wires form between 150 and 500 K for Ag and between 300 and 500 K for Co. In the case of Co, an exchange mechanism leading to interlayer diffusion at step-edges is shown to strongly influence the temperature range for which the perfect wires are observed. An activation barrier of 0.65 eV for this mechanism is found to be adequate to reproduce the experimental features observed by Gambardella et al. [P. Gambardella, M. Blanc, L. Burgi, K. Kuhnke, K. Kern, Surf. Sci., 449 (2000) 93]. At higher temperatures, above 500 K, detachment from steps strongly hinders the wire formation at step feet. As a main conclusion, the exchange diffusion barrier can be extracted directly from the comparison between observation of step decoration and numerical simulations.