Self-assembled lead atomic nanowires on pre-structured Sm/Si(1 1 1) interfaces

The (3 × 2) and (7 × 1) chain structures induced by the adsorption of Sm atoms on Si(1 1 1) substrate are used as template to create self-assembled nanowires. Their structure models are based on an appropriate combination of honeycomb chain channel (HCC) and Seiwatz Si chains. In our study, Pb atoms are evaporated on these pre-structured surfaces. Our STM observations reveal the presence of well-aligned Pb nanowires running along the [ 1 1 ¯ 0 ] direction on the (7 × 1)-Sm/Si(1 1 1) structure whereas they are not formed on the (3 × 2)-Sm/Si(1 1 1) phase whatever the growth conditions. A thorough examination of the high resolution STM images reveals that the Pb preferentially grows onto the Seiwatz chains along the Sm rows, suggesting that the Seiwatz chains are the most reactive sites on the (7 × 1)-Sm/Si(1 1 1) surface. The difference of Pb reactivity on these surfaces illustrates the influence of bond energy and strain on the surface induced by the both HCC and Seiwatz Si chains in the growth of nanowires. The influence of thermal conditions on the Pb nanowires formation is also discussed.