Towards a Mn–Co surface alloy: Scanning Tunneling Microscopy (STM) study of Co adsorption on Si(100) and its interaction with Mn wires

Abstract

The interaction of Co with the Si(100)-2×1 surface is studied with Scanning Tunneling Microscopy (STM), followed by investigation of Co deposition on Si(100)-2×1 decorated with Mn wires, and the co-deposition of Mn and Co. The Co deposition (0.03 to 0.1 ML) leads to the formation of a significant number of defects, and the concentration of A and B-type defects increases independently of Co-coverage from 2 to 4% before Co-deposition by an average of 8.4%. This is attributed to an equilibrium reaction between defect creation, through interaction of Co with the surface and associated ejection of Si-atoms, and annihilation of defects with Si-surface atoms. Co occupies preferentially (70%) the asymmetric subsurface sites with the remainder sitting in symmetric subsurface sites. The Co-induced formation of defects is also observed in the presence of Mn wires, and during the co-deposition of both elements. Deposition of Co on the Si-surface decorated with Mn wires leads to the introduction of numerous kinks and therefore, overall shorter Mn wires; the underlying mechanism remains an open question. A comparison of the density of Co atoms in a capture zone containing all atoms adjacent to a wire and on the free surface in between Mn wires, illustrates the preference for Co atoms to decorate Mn wires. This can be interpreted as the early stages of alloying. The co-deposition of Mn and Co leads to a very similar picture: short Mn wires coexist with a defect-rich Si surface, and a Co-atom distribution similar to the sequential deposition is observed albeit with a stronger tendency to form small clusters. The strong driving force for the Mn wire formation is therefore the critical parameter in controlling the overall Mn and Co atom distribution on the surface. These experiments will enable us in the future to develop an in-depth understanding of the magnetic exchange interaction in composite layers.