Bonding geometry of Mn-wires on the Si(100)(2 × 1) surface

The bonding geometry of monoatomic Mn-wires, which form on the reconstructed Si(100)(2 × 1) surface at room temperature, was investigated with scanning tunneling microscopy (STM). The Mn-wire structures are always perpendicular to the Si-dimer rows and the images exhibit a strong modulation of their apparent height as a function of bias voltage. The Mn-wire structures appear as depressions in the empty state images for bias voltages around 0.7 V, and as protrusions for all other bias voltages. It is suggested that the wire-images are defined by mixed Mn-Si states, either through a hybridization between the Mn d-states and the Si-p states, or backbonding from Mn-d electrons into the broken Si-dimer bond. The dominant bonding geometry shows that the Mn-wire maxima are positioned in between the Si-dimer rows, and a small percentage of about 20% is in registry with the Si-dimer rows, and might be described as defective wires. The experimental STM images cannot currently be described in a satisfactory manner with theoretical bonding models from the literature.