Formation of manganese nanostructures on the Si(100)-(2 x 1) surface

The formation of Mn-nano structures on the Si(100)-(2 x 1) surface has been studied with scanning tunneling microscopy as a function of Mn-coverage. The room temperature deposition leads to the preferential formation of monoatomic Mn-wires at coverages below 0.3 ML. Isolated adatoms and ultrasmall clusters begin to appear at higher coverage and compete with the wire growth. The Mn-wires are always oriented perpendicular to the Si-dimer rows and consequently switch orientation at each step edge. The mean length of the Mn-wires increases with coverage, albeit the maximum wire length appears to be limited to about 20 times the Si-dimer line distance. The local Si-reconstruction adopts a p(2 x 2) structure in the vicinity of the Mri-wires, and remains in the (2 x 1) phase around the clusters. The STM images indicate that the Mn atoms within the wires are positioned in between the Si-dimers, while isolated Mn atoms prefer to bond on top of a Si-dimer. Several possible interpretations of the experimental data with respect to the Mn-wire and adatom bonding position are discussed. The co-existence of wire and clusters is tentatively assigned to a competition between different adatom bonding sites, and the wire growth itself is promoted by an anisotropic attachment favouring bonding to the wire ends. This study illustrates that Mn-nanostructures form on a Si(100) surface and strongly indicates the feasibility to grow single-layer Mn structures and delta-doped Mn-layers embedded in a Si matrix. (C) 2007 Elsevier B.V. All rights reserved.