Self-organization of atom wires on vicinal surfaces*

Self-organization is possibly the best way to produce nanostructures in large quantities. This also holds for the ultimate 1D system, atom wires; they can be self-assembled in large arrays on vicinal Si surfaces. Such atom wire systems often show intriguing electronic properties such as competing charge density waves and spin-orbit split one-dimensional bands. However, because of their low dimensionality, these wires also frequently show profound thermodynamic fluctuations that limit their \textit{structural} uniformity and have a large influence on their electronic properties. Therefore, in this talk I will focus on structural fluctuations in Ga atom wires self-organized on the Si(112) surface. In these atom wires, strain-relieving adatom vacancies self-organize into meandering vacancy lines (VLs) similar to the well-known nx2 superstructures for Ge on Si(100). The average spacing between these line defects can be experimentally controlled continuously by adjusting the chemical potential $\mu $ of the Ga adatoms. Significant VL correlations are discovered in STM experiments that cannot be captured within a mean field analysis. These structural flucuations are well described by a new lattice model that combines Density Functional Theory (DFT) calculations for perfectly ordered structures with the fluctuating disorder seen in experiment, and the experimental control parameter $\mu $. This hybrid approach of lattice modeling and DFT can be applied to other examples of line defects in hetero-epitaxy, especially in cases where correlation effects are significant and a mean field approach is not valid.