In situ resistivity of endotaxial FeSi₂ nanowires on Si(110)

We present in situ ultra-high vacuum measurements of the resistivity ρ of self-assembled endotaxial FeSi₂ nanowires (NWs) on Si(110) using a variable-spacing two-point method with a moveable scanning tunneling microscope tip and fixed contact pad. The resistivity at room temperature was found to be nearly constant down to NW width W=4nm, but rose sharply to nearly double the bulk value at W=3nm. These data are not well-fit by a simple Fuch-Sondheimer model for boundary scattering, suggesting that other factors, possibly quantum effects, may be significant at the smallest dimensions. For a NW width of 4nm, partial oxidation increased ρ by approximately 50%, while cooling from 300K to 150K decreased ρ by approximately 10%. The relative insensitivity of ρ to NW size or oxidation or cooling is attributed to a high concentration of vacancies in the FeSi₂ structure, with a correspondingly short length for inelastic electron scattering, which obscures boundary scattering except in the smallest NWs. It is remarkable that the vacancy concentration persists in very small structures.