| Iron silicide nanowires (NWs) were grown and studied in this work. We have found that self-assembled epitaxial iron silicide NWs grown on Si(110) can be converted from a cubic s-phase to an orthorhombic beta-phase FeSi 2 by annealing at 800°C for 1 hour. The transformation temperature of 800°C is considerably higher than that observed in thin films (200-500°C), due to the small thickness and large interface area of the NWs, which stabilize the s-phase. These two phases are metallic vs semi conducting, respectively, in thin films. The NWs have average dimensions of 5nm high x 10nm wide x mum long, as measured with ex situ atomic force microscopy. High resolution electron microscopy identifies the crystal structure as cubic s-FeSi2 with orientation FeSi2 ( 111) // Si(111), FeSi2 <110> // S1<110>.;The s-phase shows magnetic response of 0.3 Bohr magneton per iron atom at 2K, which are thought due to surface effects and/or stoichiometry, since bulk s-phase is not ferromagnetic. This magnetic response in epitaxial FeSi 2 NWs opens up the possibility for high-density data storage and logic applications.;We developed a new sample structure, nanodots on NWs, for NWs resistance measurement to avoid NW surface oxidation when removed from ultrahigh vacuum (UHV) chamber. A simple method using cleaved thin silicon strip as shade to make macro electric pad is practical and works for our resistance measurement scheme by conductive atomic force microscope (c-AFM). W-tip is the right choice for this work, and offered useful data. From length-dependent two-probe resistance measurement, iron silicide NWs resistivity, rho, was estimated to be 150 mu O·cm This higher resistivity than that of bulk iron silicide (60-80 mu O·cm) is believed due to contact resistance, Rc, and/or interface scattering along NW edge. Measurement using ex situ electron-beam lithography pattern shows even higher resistivity (∼500 mu O·cm) due to large contact resistance. |
