Iron disilicide growth on Si(111): a scanning tunneling microscopy investigation

The growth of Fe on Si(111)(7 x 7) has been studied by scanning tunneling microscopy as a function of the deposited thickness using both solid phase epitaxy and reactive deposition epitaxy. At submonolayer deposition of Fe and subsequent annealing at 600-degrees-C, flat islands of silicide with hexagonal symmetry become visible above the Si(7 x 7) reconstructed surface which supplies a bond length reference scale for the alloy. The islands tend to grow at the expense of the silicon substrate, creating a large number of surface steps. Atomically resolved images of the islands show that in all cases a cubic (2 x 2) phase is formed. The interplanar (111) distance is compatible more with the FeSi (CsCl structure) than with the FeSi2 (CaF2) epitaxy. The orthorhombic beta phase does not form under the present growth conditions.