Structural and electronic properties of rare earth silicides on silicon(001): Nanowires and three-dimensional islands

Deposition of rare earth (RE) metals on the silicon(001) surface at elevated temperature results in the formation of RE silicide islands coexisting with a reconstructed substrate surface. This thesis presents the growth behavior of holmium, samarium, and dysprosium on Si(001) and the electronic properties of the resulting surface structures.; The growth of Ho and Sm on Si(001) at 600°C was studied using scanning tunneling microscopy (STM) and low energy electron diffraction.; Ho grows in a Stranski-Krastanov mode with highly elongated nanowires (NWs) and a 2 x 4 reconstructed substrate at low metal coverage. As the coverage increases, three-dimensional (3D) compact silicide islands coexist with the NWs. A 2 x 7 two-dimensional (2D) phase appears in the medium coverage range, and it always coexists with the 2 x 4 phase. Scanning tunneling spectroscopy (STS) data show that HoSi2 NWs are more metallic than the 3D silicide islands or the reconstructed substrate.; Sm/Si(001) induces two different surface reconstructions: a lower coverage 2 x 3 phase and higher coverage 3 x 2/c(6 x 2) phases. In the high coverage regime, large 3D silicide islands are observed instead of elongated NWs.; The topographical evolution of 3D Dy silicide structures and the 2D reconstructed surface in the temperature range of 600∼750°C was investigated by STM and low energy electron microscopy (LEEM). The initial surfaces were covered in the 2 x 7 superstructure plus NWs of uniform width defined by the 2 x 7 unit cell. Post-growth annealing at 700°C increases the number of 3D islands and the average island size.{09}At the same time, the number of NWs decreases and surface reconstruction is swept away. Therefore, 3D silicide islands are a stable phase whereas NWs are a metastable phase at 700°C.; Ex-situ transport properties of the grown RE silicide films were correlated with film morphology as observed by STM. A 1 nm thick film of interconnected DySi2 islands shows surface resistivity at 4.2 K similar to the reported bulk silicide value. A sample with sparse, disconnected islands shows higher surface resistivity than the 1 nm film but lower than that of the clean Si surface.