Formation, properties and photoemission study of ternary silicides

We have carried out an experimental study of the formation, structural and electronic properties of thin film and bulk ternary silicides. Ternary and binary silicides films were grown by rf sputtering and annealed using rapid thermal processing in high vacuum (P $\sim$ 10$\sp{-7}$ Torr.). The bilayers Ti/Ni and Ni/Ti on Si(100) lead to the formation of the ternary phase Ti$\sb4$Ni$\sb4$Si$\sb7$. Thin films of Nb on Si(100) lead to the formation of NbSi$\sb2$ at 720$\sp\circ$C. The variation of the sheet resistance vs. temperature is correlated to grain growth. The lowest resistivity measured (38 $\mu\Omega$-cm) is among the lowest reported for NbSi$\sb2$. Bilayers Ni/Nb and Nb/Ni on Si(100) and Ni/NbSi$\sb{\rm 2}$/Si(100) lead to phase separation. V phase Nb$\sb4$Ni$\sb4$Si$\sb{\rm 7}$ is grown from the sequence Nb/Ni/Si/SiO$\sb2$/Si(100). SiO$\sb2$ is used as a buffer to limit the consumption of Si. The crystalline parameters, atomic positions, unit cell, and temperature factors of V phase Ti$\sb{\rm 4}$Ni$\sb4$Si$\sb7$ have been precisely determined using neutron powder diffraction accompanied by Rietveld analysis. From the arrangement of the atoms in the unit cell and their inter-bond distances, we have found that Si atoms are nearest neighbors to Ti and Ni. We found that Ti-Si and Ni-Si hybridization is much stronger than that of Ti-Ni. Synchrotron radiation-based photoemission was used to study the electronic structure of ternary transition metal silicides: Ti$\sb4$Ni$\sb4$Si$\sb7$, Ti$\sb4$Co$\sb4$Si$\sb7$, TiFeSi$\sb2$ and Nb$\sb4$Ni$\sb4$Si$\sb7$ prepared by arc-melting. In all cases, the near-noble metal contribution to the DOS dominates the valence band. The main non-bonding 3d features move toward the Fermi level as Ni is replaced by Co and Fe. The DOS near E$\sb{\rm f}$ of the ternary compounds is greater than those of Ni, Co or Fe mono- and disilicides. The relative weakness of the Ni 3p-3d satellite in the ternary compounds is consistent with the conclusion that there are fewer unoccupied Ni 3d states near E$\sb{\rm f}$. The Si 2p core level becomes more symmetric and moves to a lower binding energy when Ni is substituted by Co and by Fe, suggesting that Ti$\sb4$Ni$\sb4$Si$\sb7$ is more metallic than the other ternary transition metal silicides