Epitaxial Growth And XPS Analysis Of Iron And Manganese Silicides On Silicon Surface

Iron and manganese silicides, with novel physical properties, are promisingcandidates in the research for optoelectronic devices, fiber optic interconnection,infrared detectors and thermoelectric materials. In this paper, iron and manganesesilicides are formed on Si(111) and Si(110) surfaces with molecular beam epitaxymethod. A systematic study of the growth mechanism and electron structure of theiron and manganese silicides on silicon surface by a delicate control of growthparameters is a significant step toward their practical applications. The main resultscan be summarized as follows:(1) Several iron silicides can coexist on Si(111) surface between600℃and800℃. The density of stable nuclei nxdecreases with the rise of temperature or thedrop of deposition rate. The nucleation process of iron silicides meet with thetraditional nucleation theory. The polygonal plate-shaped p(2×2) phase transforms toc(8×4) phase at~700℃. In the optimized condition, by depositing~1.7ML Fe onSi(111) surface at a deposition rate of0.0067ML min-1at~775℃, the area of c(8×4)phase can reach1μm2. The I-V curves indicate that the c(8×4) phase and equilateraltriangle-shaped islands are semiconducting, the band gaps are~0.8eV and~0.9eV,respectively. Different from the c(8×4) phase and equilateral triangle-shaped islands,the rod like islands are metallic.(2) The XPS study indicates that~47%of the iron silicides were oxidized afterexposure to the atmosphere for about10min. The two peaks at the binding energy of706.9eV and719.7eV correspond to Fe2p3/2and2p1/2peaks of iron silicides,respectively. Compared to the Fe2p doublet for elemental Fe, the Fe2p doublet forsilicide phase is shifted to higher binding energies side by~0.2eV. On the contrary, the Si2p3/2peak (98.9eV) is shifted to lower binding energies side by~0.3eVcompared to the bulk Si-sp3state (99.2eV). The shift of the Si2p3/2peakdemonstrates that the chemical state of Si is changed with the formation of ironsilicide.(3) The STM research demonstrates that MnSi film is~0.9nm high with asurface of33reconstruction, and that the MnSi1.7nanowires are about~3nmhigh,16~18nm wide and500~1500nm long. XPS analysis of Mn2p core levelsindicate that the spectra of manganese silicides are clearly different from that of themanganese clusters. The Mn2p level of MnSi film and MnSi1.7nanowires exhibit anegative chemical shift of~0.5eV from elemental Mn due to the contribution ofMadelung potential. The MnSi film and MnSi1.7nanowires were oxidized after anatmospheric exposure of about10min. By means of curve fitting, we obtain that theoxidized proportion of MnSi film and MnSi1.7nanowires are~53%and64.9%,respectively. However, the oxidation reisitance of the manganese silicides is muchbetter than that of the Mn clusters, which is probably due to the protection effect ofthe SiO2layer formed on the manganese silicides and the smaller surface to volumeratio of the manganese silicides comparing with the clusters.