STM Investigations Of Sr/Si Surface System

Sr/Si surfaces play important role in the growth of crystalline high-k oxide on silicon substrate, which acts as buffer layer, forbidden substrate silicon oxidation during high temperature annealing process. Using Scanning Tunneling Microscopy (STM) we investigate the geometric and electronic structures of Sr/Si reconstruction surfaces at different substrates.In Sr/Si(100)-2×'1'and Sr/Si(111)-3×2 surfaces:, quazi-1D atom line motions were observed in room temperature STM images. Both of the metal atom motions along the valley channel formed from substrate silicon dimers. A plausible Sr/Si(100)-2×3 surface model was proposed based on STM and theoretical results. TiSi2 nano-iland growth on Sr/Si(100)-2×'1'substrate behave exotic phenomenon at different bias condition.The whole thesis divided into six chapters.In the first chapter, we mainly explain the invention, work principle, the development and expanding of STM groups. Further we explain the important principle of scanning tunneling spectra (STS) and dI/dV mapping technique in measuring the surface electrical property. After summarize the former work, we explain the main purpose of our investigation of Sr/Si systems.In the second chapter, we explain the detailed experiment procedure to growth well ordered Sr/Si(100) surface system. And we notice that the surface reconstruction depend prominently on the annealing temperature of substrate. Using in-situ elevated–STM we investigate the evolve trace of the surface from oxidation to metal dominant, and three typical stage observed in the high-temperature STM images. Three typical surface reconstructions can be noticed in the room temperature STM images; among these three surfaces two reconstructions have bias dependent property.In the third chapter, after comparing the room temperature Sr/Si(100)-2×3 reconstruction surface STS and dI/dV mapping images, we proposed a plausible geometric structures based on theoretical results for the first time. We find that in the Sr/Si(100)-2×3 surface, substrate silicon have large arrangement , silicon dimer of Si(100)-2×1 substrate broken and forming new dimer, this well explain the contradict between XPS and formed theoretical results. To investigate the oxidation behavior of this Sr/Si(100)-2×3 surface, we exposed the clean surface to molecular oxygen, and we find that there have four typical reaction sites in the initial oxidation stage, among them one oxidation sites behave metallic property which was two-molecular oxidation product confirmed by theoretical results, and the other three configuration was single molecular oxidation products.In the fourth chapter, we investigate the electronic and dynamic property of Sr/Si(100)-2×1 surface. We find that the first layer atoms of this surface behave fluid-like property at room temperature STM images. That is we observe atom motion along the silicon dimer row direction. Furthermore, this motion was also observed at temperature of 80K, and confirm quazi-1D property of Sr/Si(100)-2×1 surface.In the fifth chapter, we investigate the Sr/Si(111)-3×2 surface growth on Si(111)-7×7 substrate. After analysis the electrical and geometric structure, we believe this surface reconstructed on the HCC model. Especially in this surface we observed quazi-1D atom motion at room temperature, and this quazi-1D phenomenon arouse from the room temperature activation of Sr atoms along the channel, which formed from reconstructed silicon atom lines.In the sixth chapter, we investigate the nano-island growth on the Sr/Si(100)-2×1 substrate. Metallic property was measures by STS for these islands. After analysis the typical dI/dV mapping of these islands, we find that different map appearing at different bias condition. After detailed analysis these mappings, we believe that these ilands were epitaxial C54-TiSi2 phase, and the different maps reflect the Ti and Si information separately.