• Appelfeller, Stephan

Abstract

Metallic nanowires grown by self-organisation on Si surfaces may be interesting for future applications in Si based nanotechnology, but they will also show unique physical phenomena, e.g. Peierls transitions or Tomonaga-Luttinger liquid behaviour, if they are characterised by a one-dimensional electronic structure. This thesis concentrates on the physical properties of Tb silicide nanowires, which are interesting for both future applications and study of one-dimensional physics. Terbium disilicides, which form after Tb deposition and annealing on Si substrates, are metals as bulk materials. Two different approaches are used to grow nanowires of these silicides. On one hand, presumably hexagonal TbSi2 nanowires form due to an anisotropic lattice mismatch on Si(001) substrates. On the other hand, extended hexagonal TbSi2 films form on planar Si(111) substrates and nanowire growth may be achieved by using substrates vicinal to Si(111), so-called Si(hhk) substrates, on which the film growth is disrupted by steps leading to structures confined in one direction. The nanowires on Si(001) are analysed using a multitude of different experimental methods, which was only possible due to intensive collaborations with the workgroup of Prof. Dr. Michael Lehmann (TU Berlin) and within the Forschergruppe 1700 funded by the Deutsche Forschungsgemeinschaft.Their growth is analysed in detail with scanning tunnelling microscopy and the parameter range, in which the nanowires predominantly form, is well defined by the Tb coverage and the annealing temperature. The nanowires may be overgrown by amorphous Si without structural change, but high-resolution transmission electron microscopy reveals structural changes for embedding in crystalline Si. Based on the cross-sectional data in combination with the surface science data, a new structural model is proposed for the nanowires. Not only the atomic, but also the electronic structure of the nanowires is analysed in detail. The nanowires are metallic, show a quasi-one-dimensional band structure and one-dimensional transport properties. On Si(hhk) substrates, nanowires only form for k > h. For the other offcut direction only elongated stripes with rough edges are observed after optimisation of the preparation parameters. Both stripes and nanowires are characterised by the two-dimensional electronic structure of the extended TbSi2, but with an anisotropic broadening presumably due to the confinement by their limited widths. An additional quasi-one-dimensional electronic structure is exclusively observed for preparations of samples showing the narrowest nanowires and possible corresponding surface structures, e.g. the nanowires or their edges, are discussed.

Topics

• Deposition
• impedance spectroscopy
• surface
• amorphous
• anisotropic
• transmission electron microscopy
• two-dimensional
• annealing
• one-dimensional
• band structure
• silicide
• Terbium