| Low-dimensional nanostructures have been attracting considerable interest for many years due to their unusual physical properties. Recently it is found that the rare earth(RE) metal silicide nanostructures, such as Er, Dy, Gd, Sc etc., could self-assemble on the Si(001) substrate by depositing low coverage RE metal and then post-annealing at elevated temperature. Because the RE metal silicides are of high conductivity and low Schottky barrier on n type silicon substrate, these RE metal silicide nanostructres have great potential applications in future electronic and optoelectronic devices technology.In such a background, this thesis is mainly focused on the growth morphology and internal structures of erbium silicide nanostructures self-assembled on the Si(001) substrate. The major works and innovation are listed below:1. Ultra-high vacuum scanning tunneling microscopy(UHV-STM) is employed to investigate in-situ the morphology of erbium silicide nanostructures, and by means of adjusting the growth conditions such as coverage, annealing temperature and annealing time, it is realized to control the morphology of the silicide nanostructures. Furthermore, the internal crystalline structures of these nanostructures are studied using high resolution transmission electron microscopy(HRTEM). The results show that the erbium silicide nanowires formed at the lower annealing temperature are of hexagonal structure, while the nanoislands formed at the higher temperature are of tetragonal structure. The measured lattice parameter indicates the lattice mismatch between Er silicide nanowires and silicon substrate is 4.7%-5.0%, less than that of the theoretical value (6.5%), which implies much larger strain along the ErSi2[0001] direction. Meanwhile, the measured lattice mismatch between Er silicide nanoislands and substrate is 2.4%, also less than the theoretical value,3.5%, which also indicates the strain in the nanoislands with tetragonal structure. Additionally, the tetragonal and hexagonal structures are found coexisting in the nanoislands, and they exactly match in the atomic configuration.2. The morphology evolution and the internal structure transformation are studied using STM and TEM. In STM measurements, the morphology evolution of nanwires to nanoislands are observed during the annealing process with the duration time increased from 10 to 180 minutes. The TEM results indicate there is a structural transition from A1B2-type to ThSi2-type crystalline structure. In particular, the experimental results prove that the hexagonal A1B2-type structure in Er silicide nanowires is a metastable phase grown on the Si(001) substrate. And it is found that Er silicide nanwires usually immerse into silicon substrate during their growth on the surface. The kinetic factors such as immersion and coalescence are attributed to the structural transition from hexagonal to tetragonal structure, which lead to the nanowries evolving into the nanoislands.3. A novel growth method comprising several cycles of deposition and annealing is developed to get high quality Er silicide nanostructures. For the nanoislands, the results indicate that three dimensions and the density of nanoislands continue to increase during the whole cycling growth. While for the nanowires, the second cycle of growth not only contributes to a higher density, but also keeps Er silicide in the nanowire-like shape rather than transforming into nanoislands. The experimental results show the nanowries and nanoislands formed in the first cycle of growth have the template effect during the later cycles of growth. Obviously, the new growth method is helpful to the development of new devices...
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