| Abstract |
The scope of the present dissertation is to simulate Carbon nanocomposites and nanostructures, and explore their characteristics. In order to reach this goal, Monte Carlo simulations within the empirical potential approach, and Tight-Binding Molecular Dynamics utilizing two different Hamiltonians were used. A few details concerning these methods and the modeled atomic interactions are included in the first chapter. It is followed by the main trends governing the two components of the simulated structures, i.e. single phase amorphous Carbon and crystalline Carbon. The former is the host matrix that includes the latter. Their structure and properties are crucial for the behavior of the whole composite. The energetics and stability of carbon nanocrystals of various forms and sizes embedded in an a-C matrix are firstly investigated. Diamond crystallites and schwarzites (negatively curved sp2 configurations) are found stable in high and low density a-C matrices, respectively. Other structures are metastable. The interaction of the host matrix with the core crystallites and their stress states is also analyzed. The stability of diamond nanocomposites allows the further exploration of their mechanical properties. The bulk moduli for dense structures are considerable higher than in the case of a C. The diamond/a-C composites have also high strength, which makes them suitable for many mechanical applications. Under the effect of tensile or shear load they break in a similar manner to a-C. Hence, the embedding of nanodiamonds enhances the elastic properties, but not the ideal fracture of the whole structure. Results on Carbon nanocomposites with nanotube inclusions are also presented. A very interesting feature iw the formation of a curved graphitic wall surrounding the nanotube. The most stable structures have intermediate densities, high anisotropies and increased elastic moduli compared to a C. The properties are highly affected by the tube diameter, rather than its chirality. Finally, the pressure effects on free-standing Carbon nanostructures and their structural deformations are analyzed. Some additional issues on the shape of diamond nanocrystals embedded in a-C, and the electronic density of states of these structures are covered in the last two sections.
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Theoretical investigation of the stability and mechanical properties of nanostructured amorphous carbon
