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| Identifier | 000326881 | ||||||
| Title | Μελέτη πλεγμάτων άμορφου και νανοδυναμικού άνθρακα με τη μέθοδο της ισχυράς δέσμευσης | ||||||
| Alternative Title | Tight-binding molecular dynamics studies of amorphous and nanostructured carbon networks | ||||||
| Author | Μαθιουδάκης, Χρήστος | ||||||
| Thesis advisor |
Κοπιδάκης, Γεώργιος
Κελίρης, Παντελής |
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| Abstract |
As an introduction to the subject, we first present the elemental properties of carbon, its electronic structure and hybridizations, and the various forms that can be attained by carbon either in the solid state or in nanostructured configurations. Next, we present the theory of the tight-binding method and the two specific models used in this work. We also present the methodology for the computer generation of our networks, as well as the tools used for their analysis. Initially, we study the microstructure of amorphous carbon. We extract the structural parameters of our networks and calculate the distribution functions of bond lengths and bond angles, and perform a statistical analysis of rings. We find that the basic characteristics of the microstructure are in excellent agreement with results from first-principle calculations. After establishing the reliability of our methodology, we study the structural and elastic properties of our amorphous carbon networks. The main finding about the material density is that it has a linear dependence on the sp3 tetrahedral fraction, in good agreement with experimental work and other theoretical calculations. Also, we extract for the first time accurate relations between the bulk modulus and the mean coordination (or equivalently the density) and the mean bond length in the amorphous network. These relations, in a power-law form, are in excellent agreement with mean-field theories for the elastic properties. We continue by investigating the electronic and optical properties of amorphous carbon. Our major contribution here is the development of a methodology to calculate the optical constants from the tight-binding wavefunctions. Initially, we calculate the electronic density of states and the dielectric function, and we then extract the optical gaps and the Urbach energy, associating them with the degree of disorder in our networks. We compare to the literature where it is feasible. Finally, the dissertation is concluded by applying the above well-tested methods to the case of nanostructured carbon. |
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| Language | English | ||||||
| Issue date | 2008-05-07 | ||||||
| Collection | School/Department--School of Sciences and Engineering--Department of Materials Science and Technology--Doctoral theses | ||||||
| Type of Work--Doctoral theses | |||||||
| Permanent Link |
https://elocus.lib.uoc.gr//dlib/9/7/5/metadata-dlib-2aee7668ff6a6269ad182df2d3d63c79_1237538994.tkl
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| Views | 355 | ||||||
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