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| Author(s): |
Tiago Botari
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Instituto de Física Gleb Wataghin |
| Defense date: | 2016-02-29 |
| Examining board members: |
Douglas Soares Galvão;
Luiz Eduardo Moreira Carvalho de Oliveira;
Antonio Riul Júnior;
Ado Jorio de Vasconcelos;
José Arruda de Oliveira Freire
|
| Advisor: | Douglas Soares Galvão |
| Abstract | |
We present here three works on distinct two-dimensional materials. Our investigations were carried out using the following computational simulation methods: Density Functional Theory (DFT), Density Functional Tight-Binding and classical reactive molecular simulations. We divided the thesis to three parts: I. Mechanical Properties and Dynamical Fracture of Silicene; II. Investigation of Graphene Healing Mechanisms, and; III. Thermodynamical Stability of Carbon Nitride Materials. In part I, mechanical properties and dynamical fracture of silicene membranes were investigated via computational simulations. The studied models consist of armchair/zigzag suspended silicene membranes. The larger structures were chosen to have around 1000 atoms. Initially, we investigated the minimum energy structure using DFT, DFTB and ReaxFF. We found a good agreement of minimum energy structures comparing the three methods and other results reported in the literature. Afterwards, we investigated the stretching process using molecular dynamic simulations with DFTB and ReaxFF methods. Then, using the data from these molecular dynamics simulations, we calculated the Young's modulus, Poisson's ratio and critical strain values among others. We obtained that the Young's modulus of silicene is 10 times smaller than the one for graphene under similar conditions. Also, by analysing the fracturing process, we observed some boundary reconstructions for the armchair membranes. We also addressed the stress distributions, unbuckling mechanisms, and the fracture dependence on the temperature. We also analysed the differences due to distinct edge morphologies, namely zigzag and armchair. In part II, classical reactive molecular dynamic simulations were carried out to investigate the graphene healing mechanism. Using a computational model, we simulated the conditions of recent experiments of reconstruction of defective graphene, including the dependence of temperature and heating effects due to electron beam interactions with the system. Our results show that it is necessary a source of carbon atoms to trigger the graphene healing mechanism. Besides that, these atoms must have sufficient energy to overcome the energy barrier of the defect boundaries. We obtained perfect reconstruction of a defect under two conditions: high temperature through the whole system or with the aid of a local heating source at room temperature, for certain energy rates. In part III, different carbon nitride structures were investigated, such as oligomers, molecular crystals, polymeric crystalline phases and graphene-like phases. We carried out calculations using density functional theory (DFT), as well as methods beyond DFT. We optimized all structures, and investigated their thermodynamic stability and electronic properties. Our results showed that the polymeric melon phase should be obtained in the common synthesis process reported in the literature. Many of these experimental reports incorrectly identified the synthesized material as g-heptazine. We also investigated the electronic properties for the melon structure and g-heptazine (AU) | |
| FAPESP's process: | 12/12448-3 - Tribological properties of graphene, boron nitride and silicene: an investigation by reactive molecular dynamics |
| Grantee: | Tiago Botari |
| Support Opportunities: | Scholarships in Brazil - Doctorate |