Theoretical Simulations And Calculations On Optoelectronic Properties And Applications Of Novel Carbon/silicon Based Nanomaterials

The carbon-based and silicon-based low-dimensional nanomaterials always exhibit superior optoelectronic properties, and are widely applied in modern high-tech field. Through forming composites by different materials, combination of Si and C atoms(alloying), as well as isomerization of the existing materials, the obtained novel carbon/silicon based nanomaterials show excellent physical and chemical properties that are superior to the existing ones, and show promising for application in optoelectronic and chemical fields.Using various approaches of theoretical computation, we perform theoretical simulations and calculations on the optoelectronic properties and potential applications of the recently fabricated or newly predicted low-dimensional carbon/silicon based nanomaterials. The study covers the zero-dimensional, one-dimensional and two-dimensional carbon/silicon based nanomaterials.In Chapter 1, the recent research status of low-dimensional carbon/silicon based nanomaterials is introduced. The existing low-dimensional carbon/silicon based nanomaterials are classified as carbon-based nanomaterials, silicon-based nanomaterials and carbon/silicon nanocomposites, and their species, physical properties and applications are summarized respectively, while the carbon/silicon based nanomaterials that are newly synthesized or predicted in recent years(such as core/shell nanostructure, siligraphene and nanographene) are highlighted.Chapter 2 summarizes the computational methods, theory and related softwares that are involved during the simulation and calculations on nanomaterials in this dissertation. The theoretical background and related computational softwares of density functional theory(DFT) and density-functional tight-binding(DFTB) methods are specifically summarized. Other theoretical methods like molecular mechanics and molecular dynamics are also briefly introduced.In Chapter 3 and Chapter 4, the modulation on optoelectronic properties of two core/shell nanomaterials(Si/SiO2 core/shell quantum dots and Si/C binary core/shell nanowires)is investigated,which have been widely used in optoelectronic field. Our calculation results demonstrate that the optoelectronic properties of Si/SiO2 core/shell quantum dots and Si/C binary core/shell nanowires show “bowing effect” against the core/shell materilas’ ratio, other than linear changes. The existence of bowing effect indicates that the electronic structure of core/shell nanostructure is always dominated by several competing factors.In Chapter 5 and Chapter 6, the potential applications of two semiconducting siligraphenes(g-SiC2 and g-SiC7) in energy and optoelectronic field are theoretically simulated. The g-SiC2 siligraphene shows good adsorption affinity to oxygen molecules due to its novel silicon/carbon alternately arranged lattice structure, which makes it efficient oxygen reduction reaction(ORR) catalyst in alkaline environment. The g-SiC7 siligraphene shows moderate band gap(1.13 eV) and superior light absorption to sunlight, and is promising as donor material in next-generation flexible optoelectronic devices(such as solar cells).Chapter 7 is the systematic investigations on the potential applications of novel nanographene TB8 C and its derivates for metal atom adsorption. The calculation results demonstrate that comparing with the pristine graphene, the curved structure of TB8 C nanographene leads to significant enhancement in adsorbing metal adatoms. The investigations on modification show that the modification of amino group on TB8 C further enhance its adsorption affinity to metal adatoms. By characterizing the bond order between metal adatom and nanographene, we conclude the relationship between the valence electron configuration of metal element and its bonding types. This investigation elucidates that the nanographene has great application potential for carrying the metal atoms(especially the alkali metal atoms).Finally, Chapter 8 summarizes the whole work and discusses the outlook for materials design in the carbon/silicon nanomaterials field.