Design And Physical Properties Of Functional Materials Based On Silicon Dioxide

Due to the wide application prospect in the field of functional materials,such as fused silica,bismuth-doped silica optical fiber and metal-oxide interfaces,silicon dioxide has received extensive attention from researchers.Based on silicon dioxide functional materials,silicon-dioxide-based models with different structures were designed.And their basic physical properties,luminescence characteristics and dielectric breakdown properties were investigated systematically by combining the first-principles method.This thesis will provide a theoretical basis for silicon dioxide in the preparation of functional materials and device applications.The main research contents of the thesis include:(1)Research on the basic physical properties of oxygen-deficiency-related defects in fused silica.Through designing the ODC(?)defect models,we found that as the Si-Si bond becomes longer,the formation energy of ODC(?)defects gradually increases,and the corresponding optical absorption peak gradually splits into two peaks and shifts to both sides.We also designed the ODC(?)defect aggregation models with different member rings and found that ODC(?)defect aggregation is more likely to occur in the 5-membered rings.The adsorption characteristics of surface E' defects were also investigated.The results showed that F atoms are easier to be trapped by surface E' defects than Cl atoms,and the introduction of F/Cl atoms will lead to the disappearing of defect states in the band gap.(2)Research on the luminescence characteristics of low-valent bismuth in Bi-doped silica optical fiber.The trivalent bismuth models with different member rings were designed,and we found that the broad spectral range from ultraviolet to visible light is caused by a combination of trivalent bismuth ions and member ring structures.We also designed and investigated three different monovalent bismuth structures.We found that the luminescence near 1492 nm is caused by SiOBi configuration,and the luminescence at 1147 nm and 1403 nm is mainly related to the interstitial Bi2O configuration.The reaction paths from trivalent bismuth to divalent bismuth defect center in different member rings were also investigated.It can also be found that the near-infrared luminescence at 1252 nm,1306-1313 nm,1574 nm and 1600 nm may be caused by the bivalent bismuth defect center.(3)Research on the dielectric breakdown properties of the aluminium/silicon-dioxide interface.By constructing three different Al/SiO2 interface models,we found that the O interface model is the ideal anti-dielectric-breakdown interface model with higher electrostatic potential offset,larger virtual oxide thinning thickness and lower electron potential barrier height.The conversion paths within the three interface models were investigated.The Si interface model can convert into the O interface model,and the O interface model can convert into the SiO interface model.The conversion of SiO interface model to Si interface and O interface model requires less energy.The main innovations of the thesis include:(1)Linear and aggregation characteristics of oxygen-deficiency-related defects in fused silica:We discovered that there is a linear relationship between the formation energy and Si-Si bond length of ODC(?)defects,and revealed the aggregation characteristics of ODC(?)defects with different member rings.These results provide a theoretical basis for the preparation of fused silica related devices.(2)Luminescence mechanism of low-valent bismuth in Bi-doped silica optical fiber:We found a correlation between monovalent bismuth and divalent bismuth defect centers and near-infrared luminescence of Bi-doped silica optical fiber.This work clarifies the luminescence mechanism of low-valent bismuth and provides a theoretical basis for the preparation of high performance Bi-doped silica optical fiber.(3)Dielectric breakdown mechanism of Al/SiO2 interface:The results showed that the O interface model has good resistance to dielectric breakdown,and revealed the mutual conversion characteristics among the three interface models.The research provides theoretical guidance for the development of an anti-dielectric-breakdown metal oxide interface.