Controllable Preparation And Physical-Mechanical Properties Of Boron Nanostructures On Nickel Foils Via Chemical Vapor Deposition

The special electronic structure of boron with seriously deficient electrons makes it have a very complicated bonding mechanism,and tends to form a complex polyhedral structure and have complex and peculiar properties,and thus has attracted extensive attention in the scientific community.Although a large number of theoretical studies on boron nanostructures have been done,however,experimental investigation especially in two-dimensional B-nanostructures is a newly emerging field.In this paper,chemical vapor deposition is used to directly control low-dimensional B nanostructures on the nickel substrate under the condition of H₂ and Ar gases.Two dimensional?2D?boron nanostructures such as a novel direct band gap semiconductor B nanosheets with face-centered cubic structure,?-T phase B nanowires,and a series of nano-cubic boron sheets were simulated by first-principles calculations.The theoretical models and the related experimental results lay a solid foundation for the development of novel B allotropes.The research contents and innovations of this thesis are as follows:?1?Preparation,characterization and photoelectric properties of boron nanosheets via chemical vapor deposition.Firstly,we have successfully prepared a direct band-gap semiconductor B nanosheet with a pseudo face-centered cubic structure on a nickel foil via CVD.In the mixed atmosphere of H₂ and Ar at 500 ?,a new face-centered cubic boron nanosheet with regular shape can be prepared.Secondly,the Ni foil substrate was etched away by FeCl₃ solution to successfully transfer the B nanosheets onto any target substrates.Finally,the structure and performance were characterized.HRTEM results show that the nanosheet is a new phase of boron with the pseudo face-centered cubic structure,in good agreement with the theoretically simulated crystal structure.The AFM results show that the B nanosheets are only 6.94 nm in thick.Cathodoluminescence and photoluminescence mearements showed that the B nanosheets prepared under this condition were a semiconductor with a band gap of 2.4 eV.This is the first time to experimentally report the 2D semiconductor B nanosheets with pseudo face-centered cubic structure,which greatly enrichs the crystal structure of boron.?2?Theoretical calculation of the pseudo face-centered cubic boron nanosheets.Using first-principles calculations software Materials Studio,we have constructed a series of two-dimensional boron nanosheet structures composed of icosahedral B₁₂ as the basic unit.During the procedure,a facecentered cubic lattice with a side length of 0.8 nm,and fill it with 4 B₁₂ spheres has been established.We have obtained 15 corresponding stable stick models after geometry optimization,where the appropriate positions of the crystal lattice were selected by deleting individual B atoms in the B₁₂ sphere or adding B atoms among the B₁₂ spheres.In these models,we have found a theoretical model corresponding to the crystal structure and electronic structure of the boron nanosheets in Chapter 2.?3?Preparation,characterization and growth mechanism of boron nanowires via chemical vapor deposition.We have directly prepared a series of boron nanowires via CVD using nickel as the substrate.A series of B nanowires were characterized by SEM,TEM and EDX,respectively.It can be found that the optimum temperature and reaction time for preparing high-quality boron nanowires are 700 ? and 1 h,respectively.Furthermore,the growth mechanism of B nanowires is also revealed.