Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemistry

Supervisor

Tsun-Kong Sham

Abstract

One dimensional nanomaterials have attracted extensive attention in recent years due to their superior electrical, optical, mechanical and chemical properties compared to their bulk counterparts. In this thesis, electronic structure and optical properties of three types of nanomaterials are investigated using synchrotron based X-ray absorption spectroscopy: X-ray absorption fine structure (XAFS) and X-ray excited optical luminescence (XEOL).

Si nanowire arrays are synthesized using electroless chemical etching, and coated with platinum and gold nanoparticles. The interaction between metal nanoparticles and the nanowire substrate is investigated using X-ray absorption near-edge structure (XANES). The luminescence properties of thermally oxidized Si nanostructures, such as Si nanowires, porous Si nanowires, and porous Si are comparatively studied. Using XEOL in combination with XANES, luminescence from defect centers in SiO2 and from Si/SiO2 interface can be distinguished. Electronic structure and luminescence of silicon carbide micro- and nanostructures of different crystal structures (polytypes) are investigated. Although hexagonal and cubic SiC have similar electronic structures locally, they exhibit different luminescence properties. It is found that all SiC samples have a same defect emission regardless of crystal size and structure. Additional luminescence bands are observed when oxide is present. Cubic SiC has two luminescence bands, originated from SiC and surface native SiO2, respectively. SiC nanowires also exhibit quantum confined band gap luminescence. As for boron nitride nanotubes, the presence of oxygen atoms in BN lattice alters the luminescence significantly by introducing a new defect center. The presence of oxygen impurities results in an intense signal revealed by XANES which is associated with B-O bonding, but no noticeable difference is seen in XANES at N site.


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