Growth and Characteristics of ZnO Nanostructures
Date Issued
2004
Date
2004
Author(s)
Hsu, Ning-Erh
DOI
en-US
Abstract
In this thesis, ZnO nanostructures (such as nanowires, nanorods and nanosheets) were grown at about 1000℃ by using gold as catalyst via Vapor-Liquid-Solid (VLS) mechanism. These ZnO nanostructures were examined by a field-emission scanning electron microscope (SEM). The substrates used were sapphire with the a plane and silicon with the (100) and (111) plane. The experimental result shows that none-oriented ZnO nanowires or nanosheets were grown on silicon substrates, and nanowires along the c axis or the three a axes of ZnO crystal were grown on the a plane sapphire substrates. Some samples even possess that most of the orientation of nanowires is along the c axis (i.e. standing nanorods).
Photoluminescence (PL) spectra of ZnO nanowires and nanosheets were measured using a He-Cd laser (325 nm) as the excitation source. Two emission bands were observed. One is the ultraviolet (UV) band with peak position at about 380 nm caused by the transition of excitons, and the other is the green band commonly referred to as a deep-level or trap-state emission caused by the defects of the crystal. At room temperature, nanosheets shows better optical property than nanowires or nanorods, that is to say, nanosheets possess larger intensity of the UV band than that of the green band.
In addition, we found that the PL emission of ZnO nanorods is polarized. The intensity of both the UV emission and the green emission varies with the polarization angle by the relation of square cosine function. The intensity of UV emission has its maximum along the c-axis of ZnO crystal. However, intensity of green emission has its minimum in this direction. Namely, two intensity curves are 90o out-of-phase. The polarization of the UV band is attributed to the anisotropy of the one dimensional structure of nanorods. However, the polarization of the green emission can deduce an interesting result that the green emission mostly occurs at the surface defects of the nanorods.
The property that the UV emission and the green emission are polarized out of phase provides a simple way to verify that the defect emission occurs mostly at the surface defects of ZnO nanorods.
Subjects
成長
奈米結構
氧化鋅
奈米線
奈米
nano-
growth
Zinc Oxid
ZnO
nanostructure
nanowire
Type
thesis
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