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The Growth and Field Emission Properties Research on Tin Oxide Nanostructures

Author: LiZuo
Tutor: WangJinBin
School: Xiangtan University
Course: Physical Electronics
Keywords: SnO2 Oxygen Vacancy Field Emission Catalyst Growth Mechanism
CLC: TB383.1
Type: Master's thesis
Year: 2009
Downloads: 169
Quote: 1
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Abstract


As a representative n-type semiconductor material with direct large energy gap and negative electron affinity, SnO2 has excellent physical and chemical properties, and was widely used in solar cell, high temperature electronic devices, gas sensors, transparent conductive glass, flat panel display and other fields. Now, SnO2 nanomaterials have been a good potential materials applied in field emission flat panel display. In this paper, different SnO2 nanostructures were prepared by chemical vapor deposition （CVD） process with metallic catalyst-assistance. We discussed the effects of the catalyst on the growth mechanism of SnO2 nanostructures, studied the field emission properties of SnO2 nanowires and nanobelts, and focused on the effects of the post-annealing process in oxygen on the field emission of SnO2 nanowires.Compact SnO2 nanowires had been successfully prepared by CVD on silicon substrate with 7nm thick Au, and annealed in oxygen at high temperature. We researched the effect of post-annealing process in oxygen at high temperature on the cathodoluminescence and field emission properties of SnO2 nanowires. We researched the microstrucutre and the surface morphology using X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, high-resolution transmission electron microscopy （HR-TEM）, selected area electron diffraction （SADE） and energy dispersive X-ray detector （EDX）.All the diffraction peaks in the pattern can be indexed as a crystal structure of the tetragonal rutile SnO2 structure and the crystallization of the nanowires is gradually improved by a post-annealing procedure in oxygen. The length of the nanowires is more than 10μm and the width is in the range of 30-95 nm. The HR-TEM image of the selected region indicates that the entire nanowire is a single crystal. Energy dispersive X-ray spectroscopy （EDX） analysis reveals the presence of Sn and O, and the atomic ratio of O to Sn in SnO2 nanowires increases gradually with the increment of annealing temperature. It indicates that there are many oxygen vacancies in the as-grown SnO2 nanowires which can be compensated by post-annealing in oxygen.Compact SnO2 nanobelts had been successfully prepared by CVD on silicon substrate with 10nm thick Au. We researched the microstrucutre and the surface morphology using X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, high-resolution transmission electron microscopy （HR-TEM）, selected area electron diffraction （SADE） and energy dispersive X-ray detector （EDX）. All the diffraction peaks in the pattern can be indexed as a crystal structure of the tetragonal rutile SnO2 structure. The length of the nanobelts is more than 20μm and the width is in the range of 95254nm. The HR-TEM image of the selected region indicates that the entire nanobelt is a single crystal. Energy dispersive x-ray spectroscopy （EDX） analysis shows the presence of Sn and O, and reveals that there are some oxygen vacancies in the as-grown SnO2 nanobelts. The field emission properties of SnO2 nanobelts are not as good as SnO2 nanowires, due to its smaller length-diameter ratio and smaller field emission enhancement factor.We studied the function of catalyst on the nanostrucure morphology and growth mechanism. It is too difficult to grow nanobelts with nothing on Si substrate. And, it is confirmed the validity of vapor-liquid-solid mechanism; Sn is a self-catalyst; the growth is a self-assembly, autocatalytic growth process. It is hard to control the morphology grown with Pt on Si substrate. It is easy to grown and control the nanostructrue prepared with Au on Si substrate. The growth mechanism of the as-grown nanostructures with Pt and Au metallic catalyst-assisted in our study is suggested to be typical vapor-liquid-solid processes. The results showed that the catalyst play a very important role in the preparation of the nanostrucutre of SnO2. It is easy to grow single crystal SnO2 nanostructure with the catalyst. The width of the nanostructure is follwed with the thick of the catalyst. We can control the location and scale of SnO2 nanostructures by control the distribution and thickness of the catalyst on the substrate.The review on the study of growth mechanism and field emission properties of SnO2 nanostructures can help learn the development of the study, which can promote the study in this field.

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