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Microstructure and Properties of Silicon Based Nano-composite Thin Films by CVD and Research of Novel Antireflecting Energy Saving Coating Glass

Author: LiuFeng
Tutor: HanGaoRong
School: Zhejiang University
Course: Materials Science
Keywords: nano-composite thin film post-heating microstructure photoluminescence gradient films modification of the microstructure anti-reflection
CLC: TB43
Type: Master's thesis
Year: 2002
Downloads: 163
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Abstract


In this thesis, the history, structure .preparation method and basic properties of nano-composite materials and photoluminescence of nanocrystalline silicon have been summarized. Research of the novel antireflecting energy saving coating glass has also been presented.The Si/SiC composite films are prepared with SiHt and €2^4 as the source gas by atmosphere pressure chemical vapor deposition (APCVD). Then, by annealing, the Si/SiC/SiCh nano-composite films are prepared. The influence of the post-heating on the microstructure of the films has systematically been studied by the means of the measurements of HREM. The nano-crystals are found embedded in the amorphous matrix in the unannealed sample and the crystallinity is not high. A large amount of nano-crystals are found in the film when the sample was annealed for one hour at 500 癈 with the crystallinity being increased to 50%. At the same time, the crystals in the film continue to grow. The single Si crystals with the size of about 200nm are also found in the film. When the temperature of the post-heating is increased to 600 癈, the crystallinity of the film is also increased to 60%~70%. Two exceptional structures appear in the film. They are Concentric ring of Si and Hollow ring of C. The former is composed of three parts: the outer belt, the medium and the heart. The latter structure is composed of polycrystalline graphite in fact. A large amount of SiC>2 single crystals with the size of lOnm appears in the film when the time of the post-heating is increased to five hours.The Si nano-wires are found in the sample annealed for one hour at 500 "C. It can be explained by the mechanism of metal inducement.The photoluminescence of the thin films without post heating is weak. Only one luminescence band is found nearby 473nm.two luminescence bands are found after post heating, nearby 493nm and 368nm respectively. The intensity of the luminescence bands increase little by little when the temperature and the time of post heating continues to increase. The model of the photoluminescence of the nanocrystalline silicon can explain the result.The optical property of the thin films has systematically been studied. The gradient films and the modification of the microstructure can be realized by the post-heating. Then the novel antireflecting energy saving coating glass is achieved. It is also found When the temperature and time of the post-heating increases, the average reflectivity will decrease and the average transmission will increase. The average of reflectance and transmission of the coating glass is 27.7% and 33.0%, respectively after the thin film has been annealed for one hour at 500癈.

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