| Summary: | 碩士 === 南臺科技大學 === 光電工程系 === 105 === Since the discovery of carbon nanotubes(CNTs), CNTs have attracted intensive interest on nanotechnology due their unique properties, such as high Young modulus, high conductivity, and high field emission efficiency at low turn-on voltage. Many potential applications use their unique properties, ex. silicon hetero-junction solar cells. Methods for the synthesis of CNTs include arc-discharge, laser vaporization, thermal chemical vapor deposition (CVD), plasma enhance chemical vapor deposition (PECVD) and electron cyclotron resonance CVD (ECR-CVD). In consideration of the advantage of high dissociation percentage of the precursor gases and high uniformity of plasma energy distribution, the ECR-CVD is adopted for this study.
In this study, multi-walled carbon nanotubes (MWNTs) were synthesized on a silicon substrate at relatively low temperature 500℃, using an ECR-CVD. Mixing gases of Methane (CH4) and Nitrogen (N2) were used as the carbon source and the plasma treated Ni film as the catalyst. Process parameters such as process time, microwave power, and gas flow were altered to optimize the properties of MWNTs on Si. The surface morphologies and microstructures of carbon nanotubes are examined by scanning electron microscopy (SEM).
The results show that ECR-CVD grown CNTs reveal vertically aligned character and the length of CNTs is varied from 0.3μm to 2.6μm.The density and uniformity of CNTs can be optimized using the plasma treated Ni catalyst under power of 440W. The signs of the Hall coefficients are negative, indicating that majority carriers are electrons in these films. CNTs/n-Si junction property depends on the density and length of CNTs. The ideality factor (n) of the best CNTs/n-Si junction is equal to one.
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