Synthesis, characterization and application of Si nanotips and carbon nanotubes

• Main Authors: Ya-Ping Hsieh, 謝雅萍
• Other Authors: 梁啟德
• Format: Others
• Language: en_US
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/00565657100427830300

博士 === 臺灣大學 === 物理研究所 === 98 === In this thesis several aspects of nanostructured materials are investigated. These materials, defined by having one or more dimensions at the nanometer scale, have exciting properties that link them to the microscopic realm of atoms and molecules. At the same time their application has and will have a gigantic impact on our future in fields as diverse as energy harvesting and health. A broad perspective on these materials by describing several fields of intensive current research will be given in this thesis and the emphasis will be put on three issues: 1. Synthesis of Single-walled carbon nanotubes thin films via Electrostatic spray-assisted chemical vapor deposition In this topic, a detailed study on growth of carbon nanotubes (CNTs) will be presented. Electrostatic-spray assisted chemical vapor deposition is described as a way to directly deposit single-walled nanotube (SWNT) thin films on a substrate. Through a strong electrical field, the catalyst solution was finely dispersed and injected into the heated reaction zone (950-1100 °C) during the growth. It was also found that under optimized growth conditions, the deposited materials were almost exclusively SWNTs and only contain small amounts of impurities. The growths at different temperatures result in nanotubes of different morphology and length. The location of the SWNTs’ deposition is found to be affected by the nanotube length and the growth temperature and this behavior is explained by considering different forces acting on the floating nanotubes inside the furnace. These results could provide a route of sorting floating SWNTs for electronics applications. 2. Analysis of Raman resonance windows of individual single-walled carbon nanotubes The single walled carbon nanotubes grown by the previously described ESACVD process, were investigated by Raman spectroscopy on the individual nanotube level to extract differences in the physical properties for different chirality nanotubes. Raman spectra of isolated SWNTs were obtained for a wide range of laser excitation energies to study the resonance window of the Raman RBM feature for members of (2n+m) families. A chiral angle (θ) dependence of the resonance window width (Γ) was observed that is much stronger than the diameter dependence. A strong correlation between the θ dependence in Γ and the D-band intensity was observed. The analysis in this thesis suggests that defect scattering could be an important source of electron relaxation affecting the resonance window width. 3. Application of ZnO/Si-nanotips as Light Emitting Diodes. This research represents the application part of the nanostructured material study in this thesis. A new and general approach to achieving efficient electrically-driven light emission from a Si-based nano p-n junction array will be introduced. By a single-step self-masked dry etching process, a wafer-scale array of p-type silicon nanotips were formed, which is compatible with current semiconductor technologies. On top of the silicon nanotip array, a layer of n-type ZnO film was deposited by pulsed laser deposition. The excellent quality of the ZnO film is characterized by both the narrow linewidth in cathodoluminescence spectra and the appearance of multi-phonon Raman spectra up to the 4th order. The turn-on voltage of our ZnO/Si nanotip array is found to be only ~2.4 V, which is 2 times smaller than its thin film counterpart. Moreover, electroluminescence (EL) from the ZnO/Si nanotips array light emitting diode (LED) has been demonstrated. The results shown in this research could open up new possibilities to integrate silicon-based optoelectronic devices, such as highly efficient LEDs, compatible with standard Si ultra-large-scale integrated technology.