The low temperature synthesis process of verticallyaligned carbon nanotubes and the transfer process for applications in soft electronics and periodic arrays: field emission device and light grating

• Main Authors: Tsai, Tsung-Yen, 蔡宗岩
• Other Authors: Tai, Nyan-Hwa
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/62221769250902314784

博士 === 國立清華大學 === 材料科學工程學系 === 97 === In this work, Ni nanopowder mixed with commercial Ag-paste was screen-printed on glass substrate, and then growth of carbon nanotubes (CNTs) was performed in a chemical vapour deposition (CVD) chamber at 500 °C for fabricating field emitters. The proper concentration of catalyst enables to the successful production of cathode and enhances the field emission properties. However, higher catalyst concentration results in the cathode peeling off due to the volume expansion during the growth of CNT and lower catalyst concentration results of decrease in the emission sites due to the poor CNT coverage. The growth of vertically aligned CNT (VA-CNT) on glass substrate at a low temperature of 450°C was demonstrated using Co/Ti bimetallic catalyst. It was found that the ratio of Co/Ti and the selection of substrate influence the CNT length; CNTs can not grow on glass substrate at lower temperature when pure Co layer or catalyst layer with excess Ti content was used. Si substrate reacts easily with catalyst under higher temperature (700°C), which decreases the catalyst activity and fails to grow VA-CNT. To overcome this problem, a two-step process was proposed which can prevent the catalyst from poisoning during CNT synthesis. Moreover, in order to grow VA-CNT array on the surface of micro-scale periodic structures, the catalyst was coated on the array composed of PS spheres with different sizes. It was found that the Co/Ti catalyst system with the ratio of 3 nm/3 nm in thickness could be used in micro-scale periodic structures. The study of transfer process can be categorized into two sorts, one is for hard substrate and the other is for soft substrate. For transferring complicated VA-CNT pattern with a height higher than 20 �慆 onto a hard substrate, silver paste was adopted as transfer medium. After the transfer process, the CNTs with open-end structure fit them to fabricate the field emitter for the high current density applications. A direct transfer method was developed for transferring VA-CNT with height of about 5 �慆 onto soft substrate. After the transfer process, the VA-CNTs maintained their initial orientation in the designed pattern and showed the pattern even the line width is about 5 �慆. The flexible device showed excellent emission performance even if under bending condition and exhibited the function of strain gauge for bending. A self-assembly nano sphere lithography (NSL) mask for the fabrication of periodic CNT arrays was improved by adopting a catalyst-poisoning layer. Using this method, the uniformity of the CNT array could be improved by preventing the negative influence of arrangement defects in self-assembled monolayers. CNT array exhibited the diffraction of visible light due to the size and period within the wavelength scale. In addition, the process with Si mold for patterning a grating was capable of transferring CNT array onto flexible substrate. The periodic pattern could be in the scale of 350 nm. The structure period and spectra analysis match the diffraction theory. The vision from dark to iridescence was obtained by using the CNT grating.