A study of the growth and fabrication of carbon nanotube arrays in microfluidic channels and their application in micro-particle separation for bio-sensing devices

• Main Author: Mathur, Ashish
• Published: Ulster University 2011
• Subjects: 670
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.535153

This thesis will address the controlled growth of carbon nanotubes (CNTs) using two different methods i.e. (1) Microwave Enhanced Plasma Chemical Vapour Deposition (ME-PECVD) and (2) Thermal CVD. The micro-structural and compositional analysis of the samples were investigated by various techniques such as the Scanning Electron Microscopy (SEM), Raman spectroscopy, High Resolution Transmission Electron Microscopy (HRTEM), X-ray Diffraction (XRD), and static contact angle studies. Electric field emission properties were also studied. Fabrication of microfluidic channels and the integration of CNTs in microfluidic channels is also investigated. In this work, the effect of catalyst thickness and growth-time of carbon nanotubes (CNTs) by microwave plasma chemical vapour deposition (MPCVD) technique was investigated. Also the role of a thin buffer layer (Aluminium in this case) under the catalyst was also explored. CNTs were grown by a thermal chemical vapour deposition (TCVD) method and the effect of CNT growth on various substrates, using TCVD process, was studied. CNTs were also grown in various patterns via the two different techniques as mentioned above. The effect of pattern-size on the growth of vertically aligned CNT pillars was investigated. The catalyst patterns were made using two commonly used techniques (i) maskless photolithography (ii) nano/micro sphere lithography. The effect of patterns on CNTs field emission and micro-structural properties was also studied. These patterns were made on silicon as well as on quartz and also integrated in microfluidic channels for micro-particle filtration application. Due to their hydrophobic nature, CNTs are the least preferred material as far as contact with liquid is concerned. In this work, CNTs were functionalised using two different methods, with a view of keeping their vertical alignment intact and reducing the contact angle. The vertically aligned MWCNTs synthesised by MPECVD and TCVD were treated in a low power oxygen plasma, which resulted in (i) lower contact angle with vertical alignment intact (ii) the efficient removal of metal caps at the nanotube tips and (iii) incorporation of oxygen into the CNTs making them better field emitter. These experiments on the CNTs revealed O2 plasma functionalization, as a novel, non toxic, technique that can be used for the purifying, functionalization and tip opening of the CNTs. The XPS and Raman validated the plasma cleaning and defect generation in the CNTs, while, XPS, SEM and Raman showed the efficient removal of metal catalyst from the nanotube tips in the vertically aligned MWCNTs. Another area explored in this research work was the fabrication of microfluidic channels. A commonly used photolithographic technique was used for the micro channel fabrication using SU8 as a photoresist on silicon/glass/quartz. Also a hot-embossing technique was used to fabricate polymeric micro-channels. The integration of CNTs in microfluidic channels, in order to use them as micro-particle filters, was also studied. Due to the lower glass transition temperature of polymers a novel technique was needed to transfer vertically aligned CNTs onto the polymers for microfluidic based filters. In this work a hot-embossing technique was used to transfer the VACNTs onto the microfluidic channels. It was found that this process gives complete transfer of CNTs from the substrate to the polymeric channels. Finally, a CNT based microfluidic device was fabricated using lithographic and hot embossing techniques. Optimised device fabrication conditions and the role of CNTs as a micro particle filter is investigated.