Controlled Fabrication Of Carbon Nanotube Architectures By Chemical Vapor Deposition

Ordered nano-structured materials with nanomaterials as the units have attracted much attention in recent years because of their peculiar properties such as the intrinsic effect,the nanoscale effect and the combination induced new functions.Carbon nanotubes(CNTs) arranged into well-defined configurations to build integrated systems can help to display their novel and enhanced properties.Owing to the perfect mechanical,electrical and thermal performances,CNT architectures with regular geometry structures have exhibited promising applications in sensors,nano-electronics and nano-devices.Therefore,developing various approaches for the assembly of highly organized CNT architectures and investigating their general properties are stongly desirable in CNT research field.In the present thesis,CNT architectures with regular geometry structures have been achieved using different synthetic strategies by the floating catalytic chemical vapor deposition(FC-CVD) with ferrocene as catalyst precursors and cyclohexane as carbon sources. The morphologies and structures of the obtained samples have been characterized by scanning electron microscope(SEM),transmission electron microscope(TEM) and Raman spectra,etc. The possible mechanisms of the assembly of CNT architectures have been proposed and discussed in terms of different synthetic strategies.The wettability and electrochemical behavior of the CNT architectures obtained are also explored.Some progresses in the thesis are briefly summarized as follows.A series of aligned CNT patterns with regular geometry structures have been fabriacted using the two-dimensional(2D) template method.Patternings of Pt/SiO₂ and Si/SiO₂ substrates are prepared by photolithography,and aligned CNTs grow readily on SiO₂ surface guided by the selective deposition of catalysts on it rather than on Pt or Si areas during the subsequent CVD process.By strictly inheriting the 2D topography of the SiO₂ templates,a wide variety of 3D organized nanotube structures have been built in a well-controlled mode. Furthermore,a new approach with micro-sized Zn crystals as sacrificial template for the assembly of CNTs,as well as the layer by layer(LBL) growth of CNTs is investigated. Foam-like micropatterns consisted of CNTs have been realized by using the capillarity as the driving force combined with LBL growth of CNTs.With the CNT patterns grown on the SiO₂ templates as source materials,aligned CNT arrays can be transformed into zipped foam-like structrues after a water-wetting process.The combination of the capillarity and the CNT multi-layer growth has provided a versatile method for the construction of various complex CNT architectures based on different interaction between CNTs and the underlying substrate.The principle of capillarity-assisted self-assembly of CNTs is discussed in detail.Well-defined carbon polyhedrons with hierarchical structures made of in situ formed CNTs have been obtained inside space-confined microchannels.Microchannels which can be opened during CNT growth are created by two pieces of Au/SiO₂ substrates face-to-face assembled.The CNT polyhedrons display facetd morphologies and hollow internal structures. It is revealled that the bottom-up growth mechanism is involed in the assembly of the CNT polyhedrons by tracking the growth of the polyhedrons in different channels.Aligned micro-sized carbon tubes with CNTs formed in situ act as the basic buliding blocks have been synthesized on the silicon substrate in the presence of weak oxidizer(H₂O or CO₂).It belongs to a multiple self-assembly process and the concentration of catatlysts coming from the thermal decomposition of ferrocene plays the critical role.The weak oxidizer helps to remove amorphous carbon on the surface of catalyst to maintain its catalytic activity and life-span,consequently increase the growth rate of CNTs.The wettability of some typical CNT architectures obtained above and their application as electrode in the electroanalysis have been investigated.It is revealed that the CNT architectures possess a super-hydrophobic property and their wettabilities have a close relationship with their assembly.Electrochemical detection of homocysteine and dopamine using CNT patterns as the electrodes is also explored,further work is needed and on-going in this field.