| In recent years, as a kind of revolutional nano material, carbon nanotube (CNT) has attracted lots scientists throughout the world with exceptional physical and chemical properties. Devices based on CNT such as CNT gas sensor, CNT-field effect transistor, CNT micro-transducer and CNT probe, have shown great application potential. In this dissertation, two essential assemble processes-dielectrophoresis (DEP) and pattern transferring- of fabricating CNT based sensor were studied and realized separately on CNT flow sensor.The pre-processes of CNT before using in sensor assembling include purification, cutting and dispersion. Reflux was used to remove most of the impurities in CNT. Acid oxidation was used to cut CNT and control the length of it. Dimethylformamide (DMF) was chosen to disperse CNT as a solvent and different surfactants were used to help CNT dispersing in water. For CNT aqueous suspension, the concentration of surfactant was important for the stability of CNT suspension.The mechanism of carbon nanotube sensing flowing liquid was studied partly by understanding the development of theoretical models and partly by calculating using density functional theory (DFT) based first-principles calculation program Dmol3. The adsorption energies of particles such as water molecular, sodium ion, hydrogen ion and chloride ion on CNT outside wall were calculated. The results showed that with the participation of positive ions in flow liquid, the flow-induced voltage of CNT can be improved compared to pure water.Subsequently, theoretical calculation and experimental research of DEP process was studied, and results showed it can be used to fabricate CNT sensors on silicon substrate. The theoretical calculation was carried out by COMSOL Multiphysics. The simulation of DEP process of CNT between two electrodes showed that the position and direction of CNT are determined by DEP force field distribution. Scanning electron microscope images of CNT with different DEP time illustrated the proof of simulation results. Induction heating was introduced to reduce contact resistance between CNT and electrode. The reduction depended on induction heating time and power. Simultaneously, the process of transferring patterned CNT films to polydimethylsiloxane (PDMS) to form CNT/PDMS composite thin film was studied experimentally. The process included lithography, filtration and plasma etching. CNT/PDMS composite thin film made by this method had uniformly dispersed CNT, and consequently had stable electrical properties indicating it can be used as sensor cell.Finally, the above two methods were used to fabricate CNT flow sensor separately, while one is based on silicon substrate and the other is based on PDMS substrate. The sensing characteristics of both these two CNT flow sensor were studied. The results showed that flow-induced voltage of CNT increases with the increasing of flow velocity and ion concentration of liquid, suggesting ions in liquid make more contribution to driving free electrons in CNT. This result was consistent with the calculation of adsorb energy. For CNT flow sensor made by DEP process, the flow-induced voltage also depended on the length and density of CNT films. While for CNT flow sensor made by patterned transfer process, the flow-induced voltage depended on the conductivity of composite thin film. However, the sensitivity of DEP made flow sensor was higher than composite flow sensor, because CNT was separated from flow liquid by PDMS chains in the later one. Interestingly, for both flow sensors, it was observed that the flow-induced voltage tends to saturate at flow velocity as low as 0.0008 m/s. Once free electrons in CNT were driven to move, the surface charge of CNT became negative and may influence the dynamics of water molecular and ions outside CNT wall. This could be the reason.Our studies have an important role for the design and manufacturing of CNT based sensors. Also, our results are very useful for further understanding of CNT flow sensing mechanism.
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