Preparation And Field Emission Of A Carbon Nanotube / Silicon Nested Arrays, Humidity Performance

Carbon nanotube (CNT) has drawn wide attention due to its potential application in fields of flat panel display, sensor, nano-device and SPM probe bring by its unique structures and properties since its discovery in 1991 by luijima. On one hand, large quantity research has been put on CNT as a cold cathode electron source due to its small tip radius of curvature, high aspect ratio, relatively low work function, high thermal conductivity and chemical stability. Up to date, however, field emission properties of CNT are far from theory estimated, such as a low emission site density and unstable electron emission. There also are numerous argues in the understanding of growing mechanism. Better the emission properties of CNT is an important step for industrialization. On the other hand, CNT has been highly expected as a novel sensing material because of its large sensing area and high chemical inertness. CNT-based resistive gas sensors demonstrate a high sensitivity and a high response rate in detecting NO₂, H₂S and NH₃ toxic gases, while only show a very low sensitivity to relative humidity (RH). At the same time, CNT-based capacitive humidity sensors posses a high sensitivity, but accompanied with a long response time and a nonlinear capacitive response with RH. Our group reported a novel silicon hierarchical structure, silicon nanoporous pillar array (Si-NPA), and based on which field emission cathode and humidity sensor with good field emission and sensing properties, respectively, were obtained. The good properties were mainly attributed to its unique structure and morphology. This thesis is try to integrate the advantages as emitters and humidity sensors of CNTs and Si-NPA as an effective substrate to probe the emission properties and humidity sensing properties of their component structure. A nest array of multiwalled carbon nanotube/silicon nanoporous pillar array (NACNT/Si-NPA) was synthesis by thermal chemical vapor deposition (CVD), and a full understanding of its growing mechanism, betterring its field emission properties and humidity sensor properties. The content and contribution are as follows:1. Synthesis a quasiperiods hierarchical structure of NACNT/Si-NPA, its microstructure was characterized and analyzed by SEM, TEM, Raman. NACNT/Si-NPA was fabricated by controlling the temperature and time on Si-NPA. An optimum condition was given through charactering its morphology and structure by field emission scanning electron microscope (FE-SEM) and high resolution transmission electron microscope (HRTEM). The influence of growing temperature on the quality of CNT was analyzed and the growing mechanism was deduced accordingly.2. Studied the growth mechanism of NACNT/Si-NPA synthesized by floating catalyst methods. The morphologies and components of NACNT/Si-NPA synthesized by different methods, such as catalyst-free, pre-immersion catalyst, and floating catalyst methods, were characterized by SEM, TEM and selected area electron diffraction (SAED). The CNTs were removed from NACNT/Si-NPA through physical method, and regrowth CNT on the CNT-removed substrate was conducted. The growing mechanism was analyzed thoroughly and a new growing mode was presented.3. Better the field emission characteristies of NACNT/Si-NPA. The field emission characteristies of NACNT/Si-NPA synthesized under all kind conditions were measured with special apparatus. All of the samples show a good emission properties with a low turn-on field, a big emission current density at a relative low field. A multi-step emission mechanism was presented. The growing condition of NACNT/Si-NPA with best emission properties was obtained. It's far better than CNT grown on flat substrate. This work will give instruction on the practice application of CNT to a certain extent.4. Tested the humidity properties of NACNT/Si-NPA and obtained good results. Employ its peculiar electrical properties exhibited in the presence of different gases and the structure advantage, the humidity properties of NACNT/Si-NPA synthesized under different condition were studied. Ther esults show that as-prepared NACNT/Si-NPA could exhibit high sensitivity, short response/recovery times and good measurement reproducibility. The resistive humidity sensing material of NACNT/Si-NPA has a higher sensivity, a better linear response contrast with others reports. The common problem, nonlinear capacitance-RH curve, can be overcome through replacing the longitudinal coordinates with the logarithm of capacitance for capacitive type NACNT/Si-NPA sensor, which will provide a way for better using capacitive sensors. These excellent performances of NACNT/Si-NPA are attributed to the unique surface structure, morphology and chemical inertness of NACNT/Si-NPA. The humidity sensing mechanism of NACNT/Si-NPA analysized from the point of view of band and a mode was proposed.