Manipulation Of Nanomaterials By Dielectrophoresis And Its Application In Micro/nanosensor Fields

With the development of micro/nanotechnology, more and more unique properties of micro/nanomaterials are continuing to be researched and recognized. The nano materials are regarded as the potential building block elements to construct the nanoelectronic circuits and the high performance micro/nanosensors. In these applications, normally, the nanomaterials as the building block elements should be put into the predesigned position of the micro/nanostructures. For instance, when using the nanomaterials as sensitive device to fabricate the electrical sensor, it is generally to bridge the sensitive material between the pairs of electrodes, so as to transfer the change of the sensing material into the useful electrical signals conveniently. Hence, how to position the materials selectively is the primary problem needed to be solved.In this thesis, the manipulation of nanostructured zinc oxide, a novel semiconductor material, by dielectrophoresis had been investigated. With the aids of millimeter gap sized pairs of electrodes and micrometer gap sized pairs of electrodes, the factors which can affect the manipulation had been studied. The humidity sensing characteristics of nanostructured zinc oxide in these structures also had been studied. The results obtained can provide the guidance for the future study of novel nanostructured sensors. The main works and the results are listed as below:The ZnO nanorods were synthesized by the aqueous thermal decomposition technique. The prepared ZnO nanostructures were characterized by X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) to obtain the information on the structural and morphological properties, etc.. The as-received ZnO nanostructures were used for the dielectrophoretic manipulation.The dielectrophoretic manipulation of the silicon dioxide particles with millimeter gap sized pairs of electrodes were investigated in order to provide the principle information. The influence factors of the dielectrophoretic maunipulation such as the voltage and the frequency of the applied signals were studied. The novel impedance humidity sensor were constructed by dielectrophoretically putting the the aligned nanostructured ZnO into the electrode gaps as the humidity sensing element. The electrical impdance changing with the humidity level had been studied. The study indicated that the humidity sensor developed has the high sensitivity and the good reproducibility within the humidity level ranging from 30% to 80%RH. It is also a good fundamental preparation for future minimization.The dielectrophoretic manipulations of the nanostructured ZnO with micrometer gap sized pairs of electrodes were investigated. The electrodes with different configurations were fabricated by standard IC process. The SEM pictures have been used to examine and evaluate the manipulation results. The influences of the configurations of electrodes, the frequency and the voltage of applied external signals, the concentrations of the nanostructured ZnO suspensions on the dielectrophoretic manipulation effect have been investigated. We succeeded in manipulating ZnO particles along the electric field and depositing them across the electrode gaps. A novel capacitive humidity sensor based on nanostructured ZnO has been researched by detecting the variations of the dielectric constant of ZnO, dielectrophoretically aligned in the electrode gap, changing with the humidity. The sensing properties, such as the sensitivity, the reproducibility, the stability and etc. were studied. Our study showed that the ZnO nanorods are also the good sensing materials and the sensor based on the ZnO nanoparticles is potential for humidity detection.Since the nanostructured ZnO humidity sensors based on dielectropheresis developed have the properties such as the high sensitivity, the fast response time and the digital output, a prototype of wireless sensor system based on the nanostructured ZnO humidity sensor was also investigated. This sensor system mainly consisted of two parts: the nanostructured ZnO humidity sensors which can sense the change of humidity levels and the GSM Modem which can send the data of humidity detected by short message to customer's mobile phone. The real-time detection of humidity is realized. The developed wireless sensor system can be used as both the probe for real-time humidity detection and the node for the wireless sensor network.