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Study On NO2 Gas-sensing LB Films And Microstructure Sensor

Posted on:2002-06-16Degree:DoctorType:Dissertation
Country:ChinaCandidate:D XieFull Text:PDF
GTID:1118360032453766Subject:Materials Physics and Chemistry
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With the development of Microelectro-mechanical Systems(MEMS) and microsensors, chemical sensors prepared by ultrathin film technology have been drawn more and more attention in recent years. The dissertation focus on the design and preparation of device structure for NO2 gas sensor, the fabrication and structural characterization of LB films, the gas-sensing properties and gas-sensing mechanism. The main results are as follows: 1. Based on the conventional MOSFET, two kinds of novel gas sensors have been fabricated for the first time. One is a chemical field-effect transistor (ChemFET) gas-sensing device with LB film deposited on the gate area of MOSFET replacing the gate metal; another is a charge-flow transistor (CFT) in the gap area of which the multilayer LB film was filled. And an array of four interdigitated CFTs has been fabricated as s set of devices which forms a simple microsensor. 2. LB films with different number of layers using polyaniline(PAN), copper phthalocyanine((i-PrO)4CuPc) and sandwich-like bis[2,3 ,9, 10,16,17,23,24- octakis(octyloxy)phthalocyaninato] rare earth complexes ? RE[Pc(0C3H17)3]( REEr, Pr, Sm, Tb) as film-forming materials have been prepared. The behavior of monolayers on the interface of air-water has been studied, especially the film-forming behavior and the compression-recovery behavior of pressure-area(7t-A) curve of RE[Pc(0C3H17)8]. It is found that Sm[Pc(OC8H17)8] is the most available for forming LB films among the six materials. The best film- forming condition is: mixing Sm[Pc(0C8H17)8j with octadecano(OA) at 1:3 molar ratio, the pH value and temperature of subphase is 6.2 and 25.0 respectively, the compression speed is 3mm/mm, the film-lifting speed is 2mm/mm, transfer ratio is close to 1.0. 3. These films have been characterized by ultraviolet-visible(UV-Vis) spectroscopy, X-ray photoelectron spectroscopy(XPS), transmission electron microscopy(TEM), atomic force microscopy(AFM), small angle X-ray spectroscopy(SAXS) and electrochemical cyclic voltammetry. The experimental III results show that: (1) LB films are uniform and solid, but it is easy to collapse at higher film pressure, (2) Multilayer LB films process sandwich structure and long- space orderliness, and the phenomenon of crystallization in the process of forming RE[Pc(0C8H17)8] LB films, (3)The thickness of RE[Pc(0C8H17)8] monolayer is about 50?0A, (4)During the formation of RE[Pc(0C8H17)8] multilayers, molecular arrangement is inclinable to the substrate, the angle is about 25o~~3Oo. 4. The gas-sensing properties of LB film based NO2 gas sensors fabricated with different materials(PAN, (i-P~O)4CuPc, RE[Pc(0C8H11)8), different film thickness and different device structures(planar microelectrods, ChemFET, CFT) have been studied in detail. The results show that Sm[Pc(0C8H17)8j has the best gas- sensing properties than others. The thinner the LB film or the higher the concentration of NO2 gas, the faster the response speed becomes. LB film based ChemFET and CFT show higher sensitivity and stability. The detection range of NO2 gas is O棐lOOppm, the response time to 2Oppm NO2 is shorter than 2Oseconds. 5. The gas-sensing mechanism of polyaniline and phthalocyanine is investigated. And the gas-sensing property and gas-sensing mechanism of RE[Pc(0C3H17)8] is studied by XPS for the first time. The results show that rare earth element have an effect...
Keywords/Search Tags:LB film, phthalocyanine, gas sensor, microsensor, FET, NO2, ultrathin film
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