Preparation And Properties Of Indium Oxide Semiconducting Gas Sensors

The research of nano metal oxide gas sensor has been a hot spot in the research of nano materials science. At present, most of the detectors on the H2 S detection are stuck in the order of PPM magnitude. The detection of lower concentration H2 S is still a problem to be solved. In this paper, the main contents is to discuss the preparation methods, characterization methods, electrical test, optical test and gas sensitivity test of In2O3 nanomaterials, which is relating to the synthetic method, electrical properties, photosensitive properties and gas sensing properties of H2 S of the pure cubic crystal phase In2O3(Cubic-type In2O3), mixed crystal phase In2O3(Cubic-type In2O3 & Hexagonal-type In2O3) and pure hexagonal crystal phase In2O3(Hexagonal-type In2O3). The main work of this paper includes:1. The pure cubic-type In2O3 In2O3 was obtained by the simple solvothermal synthesis and a gas sensor was made by the obtained In2O3 nanoparticles. The In2O3 nanoparticles were characterized by XRD test, SEM test, TEM test, electrical test, UV test and gas sensitivity test. The results showed that the In2O3 nanoparticles were in a good dispersity, and the size was between 20 nm ~ 40 nm. The contact between the In2O3 particles was the ohmic contact, and the contact was very well. The In2O3 nanoparticles had an extremely sensitive to the UV, when the sensor based on the In2O3 nanoparticles was under the maximum UV irradiance, its response to UV was increased by 5 orders of magnitude. The optimum operating temperature of the sensor was 250 oC, and its lowest detection concentration to H2 S was 5 ppb. And finally, the gas sensing mechanism of the sensor was discussed in detail.2. The pure hexagonal-type In2O3 was obtained by the simple hydrothermal method and a gas sensor was made by the obtained In2O3 nanoparticles. The In2O3 nanoparticles were characterized by XRD test, SEM test, TEM test, electrical test, UV test and gas sensitivity test. The results showed that the In2O3 was in blocks of irregular shape, which surface was composed of compact and orderly In2O3 nanoparticles with a size of 5 nm ~ 10 nm. The contact between the In2O3 nanoparticles was ohmic contact. The sensor based on hexagonal-type In2O3 nanoparticles had a low sensitive to UV, when the sensor was under the maximum UV irradiance, its response to UV was increased by 13 times. At room temperature, the minimum detectable concentration of the sensor to H2 S was 10 ppb. At the same time, the sensor had a good stability and selectivity.3. The physical process of the synthesis of the mixed crystal phase In2O3 nanoparticles was obtained by the obtained precursor InOOH nanoparticles: the roasting temperature was 550 oC and the holding time was 120 min. By changing the ratio of In(NO3)3?4.5H2 O and the ethanol amine(C2H7NO) in the reactants, and through different roasting processes, three In2O3 nanoparticles with different crystalline phases were obtained finally. XRD, SEM characterization and gas sensitivity tests were carried out on these three materials. The results showed that the surface of the three samples was composed with a large number of nanoparticles, while the pure hexagonal-type In2O3 nanoparticles were in the best dispersity, and the nanoparticles were regular arrangement arranged and the size were basically in same. The electrical measurement results of the sensor based on the three samples showed that the sensor based on pure cubic-type In2O3 nanoparticles had the best electrical conductivity, the conductive properties of the sensor based on the mixed crystal phase and pure hexagonal-type In2O3 nanoparticles were basically in same. The gas sensing test results of three kinds of sensors were indicated that, to the same concentration of H2 S, the gas response of the sensor based on pure cubic-type In2O3 nanoparticles between the levels of the other two kinds of sensors, however, the response time and recovery time were the longest of all. The gas response of the sensor based on the mixed crystal phase In2O3 nanoparticles was the worst of all, while the response time and the recovery time were the shortest of all. The sensor based on the pure hexagonal-type In2O3 nanoparticles had the highest gas response, while the response time and recovery time were between the levels of the other two kinds of sensors. In the end, the sensor based on the pure hexagonal-type In2O3 nanoparticles was selected to do further research. TEM analysis was done on the pure hexagonal-type In2O3 nanoparticles, the results showed that there were a large number of holes in the particles, and the pore size were between 2 nm ~ 3 nm. Electrical test of the sensor indicated that the contact between the nanoparticles was ohmic contact. And the In2O3 nanoparticles had a good sensitive to the UV, when the sensor was under the maximum UV irradiance, its response to UV was increased by 5 orders of magnitude and the response time and recovery time were within 6.4 min and 5.2 min, respectively. The gas sensitivity test at room temperature showed that the sensor was very sensitive to H2 S and its lowest detection limit to H2 S was 1 ppb. At the same time, the sensor had a good stability and selectivity.