Study On The Sensing Properties Of Low-dimensional Nanostructure Metal-oxide Semiconductors

Sensing materials have been evolved from bulk materials to large-sized particle materials, to small-sized particle materials, and to low-dimensional nanomaterials. In recent years, low-dimensional nanomaterials have attracted much focus owing to their anti-aggregation, high surface area, and oriented electron conduction.This paper aims at describing the humidity and gas sensing properties of some low-dimensional nanostructure metal-oxide semiconductors (MOS) (ZnO, TiO2, and SnO2).Flower-like ZnO nanorods are synthesized via a hydrothermal method. The impedance of the corresponding sensor decreases by about 5 orders of magnitude with increasing relative humidity (RH) from 11% to 95%. The response time is about 5 s (from 25% RH to 95% RH), and the recovery time is about 10 s. The sensing mechanism of flower-like ZnO nanorods is discussed based on complex impedance plots.KCl-doped ZnO nanofibers are synthesized via an electrospinning method. The humidity sensing properties of these fibers can be concisely controlled by adjusting the compositions in their precursors. For pure ZnO nanofibers, the impedance changes only about 1 order of magnitude with poor linearity on a semilogarithmic scale. While the 5.7 wt% KCl-doped ZnO nanofibers show improved humidity sensing properties with their impedance varying more than 5 orders of magnitude and better linearity. Especially, the response time and recovery time of KCl-doped ZnO nanofibers is only about 2 and 1 s, respectively (from 25% RH to 95% RH).KCl-doped Cu-Zn/CuO-ZnO nanoparticles in mass production are synthesized via a wire electrical explosion method. The impedance of the corresponding humidiy sensor varies about 4 orders of magnitude in the range of 11% to 95% RH. The response and recovery times are about 40 and 50 s, respectively (from 25% RH to 95% RH).KCl-doped TiO2 nanofibers with different crystallographic structures (anatase, rutile, and mixed anatase and rutile structures) are synthesized via an electrospinning method, and their humidity sensing properties are investigated. The KCl-doped TiO2 nanofibers with mixed structures show the highest sensing performance among all the fibers. The impedance of this sample linearly decreases by more than 4 orders of magnitude with increasing RH from 11% to 95% on a semilogarithmic scale. The response and recovery times are about 3 and 4 s, respectively (from 25% RH to 95% RH).Dumbbell-like ZnO microcrystals are synthesized via a hydrothermal method. The sensor fabricated from these microcrystals exhibits high CH3COCH3 sensing properties at 300°C. The response is about 4 to 1 ppm CH3COCH3, the response time is about 1.5 s, and the recovery time is about 3 s. Especially, the sensor presents successful discrimination between CH3COCH3, and C2H5OH.SnO2 nanofibers with and without template agent in the precursor are synthesized via an electrospinning method. Gas sensing properties of these two samples are investigated by exposing the corresponding sensors to NH3, C2H5OH, CH3COCH3, and C6H5CH3, respectively. Comparing with nanofibers without template agent, the SnO2 nanofibers with template agent hold enhanced response value and higher saturated-detection-concentration. The response is 28 for the nanofibers without template agent to 500 ppm NH3 at 280°C, and is 59 for the nanofibers with template agent. The corresponding saturated-detection-concentration is 2000 and 5000 ppm, respectively. Similar improvements are also observed in the cases of C2H5OH, CH3COCH3 and C6H5CH3.Sm2O3-doped SnO2 are are synthesized via a sol-gel method. The sensor based on 6 wt% Sm2O3-doped SnO2 displays high C2H2 response at 180°C. The response is about 3 to 10 ppm C2H2, the response and recovery times are 3 and 17 s, respectively.In/Pd-doped SnO2 is synthesized via a sol-gel method and coated on a silicon substrate with Pt electrodes to fabricate a micro-structure sensor. The heater electrodes and signal electrodes of the sensor are designed on the same plane with the same cathode. The sensor response is about 3 to 1 ppm CO, the response and recovery times are 15 and 20 s, respectively.A temperature measurement based on radicalization power for micro-hotplate is designed and fabricated. By means of comparing the relation between the radialization power and the temperature, the temperature of a micro surface area can be accurately discerned. The experimental result based on this method is quite similar to that of simulation by the finite element analysis (FEA) software of Ansys in theory.