Study On The Fabrication And Doping Modiifcation For Uniaxially Aligned In₂O₃Nanofibers In Gas Sensor

Along with the improving standard of living, the requirements for liveenvironment and production process control are getting higher and higher. Gassensors, a kind of devices which are applied to detect gas components in air, emergeas the times require. Metal oxide semiconductor gas sensors, as one kind of gassensors which possess good mechanical, high stability, long service life and low costproperties, are widely studied and used. In this paper, a kind of gas sensors with goodgas sensing properties is reported.In this paper, well-aligned architectures, noble metal Au and metal oxide CdOdoping modification are applied to improve the gas sensing performances of In₂O₃materials.The fabrication and gas sensing properties of uniaxially aligned In₂O₃nanofiberswere studied in the first part of the experiment. In（NO₃）₃·4（1/2）H₂O was used asprecursor to fabricate uniaxially aligned In₂O₃nanofibers with amagnetic-field-assisted electrospinning method. The X-ray diffraction （XRD） resultshowed that the fibers were made up of cubic In₂O₃, the scanning electron microscopy（SEM） results showed that the fibers were uniaxially aligned and the diameters wereuniform and around100nm. Indirect-heating sensors using uniaxially aligned In₂O₃nanofibers as sensitive materials were fabricated on a Al2O3substrate with Auelectrode on one side and Ru₂O₃heating layer on the other side and gas sensingproperties were investigated. It is found that when the operating temperature is245°C,the response of the sensors reach3.2to50ppm of Cl₂, and the response and recoveryproperties are good; when the operating temperature is275°C, the response of thesensors reach4.3to50ppm of NO₂, and the response and recovery properties aregood; and when operating temperature is120°C, the response of the sensors reach17to500ppm of C2H5OH, and the response and recovery properties are good.Au-loaded In₂O₃nanofibers, with different Au concentrations changing from0.1wt%to0.4wt%, were successfully prepared in the second part of the paper usingIn（NO3）3·4H2O and HAuCl₄as precursor with a typical electrospinning method. The XRD results showed that the fibers were made up of cubic In₂O₃, while the Audiffraction peaks were not observed because of the low concentration. The SEMresults showed that the fibers were uniform and the diameters were around100nm.Direct-heating sensors based on Au-loaded In₂O₃nanofibers with different Auconcentrations were fabricated on a silicon substrate with micro hot-plate and signalelectrodes. The ethanol sensing properties of the sensors were investigated. It is foundthat the sensors based on the0.2wt%Au-loaded In₂O₃nanofibers possessed betterethanol sensing properties than those based on other Au concentration （0.1,0.3,0.4wt%）. When the operating temperature is140°C, the response of the sensors to500ppm of ethanol is13.8, the response and recovery time is12s and24s, respectively.Meanwhile, the heating current is35mA and the resistance of the heaters under thisheating current is105Ω. The calculated power consumption of the sensors reachedmaximum response is222.5mW. Compared with the sensors reported previously, thispower consumption value is relative low and with this property, the micro-structuresensors can be used as on-line ethanol gas sensors.In the third part of the paper, uniaxially aligned0.2wt%Au-loaded In₂O₃nanofibers were fabricated, the optic microscopy photos showed that the fibersuniaxially aligned. Direct-heating sensors based on uniaxially aligned0.2wt%Au-loaded In₂O₃nanofibers were fabricated, and the ethanol sensing properties of thesensors were investigated. It is found that the unixaxially aligned fibers showed betterresponse and recovery properties than the randomly deposite fibers.In the last part of the paper, the CdO mixed In₂O₃materials with a molar ratio of1:2were prepared by conventional electrospinning method, followed by calcination atdifferent temperature. The effect of calcination temperatures on the gas sensingproperties of the mixed materials was investigated. The XRD results showed that thefibers were made up of In₂O₃and CdInO₄after calcining at600°C. The samplesobtained by calcination at600°C showed better gas sensing properties to ethanol,compared with those calcined at other temperatures such as500°C,700°C and800°C. The detailed mechanism of this phenomenon will carry out in the furtherwork.