Silicon Based Metal Oxide Heterostructure Gas Sensor

In recent years,with the improvement of living standards and the awareness of environmental protection,people are increasingly demanding their own health and living environment.It is urgent to monitor various toxic,harmful,flammable and explosive gases in various fields such as environmental protection,medical health,industrial production,aerospace military engineering.Based on the above facts,the related research of new high-performance gas sensor is of great significance and has broad application prospects.In this paper,nano-semiconductor metal oxides WO₃ and V₂O₅ are grown on porous silicon(PSi)surface by different methods,and the noble metal palladium is loaded to prepare a high performance Pd loaded PSi/WO₃ and PSi/V₂O₅ nanocomposite gas sensor for NH₃,NO₂.The effects of different preparation methods and loading conditions on the performance of nanocomposite gas sensor and related regulation mechanism were studied.The specific research contents are as follows:The PSi/WO₃ nanowire was prepared by the method of thermal evaporation W powder.The WO₃ nanowire with a small amount of oxygen defects was monoclinic crystal structure with good crystallinity,diameter of 10-40 nm and length of 1-3?m,due to the composite with PSi,the optimal operating temperature of WO₃ nanowires is reduced to room temperature.The palladium nanoparticles were loaded on the surface of WO₃ nanowires by solution method.The results show that the reduction time affects the loading density and siez of palladium particles.The gas-sensitive properties of the Pd laoded PSi/WO₃ nanowire have been significantly improved:the detection limit of NH₃ is as low as 1 ppm,and the sensitivity to 100 ppm NH₃ is up to5.The response is fast and the response time is 3-10 s.The PSi/WO₃ nanowire(rod)was obtained by thermal oxidating the W film which deposited on the surface of the PSi,and the Pd loading was carried out at different concentrations.The effects of W film thickness and thermal oxidation temperature on the PSi/WO₃ nanowire(rod)were investigated.The results show that high-density orthorhombic WO₃ nanowires(rods)with diameter of 40-60 nm and length of 1-4?m are grown on the surface and pores of PSi by thermal oxidating 100 nm W film at700°C.The PSi/WO₃ nanowires(rods)were modified with different concentrations of Pd particles.When the Pd loading was in the range of 20-60 mg,the sensitivity to NO₂ increased with the increase of Pd concentration.The sensitivity to 2 ppm NO₂was improved 5.2,the relative increase is 73%,the minimum detection is up to 250ppb,the response/recovery time is shortened,and the selectivity to NO₂ is good.The PSi/V₂O₅ nanoplate composite was prepared by magnetron sputtering deposition of the V film and thermal oxidation.The growth mechanism of V₂O₅ nanoplates was systematically analyzed by studying the key parameters such as V film thickness,thermal oxidation temperature and thermal oxidation time.The Pd-loaded composite has higher sensitivity to NO₂ due to the catalytic overflow effect of Pd on the PSi/V₂O₅ nanoplate.The sensitivity of the Pd-loaded composite is 5.12 times that of the PSi/V₂O₅ nanoplate,the response is rapid,and the recovery time is shortened.The PSi/V₂O₅ and Pd particles jointly affect the gas sensing performance of the sensor.