Research Of The High Performance Gas Sensors With Modified Silicon Nanowire Array

Surface or structure modification can be considered as a very effective way to improve the properties of a gas sensor.In the past,the surface modification and structure modification were two independent modification systems,resulting a limitations on the improvement of gas sensor performance.What is more,the modification process was complicated.In this work,we develop a novel and cost-effective process to prepare Ag modified silicon nanowires?SiNWs?sensor,and further suggest a resistance effect model to clarify the enhanced sensing mechanism of Ag-modified SiNWs.In this process,the SiNWs were formed via metal-assisted chemical etching?MACE?with aim to compere the sensitive properties with the sample fabricated by our process;anisotropic etching of tetramethylammonium hydroxide?TMAH?is a crucial step in metal and structure modification of our process.The TMAH post-etching introduce the pits on the surface of silicon nanowires formatting the rough structure?RNW?,and taper nanowires forming the needle-like structure to achieve the structural modification.The modification of the silver nanocrystals is based on the partial removal of the silver branches generated in the MACE process with aim to the complete pre-modification of the silicon nanowires by the silver.After the following TMAH post-etching,the nanowire will introduce structure modification and make the silver particles rearrange to form a stable and uniform modification on the surface of the silicon nanowires at the same time.Many tiny Ag nanodots with size of 2-6 nm are observed to be inlaid on the rough surface of RNW,as revealed by the SEM,TEM and XPS analysis.The increased specific surface area by the TMAH post-etching process is obtained from a BET method.The gas-sensing properties of smooth,rough and silver-modified rough silicon nanowires were tested at room temperature.The comparison shows that the sensing performance of Ag-modified rough silicon nanowires is significantly improved compared with unmodified silicon nanowires.The as-prepared Ag NPs@RNWs sensor demonstrates high sensitive response to ultra-rarefied NO₂ gas?10ppb?and NH₃ gas?330ppb?with very short response time of 12s and<2s,respectively at room temperature,indicating the considerable effect of the Ag NPs modification process developed here.Comparative investigations for NO₂-and NH₃-sensing properties also indicate that the RNWs modified by discrete Ag NPs?Ag@RNWs?display a³-fold enhancement in gas response at room temperature.The study demonstrates the considerable effect and potential of the Ag modification process developed in this work.A resistance effect model was further suggested to clarify the underlying mechanism of the enhanced response characteristic of the Ag NPs and structure modification.