Silicon Nanowires Array For Gas-sensing Applications: Experimental And First-Principles Study

In this work,the adsorption and sensing mechanism of NO₂ on the noble metal-surface composite silicon nanowires?SiNWs?gas sensor is studied by combining experimental and theoretical methods.Theoretically,the adsorption characteristics towards NO₂ and sensitive mechanism of silver modified SiNW were investigated at the micro-atomic and molecular level based on the density functional theory?DFT?method.Firstly,the silicon nanowire model along[001]direction was established based on SiNWs array.And five different Ag-modified SiNW?Ag@SiNW?models were constructed and the modification energies(E_mod),density of states and electron transfer properties of the models were calculated.It was found that the Ag-Si₂&Si₂ is the best modification site.meanwhile,the electronic structure calculation results showed that the Ag modified system exhibits N-type doping characteristics.Furthermore,the adsorption model of NO₂ on Ag@SiNW was established,and the modification energy,density of States and electron transfer characteristics of the model were calculated.Compared with the adsorption of clean SiNWs,these results showed that NO₂ molecules form strong spontaneous adsorption on the surface of modified nanowires,and a shallow state is introduced due to the adsorption of NO₂ molecules.The theoretical results are in agreement with the experimental results.Finally,the adsorption of NO₂ on SiNW based on van der Waals junction is studied.The results showed that the van der Waals junction can improve gas sensing of SiNWs array theoretically.In the experimental aspect,a novel top-Cu₂O immobilization method was developed to fabricate aggregated interconnected?AI?SiNWs array with high structural stability.The deposition of Cu₂O clusters on the top of SiNWs array was achieved by multiple spin-coating with hydrofluoric acid?HF?/copper sulfate?CuSO₄?mixed solution.NO₂ sensing test results of AI SiNWs showed high sensitivity and fast response recovery characteristics to 30-2000 ppb of NO₂ at room temperature.Meanwhile,the sensor can be used to detect rare NO₂?the sensitivity of the sensor to30 ppb NO₂ is 2.25?.In addition,the sensitivity of the sensor to the same concentration of NO₂ is maintained above 90%in four weeks,indicating that it has good long-term stability.Through theoretical calculations and experimental investigations,surface recombination changes the surface state of SiNWs and further improves the sensitivity of SiNWs to NO₂ gas.