Research On Micro-nano Electromechanical Resonance Technology For Detection Of Heavy Metal Ions In Water Environment

Heavy metals are widely used in modern industry,but the heavy metal pollution has become increasingly serious.It has endangered the environment and human health,and has become a global problem.An efficient and fast method for detecting heavy metal ions in water is needed,which is conducive to build a sustainable,effective and real-time monitoring and treatment system for heavy metal pollution.With the rapid development of micro/nano-electromechanical technology,resonant sensors have been found in trace detection of different substances.Due to small size,high sensitivity,and low cost,they can be used to detect heavy metal ions in water environments.Cantilevers and doubly-clamped beams in different sizes are designed for detection of heavy metal ions.The beams are actuated by electrostatic force and the resonant frequency of beam vibrations can be measured by utilizing the piezoresistive effect.The mesoporous silicon nano-particles functionalized with thiophene groups are prepared as the modified material on the surface of beams for the adsorption of heavy metal ions,to realize the detection of some of heavy metal ions,like Pb²⁺,Hg²⁺,and Cd²⁺.The main work of the paper is as follows:First,a new coupled resonant sensor consisting of doubly-clamped beams is designed based on SOI process.The resonator is used to detect the mass of blocks on each beam by measuring the two resonant frequencies.The experimental results show that comparing the symmetric resonant mode,the asymmetric resonant mode of coupled beams is more suitable for the micro mass detection.Secondly,the COMSOL software is used to simulate the resonant frequency and the piezoresisitive effect of the designed micro-nano beam resonator.Based on the simulation results,the mass sensitivity of the beam is deduced and the design is verified.The device structures are improved and optimized further.The new structure of the Cr-Au layer is designed to protect the aluminum electrode.Several experiments are carried out on the process of the piezoresistive injection zone to determine the relevant process parameters.The process flow is adjusted to improve the yield of the device.The characterization of the fabricated beams is performed and the problems about structural design and process arrangements are discussed in detail.Finally,the mesoporous silicon nanoparticles functionalized with mercapto groups are prepared by the template method as the modification material of the resonator surface.The mesoporous silicon nanomaterials are characterized by SEM,and the heavy metal adsorption experiments are carried out.