Design And Fabrication Of Nanobeam For Detecting Heavy Metal Ions In The Water Environment

With the development of microelectronics technology and nano-fabrication technology,nanobeams and nanowires are widely fabricated.Nanobeams are key components in a variety of applications of nano-mechanical systems,such as ultra-small mass detection,ultra-fast sensing,generation of very high frequency signals.Water pollution is a global problem especially heavy metal pollution.Heavy metal pollutant is one of the most prevalent and serious types of water pollutants.The technology and method on detection of heavy metals in water environment have been a research hotspot.However,there are some drawbacks exist in these ways,such as can’t be detected in field and on real-time,poor repeatability and stability.Trace detection of heavy metal ions in water environment based on the frequency shift of the vibration of silicon nanobeams is a new sensing method,a new technology,and a new proposal with ultra-high mass sensitivity and ultra-small sensing device.Fast trace detection can be achieved by this new proposal.A frequency shift will occur when the mass of a nanobeam changes.Fast trace detection of heavy metal ions will be realized by measuring the frequency shift of the nanobeam in this thesis.The creative point in this thesis is application of modifying Au electrode to the surface of silicon nanobeams.The uniform organosilica nanoparticles with small size are selected to modify the surface of Si-Au composite nanobeams,the adsorption and accumulation of heavy metal ions will be realized.The dependence of size on vibration of Si-Au composite nanobeams was simulated by molecular dynamics method and the fabrication process was manufactured in Suzhou Institute of Nano-Tech and Nano-Bionics.The achievements of this thesis will have a significant impact on detection of heavy metal ions.The main work is as follows:First of all,this thesis briefly describes the harm of heavy metal ions to human and the methods of detecting heavy metal ions,it also has an overview of nano-mechanical systems and lists many excellent characteristics of NEMS devices and their potential in some fields.The research process of sensors based on silicon nanobeam is studied.Secondly,this thesis introduces the principle of electrostatic excitation of NEMS resonator and vibration characteristics of resonant nanobeams,which can be prepared for the analysis of test results.The piezoresistive theory is described,which provides a theoretical basis for the design of structure and experiment.Thirdly,research on vibration of Si-Au composite nanobeams by molecular dynamics simulation is carried out and the dependence of size on vibration of Si-Au composite nanobeams is studied.Fourthly,this thesis analyzes and discusses the feasible fabrication process and provides the specific layout to manufacture the structure.Several typical NEMS fabrication processes are discussed and specific parameters of these processes in the experiment are prepared.It also shows SEM images of structure after fabrication.The vibration characteristics of the samples were studied by Laser Doppler Vibrometer.Finally,the organsilica nanoparticles modified the surface of Si-Au composite nanobeams are obtained,the morphology of the organsilica nanoparticles is characterized by scanning electron microscope(SEM),and the detection of heavy metal ion Pb2+ is realized.