| Ultraviolet(UV)sensor is a high-precision detector for electromagnetic wave with a wavelength of 10 nm-400 nm.This sensor has a wide range of applications,such as air-to-air safety communications,environmental monitoring,water sterilization,flame detection and monitoring for missile tail flame.Therefore,it is important to prepare rapidly miniaturized UV sensors and improve the sensitivity and response speed of UV sensors.In various manipulation systems of nanoscale objects,the conductive-island nanogap electrode is a system in which conductive structures are added between planar electrodes and nanogaps exist between the electrodes and the conductive structure or between the structures.The parallel rapid assembly of nanomaterials can be acted in a conductive-island nanogap electrode system.The integration level of the devices can be improved due to the working gap reduction into nanoscale(nanogap).Moreover,the response speed becomes faster because nanogap shortens the carrier transport time.In addition,with the decrease of gap sizes,the probability of electron captured by semiconductor can also reduce,and the probability of electron captured by electrode increases,which improves the responsiveness of nanogap based devices.A UV sensor based on the conductive-island nanogap electrode system was prepared by dielectrophoresis in the thesis.The major work covered in this thesis includes:Firstly,methods for fabricating planar nanogap electrode were investigated.The technological process of preparing traditional nanogap electrode and the advantages and disadvantages of the methods were analyzed.The fabrication of nanogap by photolithography and swelling of organic material were studied.Swelling time was the most effective way to control the width of nanogap,providing a technological basis for the preparation of the conductive-island nanogap electrode used in subsequent dielectrophoretic assembly experiments.Secondly,dielectrophoretic assembly model of nanoparticles in the range of high frequency in the conductive-island nanogap electrode system was established on the theory of non-uniform alternating current(AC)electric field electrohydrodynamics,and explored the frequency-dependent characteristics and rules of nanoparticle wire forming.By using numerical simulation method,the dielectrophoresis force,the electrothermal fluid flow and the combined electrodynamic behavior of nanoparticles were analyzed in the conductive-island nanogap electrode system.In the process of dielectrophoretic assembly,the nanoparticles are affected by the positive dielectrophoresis force which is largest at the edges of the nanogap.With the increasing frequency,the flow direction of AC electrothermal flow in the calculation domain will reverse,and the vortex in the nanogap will disappear gradually.There are two assembly modes of nanoparticles found in the dielectrophoresis assembly process: bulk assembly in the nanogap,and surface assembly on the surface of electrode and conductive island.Moreover,assembly mode can be affected by frequency,which lead to the different distribution and morphology of nanoparticle wires formed by the dielectrophoresis assembly.The related research provides theoretical support and practical basis for the controllable assembly of nanoparticles in the conductive-island nanogap electrode system.Thirdly,based on the theory of double-layer polarization induced by AC non-uniform electric field,the influence of electroosmotic flow on the dielectrophoretic assembly behavior of nanoparticles at low frequency was explored.It was found that AC electroosmotic flow can play a major role in the far-field region and transport nanoparticles into the assembly region,while the dielectrophoresis force which causes the dielectrophoretic assembly of nanoparticles was a dominant factor in the near-field region.The results of the experiments at low frequency show that the nanoparticles can be dielectrophoretic assembled into a small number of nanoparticles wires between the conductive island and the electrode,and incomplete channel structures can be formed at the edge of the nanogap.This work lays a research foundation for the subsequent improvement of sensor performance.Finally,the UV sensor based on the conductive-island nanogap system was prepared,and the effect of the dielectrophoretic assembly frequency on the performance of the UV sensor was explored.The results show that the sensor has nonlinear current-voltage characteristics,and the amplitude of photocurrent is significantly higher than that of dark current.At the same time,the UV sensor prepared at different frequencies had higher response speed.The goal of preparing high-performance UV sensor based on the conductive island nanogap electrode was achieved.In summary,aiming at the conductive island nanogap electrode system,a wide-band dielectrophoretic assembly model of nanoparticles was established and the dielectrophoretic assembly experiments were carried out,and clarified the influence of AC electrokinetics effect on nanoparticle assembly and the rules of nanoparticles wires forming.Based on the above research,the UV sensor based on the conductive-island nanogap electrode system was prepared.This kind of sensor provides a technical possibility for the high-precision detection of UV,and points out the direction for the manufacture of high-performance UV sensor. |
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