Preparation And Properties Of Vanadium Dioxide Composite Film

Vanadium dioxide is a transition metal oxide with thermal phase transition properties.It has four types,namely A,B,M,and R.In recent years,vanadium dioxide in monoclinic phase?M?and rutile phase?R?has attracted much attention due to its property of thermally reversible phase transition between its insulating phase and metallic phase,and compare to other transition materials the transition temperature of vanadium dioxide has minimal difference from room temperature.When the temperature attaches 68??341 K?,the phase transition will occer.There is no change in composition of vanadium dioxide during the phase transition process,that is,no chemical reaction occurs during the phase change,only the structure change occers.And at low temperature vanadium dioxide is in the monoclinic insulating state?M type?,while it becomes a tetragonal metallic phase?R type?at high temperature.In this thermally-induced phase transition,not only does the resistance change by several orders of magnitude,but also the abrupt change occurs in optical properties,which manifests itself from a low-temperature,high-transmission state to a more opaque state at high temperature,which indicates that VO₂ can modulate the light response automatically by adjusting the temperature.Vanadium dioxide has become a hot research topic in the field of functional materials such as smart windows and optical switches because of its excellent thermal-induced phase transition properties.Terahertz refers to electromagnetic waves covering the frequency band of 0.1THz to 10 THz.The wavelength range is about 0.03 mm to 3 mm.It has important applications in radar detection,wireless communication,and substance detection.Since the requirements for the use of terahertz waves are different in various fields,in order to further promote the application of terahertz in real life,it is necessary to provide a modulation device which has a good efficiency on terahertz waves modulation.In this context,VO₂ film and metal grating structure were combined to prepare a composite film with good modulation effect on terahertz wave.In this paper,the method and process of preparing vanadium dioxide thin film by polymer-assisted deposition method?PAD?are firstly studied,and vanadium dioxide thin film with good MIT characteristics is obtained.X-ray diffraction analyzer?XRD?,scanning electron microscope?SEM?,atomic force microscopy?AFM?,Raman spectroscopy and four-probe resistance test were used to test the micro-structures and electrical properties.The test results display that the films grown by the PAD method have good crystallization and excellent electrical properties.Next,the process steps of composite film were discussed,and the effects of photolithography process parameters such as exposure time,development time,and spinning speed on the prepared grating structure were mainly studied.Through optimization of process parameters,metal grating with complete and uniform lines was prepared.The effect of the metal grating structure on the crystal orient,surface and section morphology,and electrical MIT properties of the vanadium dioxide was analyzed.The results show that the crystal orientation of the composite film is changed after adding grating structure,and the grating period is increased,and the height of the surface undulation is also increased.And the electrical properties are reduced.This shows the addition of the grating has an impact on the growth of the film.Finally,the terahertz performance of the prepared vanadium dioxide and the composite film combined with the grating were studied,and the experimental results were further verified by simulation.The terahertz transmission properties of vanadium dioxide films with different temperature and different resistance phase transition characteristics were tested.The experimental test analysis shows that the transmission response amplitude of the film to terahertz can be adjusted by controlling the temperature,and the quality of the VO₂ film,especially the MIT characteristics,is of great significance for terahertz modulation.In addition,the effect of different grating period on the terahertz modulation effect was studied.Transmission terahertz time-domain spectrum analysis of vanadium dioxide composite thin film samples with metal gratings with the same duty cycle and different period were performed.The test results display that when the grating period increases,the terahertz modulation depth becomes higher.Simulation results show that the modulation depth is related to fluctuation height of film which can be modulated by grating period.Compared with the modulation performance of pure vanadium dioxide,although the MIT characteristic of the composite film is reduced,it can still maintain a high THz transmittance,indicating that this composite film can achieve effective regulation of terahertz,and it is useful for the promotion of terahertz waves in practice.