High Quality VO₂ Thin Films Grown With Their Characteristics By MBE

Scientific studies have shown that vanadium has variety of valence states,which is easy to form variety of compounds,and these vanadium-oxygen compounds all have relatively unique phase transition properties.Among them,vanadium dioxide（VO₂）has become the focus of people’s attention and research.The critical phase transition temperature of VO₂ is 68 oC,which has unique phase change property with the change of lattice structure with temperature.At low temperatures,VO₂ is monoclinic semiconductor or insulator phase with high resistivity;at high temperatures,VO₂ is metal phase with low resistivity tetragonal rutile structure.Therefore,due to its unique characteristics,its other photoelectric properties have also been changed,which makes VO₂ had wide range of application prospects in smart materials,smart regulation and intelligent energy-saving fields.In order to explore the application and stability of VO₂ thin film in these areas,high-quality VO₂ film samples were prepared by MBE,and its application performance in THz modulators and smart windows,as well as its stability were studied.What’s more,the paper is also to explore the microscopic mechanism of the phase transition of VO₂ and the change of their photoelectric properties,which is aim to provide theoretical guidance for the wide application of VO₂ as an energy and functional material.The content of this paper:（1）The modulation characteristics of THz waves for four different thicknesses of VO₂ thin film samples grown on sapphire substrate by MBE were studied.X-ray diffraction（XRD）,atomic force microscopy（AFM）and other basic characterizations were used to analyze the crystalline quality and basic structure of VO₂ films grown on sapphire substrates.In addition,THz time-domain spectroscopy tests were also performed.The results show that the thickness of VO₂ film has modulation effect on THz waves which is an ideal material for switching devices and THz modulators.（2）The thermochromic smart window application of three different thickness VO₂ thin film samples grown on the silica glass substrate by MBE was studied.Using basic characterization methods,the physical and chemical properties of the sample were tested and analyzed.The results show that the VO₂ samples grown on the quartz glass substrate have better variable temperature transmission characteristics and the transmittance exceeds 80%.（3）The phase transition stability of three different thicknesses of VO₂ thin films grown on sapphire substrate by MBE was studied,including the life-time phase transition stability and the effect of the temperature change rate on the phase transition.At the same time,X-ray photoelectron spectroscopy（XPS）analysis results showed that under normal environmental conditions,the phase transition stability of VO₂ was acceptable,but due to factors such as the oxidation of the surface of the sample before and after the storage time,the metal of the VO₂ film was affected.Through the experiments and characterization analysis,we know that the thickness of VO₂ film has modulation effect on THz wave which is an ideal material for switching devices and THz modulators;the vanadium dioxide thin film grown on quartz substrate has good transmittance.It is an ideal material for the thermochromic smart window layer.At the same time,VO₂ film has good phase transition stability which provides protection for practical device applications.