Vanadium dioxide is one of the reversible phase transition materials, which can be induced by temperature, electric field, laser, stress, etc. This characteristic makes thin films have great potential applications in fields of various optoelectronic devices. For electro-optical switch applications, a high extinction ratio and low threshold voltage are required, which are closely related to the VO2 film thickness. In this paper, VO2 thin films with different thicknesses were deposited on ITO substrates by pulsed magnetron sputtering. Microstructure, optical and electrical properties, and phase transition performance of the samples are investigated. The research results have a high reference value for the design of high-performance VO2-based electro-optic switches.
VO2 thin films were fabricated by reactive DC magnetron sputtering on different buffer layers of MgF2, Al2O3 and TiO2, respectively. The crystallinity and orientation relationship, thickness of VO2 thin films, atoms vibrational modes, optical and electrical property, surface morphology of films were characterized by X-ray diffraction, Raman scattering microscopy, step profiler, spectrophotometer, four-probe technique, and scanning electron microscopy, respectively. XRD results investigated that the films have preferential crystalline planes VO2 (011). The crystallinity of VO2 films grown on TiO2 buffer layers are superior to VO2 directly deposited on soda-lime glass. The Raman bands of the VO2 films correspond to an Ag symmetry mode of VO2 (M). The sample prepared on 100nm TiO2 buffer layer appears nanorods structure, and exhibits remarkable solar energy modulation ability as high as 5.82% in full spectrum and 23% in near infrared spectrum. Cross-sectional SEM image of the thin films samples indicate that MgF2 buffer layer has clear interface with VO2 layer. But there are serious interdiffusion phenomenons between Al2O3, TiO2 buffer layer with VO2 layer.
Vanadium oxide thin films were prepared by DC reactive sputtering method, and the samples were annealed in Ar atmosphere under different temperature for 2 hours. The microstructure, optical and electrical properties of the as-grown and treated samples were characterized by XRD, spectrophotometer, and four-probe technique, respectively. XRD results investigated that the main content of the annealed sample are VO2 and V2O5. With annealing temperature increasing, the intensity of the VO2 phase diffraction peak strengthened. The electrical properties reveal that the annealed samples exhibit semiconductor-to-metal transition characteristic at about 40°C. Comparison of transmission spectra of the samples at room temperature and 100°C, a drastic drop in IR region is found.
Micro-defect is one of key limiting factors in the improvement of the laser-induced damage threshold (LIDT) of thin
films. In the present paper, thin films were prepared using the electron-beam evaporation technique with different
coating materials and pre-melting processes. The relationships of thin film LIDT with impurity element content and with
pre-melting processes were investigated. The experiment results indicate that a number of impurity elements play an
important role in the LIDT of the samples. An efficient pre-melting process is necessary to maintain deposition stability,
which could also reduce micro-defect density in thin films.
Laser-induced damage of optical thin films is one of the main obstacles, which prevents laser technology from being developed toward high power. Many experimental results indicated that microdefect and absorption of films are the two major factors that influence laser induced damage threshold (LIDT). To reduce microdefect density and absorption, and improve LIDT of thin films, researchers have developed not only novel film deposition techniques, but also novel film post-treatment techniques. Though film deposition techniques have been highly developed, microdefect still remains to be the main limited factor of LIDT. Because of this, posttreatment techniques as a novel way to reduce defect density and improve LIDT has (been) attracted much attentions. One of the most frequently used posttreatment methods is laser conditioning and another is ion posttreatment. By comparing the treatment mechanism of two posttreatment techniques, it is easy to find their similarities and differences. Though laser conditioning is a classical posttreatment technique, its shortages such as low efficiency, rigorous requirement of equipment stability, and uncertain treatment results are inevitable. As a novel technique, ion posttreatment has great potential to improve LIDT of thin films. This technique not only has high treatment efficiency, but also has convenience and easily adjusted parameters. So it should be a promising posttreatment technique in improving LIDT of optical thin films.
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