A new doping approach of preparing VO<sub>2</sub> film was proposed to significantly tune the transition phase temperature. The heavy Ni-Cr-codoped VO<sub>2</sub> film ultra-thin layer was deposited on the pure VO<sub>2</sub> film by reactive pulsed magnetron sputtering on the Si substrate followed with annealing. The microstructure, optical and phase transition performance of VO<sub>2</sub> films were characterized via X-ray diffraction, UV/VIS/NIR spectrophotometer and thin film phase transition measurement system, respectively. The result indicates that the transition phase temperature of VO<sub>2</sub> film can be reduced from 53 ℃ to 30 ℃ by easily controlling different doping time.
Due to the interesting phase transition properties, Vanadium dioxide is a promising materials for smart windows. But phase transition temperature of 68° is high for this application. Doping is an useful method for transition temperature reducing in previous works. In this paper, different thickness VO<sub>2</sub> films were prepared by reactive pulsed magnetron sputtering, and a novel doping method was employed to reduce transition temperature. The results of XRD, Raman, transmittance spectra, and thermal hysteresis reveal that the transition temperature of un-doped samples is about 54~58°, and the increasing of phase transition amplitude and optical transmittance in visible decreasing with film thickness was observed. While for doped samples, all the transition temperatures reduced below 37°. For the thin thickness 12.5nm and 25nm, which phase transition performance deteriorated seriously. The thickness 25nm deposited for 1.5 h has the optimal performance of high optical transmittance and high IR adjustment ability.
In this paper we report a fiber optical sensor system based on surface plasmon resonance (SPR) with real-time response for biochemical interaction analysis. The fiber sensor is constructed from a multi-mode fiber with plastic cladding. To facilitate the measurement, a software program is developed which integrates the data acquisition and processing for real-time feedback. Polynomial fitting is implemented to smooth out the noise in the transmission ratio and a spectral resolution of 0.2 nm is achieved. Ethyl alcohol and water mixtures with different concentrations are measured to demonstrate the system's real-time capability. This work is essential for the development of a compact, real-time fiber SPR biosensor.
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.
A characteristic criterion of the growth of metallic films from discontinuous to continuous has been proposed. That is, when the electric conductivity σ of thin metallic film equals to 63.2% of the electric conductivity σ of the infinitely thick metallic film, the growth of metallic films come into continuous film. The corresponding equivalent thickness <i>d<sub>0</sub> </i>of the characteristic criterion can be thought of as the characteristic thickness of the growth of metal films from discontinuous to continuous. According this characteristic criterion, the characteristic thicknesses of Co films and Cu films have been given. The topography images of Co and Cu films have been observed using atomic force microscopy.