Fabrication and Infrared Optical Properties of Nano Vanadium Dioxide Thin Films

Vanadium dioxide thin films were fabricated by ion beam sputtering on Si3N4/SiO2/Si after a post reductive annealing process in a nitrogen atmosphere. X-ray Diffraction (XRD), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS) were employed to analyze the effects of post annealing temperature on crystallinity, morphology, and composition of the vanadium oxide thin films. Transmission properties of vanadium dioxide thin films were measured by Fourier transform-infrared (FT-IR) spectroscopy. The results showed that the as-deposited vanadium oxide thin films were composed of non-crystalline V2O5 and a tetragonal rutile VO2. After annealing at 400 degrees C for 2 h, the mixed phase vanadium oxide (VOx) thin film changed its composition and structure to VO2 and had a (011) oriented monoclinic rutile structure. When increasing the temperature to 450 degrees C, nano VO2 thin films with smaller grains were obtained. FT-IR results showed that the transmission contrast factor of the nano VO2 thin film was more than 0.99 and the transmission of smaller grain nano VO2 thin film was near zero at its switched state. Nano VO2 thin film with smaller grains is an ideal material for application in optical switching devices.

Mode Analysis for Equilateral-Triangle-Resonator Microlasers with Metal Confinement Layers

Mode characteristics are analyzed for electrically injected equilateral-triangle-resonator (ETR) semiconductor microlasers, which are laterally confined by insulating barrier SiO2 and electrode metals Ti-Au. For the ETR without metal layers, the totally confined mode field patterns are derived based on the reflection phase shifts, and the Q-factors are calculated from the far-field emission of the analytical near field distribution, which are agreement very well with the numerical results of the finite-difference time-domain (FDTD) simulation. The polarization dependence reflections for light rays incident on semiconductor-SiO2 -Ti-Au multi-layer structures are accounted in considering the confinement of TE and TM modes in the ETR with the metal layers. The reflectivity will greatly reduce with a Ti layer between SiO2 and Au for light rays with incident angle less than 30 especially for the TE mode, even the thickness of the Ti layer is only 10 nm. If the ETR is laterally confined by SiO2-Au layers without the Ti layer, the Fabry-Perot type modes with an incident angle of zero on one side of the ETR can also have high Q-factor. The FDTD simulation for the ETR confined by metal layers verifies the above analysis based on multi-layer reflections. The output spectra with mode intervals of whispering-gallery modes and Fabry-Perot type modes are observed from different ETR lasers with side length of 10 m, respectively.

Magnetic properties and rectifying behaviour of silicon doped with gadolinium

The magnetic/nonmagnetic p-n junction was prepared by implanting gadolinium into the n-type silicon with low-energy dual-ion-beam epitaxy technology. The magnetic layer GdxSi1-x shows excellent magnetic properties at room temperature. High magnetic moment 10mu(B) per Gd atom is observed, which is interpreted by RKKY mechanism. Magnetic/nonmagnetic p-n junctions show rectifying behaviour, but no magnetoresistance is observed.

Experiment on Qinghai-Tibet railroad subgrade temperature monitoring based on FBG sensors

Qinghai-Tibet Railway is the longest and highest plateau railway in the world. A long term monitoring system of the stability of the subgrade in the permafrost regions should be put forward immediately to prevent damage to the railway. As it's very difficult to set up the long-distance automatic monitoring system which contains a lot of measure points along the 550 kilometers railway in the permafrost area, we present a subgrade temperature monitor system based on fiber Bragg grating (FBG). In this paper the principles of the FBG was presented, and the feasibility of the FBG sensors in the permafrost area of Qinghai-Tibet plateau was analysized. We embedded fifteen FBG temperature sensors and thermal resistance temperature sensors. A contrast experiment is made while the two kinds of sensors are arranged in the same position. The result of the experiment shows that the accuracy of the FBG temperature sensors is less than 0.1 degrees C. and the FBG sensors can do well in the measurement of pattern which the temperature varies with the depth of the permafrost soil. The result also shows the stability of the FBG sensors in the bad environmental condition of Qinghai-Tibet plateau, which proves the feasibility of the application of FBG sensors and our monitoring system on the Qinghai-Tibet railway.

纳米二氧化钒薄膜的制备及红外光学性能

采用双离子束溅射方法在Si_3N_4/SiO_2/Si基底表面沉积氧化钒薄膜,在氮气气氛下热处理获得二氧化钒薄膜.利用x射线衍射(XRD)、扫描电子显微镜(SEM)和X射线光电子能谱(XPS)研究了热处理温度对氧化钒薄膜晶体结构、表面形貌和组分的影响,利用傅里叶变换红外光谱(FT-IR)对二氧化钒薄膜的红外透射性能进行了测试分析.结果表明,所制备的氧化钒薄膜以非晶态V_2O_5;和四方金红石结构VO_2为主,经400℃、2 h热处理后获得了(011)择优取向的单斜金红石结构纳米VO_2薄膜,提高热处理温度至450℃,纳米结构VO_2薄膜的晶粒尺寸减小.FT-IR结果显示,纳米VO_2薄膜透射率对比因子超过0.99,高温关闭状态下透射率接近0.小晶粒尺寸纳米VO_2:薄膜更适合在热光开关器件领域应用.

基于仿生模式识别的DOA估计方法

该文就仿生模式识别(拓扑模式识别)在非感性抽象对象的信息处理方面的应用作了一些探索,提出了一种基于仿生模式识别的DOA估计方法.这种方法的建模过程是用在实际环境下采集的训练样本构造人工神经网络模型,对环境的适应能力较强,且这种方法的计算量较小,可以实现系统实时处理.实验结果表明:在信噪比为20 dB和0 dB时,该方法的正确估计率可达100%;在信噪比降为-20 dB时,该方法仍有83%的可识别率.

Si被注入Gd后的磁性及其整流特性的研究

采用离子束技术,在n型硅基片中注入稀土元素钆,制备了磁性-非磁性p-n结.磁性层Gd_xSi_(1-x)表现出优良的磁学性能,高居里温度,高原子磁矩(利用RKKY模型可以得到解释),低矫顽力,并保持着半导体的属性,磁性-非磁性p-n结具有整流特性,但没有观察到明显的磁电阻效应.