【作者】 刘玲玲；

【导师】 韩民；

【作者基本信息】 南京大学 ， 材料物理与化学， 2011， 硕士

【摘要】 二氧化钒(VO2)在340K附近会发生一阶的金属-半导体相变,从低温单斜晶相转变成高温金红石四方晶相,并同时伴随着电阻率、近红外区域透射率和反射率的突变。热致相变产生的应变对体材料会造成很大的危害,而VO2薄膜和纳米粒子点阵则没有这个问题。本文以金属钒V为先驱物,通过等离子体气相聚集团簇束流沉积的方法制备含有VO2成分的钒氧化物纳米粒子组装薄膜。室温下半导体相的VO2纳米颗粒,由于量子限制效应导致光学带隙由大块的0.7eV展宽到1.8-2.1eV,并且带隙展宽随着尺寸的减小而进一步增大。高温金属相的VO2纳米颗粒,不同于大块VO2单晶和薄膜,存在460nm附近的半宽度约为50nm的消光峰,以及在近红外光区的峰位置约为1600nm、半宽度达1000nm以上的强消光峰,分别与表面等离激元的多极子共振模与偶极共振模相关。并且前者随纳米粒子尺寸的增大而红移,而后者则随纳米粒子尺寸的增大而蓝移。20nm的VO2纳米颗粒的光学热滞回线,其金属-半导体相变过程跨越15K的温度区域,升温-降温过程滞后约25K。随着纳米颗粒尺寸的减小,迟滞回线宽度减小,相变温度也降低。VO2纳米颗粒薄膜呈现出显著的光学开关效应,在近红外光区,通过表面等离激元共振,透射率动态范围达到2.63。与光学热滞回线对比,加热时的电学热滞回线的相变起始温度低于光学热滞回线约5K,起源于VO2纳米颗粒点阵中光学性质与电学性质的金属-绝缘体转变具有不同的机制：光学过程由孤立纳米粒子的金属-半导体转变所主导；而电学过程则是由纳米粒子本身的金属-半导体转变和点阵整体的金属-绝缘体转变所共同支配。通过对变温Ⅰ-Ⅴ曲线的分析,确定出相变前后VO2纳米颗粒薄膜的电荷传导均满足Schottky机制。更多还原

【Abstract】 Vanadium dioxide undergoes a first-order phase transition from a low-temperature monoclinic semiconductor to a high-temperature rutile metal at about 340K. This transition is accompanied by sharp changes in resistivity, transmission and reflectivity in near-IR. Thermal expansion causes damage to the bulk VO2 through the semiconductor-to-metal phase transition (SMPT), but thin films and nanoparticle arrays are tolerant to repeat the heating cycle.In this paper, we used the Ultra High Vacuum Cluster Beam System (UHV-CBS) to deposit the low-energy clusters by means of magnetron plasma gas aggregation to fabricate vanadium oxide nanoparticle films. At room temperature, optical band gap of VO2 nanoparticles expanded to 1.8-2.1eV from 0.7eV (bulk) and increased as the particle size decreased because of quantum confinement effect. Above Tc, the metal VO2 nanoparticles, different from bulk and films, exhibited an extinction peak near 460nm (FWHM=50nm) and another one at near-IR 1600nm (FWHM>1000nm), caused respectively by multipole resonant mode and dipole resonant mode of surface plasmon. The foremer red-shifted as particle size rised, while the latter blue-shifted. In VO2 nanoparticles (particle size 20nm), the thermal hysteresis width was about 20K and the phase transition went across 15K. Both of the hysteresis width and phase-transition temperature were reduced as particle size decreased. Optial switching in VO2 nanoparticle films had the transimission change DT=Tmax/Tmin=2.63, caused by near infrared surface plasmon resonance. The beginning temperature of the SMPT in electrical property was 5K lower than that in optical, indicating two different mechanisms of the SMPT in VO2 nanoparticle arrays, that is, the optical phase transiton was dominated by phase transition in VO2 single nanoparticle, but the electrical phase transiton was related to the phase transiton both in singe nanoparticle and the whole nanoparticle arrays. After analyzing theⅠ-Ⅴcurve at different temperature, we concluded the charge transport mechanism in VO2 nanoparticle films was Schotty mechanism before and after the phase transition.更多还原