氧化钒—碳纳米管复合薄膜的制备、表征及光电特性研究

发布时间：2018-03-09 19:56

本文选题：VO_x薄膜　切入点：碳纳米管　出处：《电子科技大学》2017年博士论文　论文类型：学位论文

【摘要】：溶胶凝胶法(Sol-Gel)制备的氧化钒(VO_x)的结构、光学和电学性能已经被广泛研究,然而,迅猛发展的实际应用对材料性能不断提出新的挑战。为了提高该材料的综合性能,基于VO_x的复合材料备受关注,其中,对氧化钒-碳纳米管(VO_x-CNT)复合材料的研究最深入。目前,VO_x-CNT复合材料的研究及应用主要集中在超级电容器和传感器方面,该复合材料在红外探测器中的研究尚未见报道。本文采用Sol-Gel制备了VO_x和VO_x-CNT复合薄膜(2≤x≤2.5),并通过多种材料表征方法对薄膜进行了全面的研究。分析了氧化钒-单壁碳纳米管(VO_x-SWCNT)复合薄膜作为红外探测器热敏材料的可行性。本文的研究内容如下:采用Sol-Gel制备了VO_x薄膜并分析了其形貌、晶态和光电性能。结果表明,退火温度太低、退火时间太短都会导致钒醇盐不能充分分解,无法形成性能优异的VO_x薄膜;而退火温度太高会破坏VO_x的结构、长时间退火会使薄膜被氧化为高价态V2O5,两者都会降低薄膜综合性能。与之相比,310℃退火1 h能够得到综合性能最优的VO_x薄膜,其主要成分为V2O5,并含有少量低价态VO_x,其方阻较低,TCR达到-2.52%K-1、具有较高的吸收率,有望用作微测辐射热计热敏材料。基于Sol-Gel,采用三种不同的薄膜制备方法(混合旋涂、分层旋涂和分层喷涂)制备了VO_x-CNT复合薄膜。不同制备方法和碳纳米管种类会影响VO_x的物理和化学性质。在混合旋涂和分层旋涂制备的复合薄膜中,VO_x与CNT之间的相互作用比较弱,所以通过上述旋涂方式加入CNT对薄膜性能提升较小。对于分层喷涂法,MWCNT与VO_x之间的相互作用比较强烈,由此明显地损坏了VO_x的结构并降低薄膜方阻和TCR;然而,VO_x与SWCNT之间的相互作用适中,因而具有较好的均匀性、适当的方阻和较高的TCR,表现出更优的综合性能。在分层喷涂法制备VO_x-SWCNT的基础上,深入探讨了SWCNT浓度对薄膜性质的影响。结果表明,在复合薄膜中,VO_x与SWCNT之间通过化学作用结合,该相互作用随着碳纳米管浓度的升高而增加,并在浓度约为6 wt%时达到饱和。与之对应,复合薄膜的V=O含量、光学透过率、光学带隙、方阻和TCR均发生规律性变化,并在6 wt%时达到饱和。然而,值得注意的是,复合薄膜的综合性能在碳纳米管浓度约为4 wt%时达到最优,此浓度下的复合薄膜具有良好的微测辐射热计应用前景。进一步使用椭圆偏振技术对Sol-Gel制备的VO_x-SWCNT复合薄膜进行了深入研究。结果表明,5振子Tauc-Lorentz模型可以作为VO_x及VO_x-SWCNT的色散模型。研究发现,使用椭偏仪对复合薄膜进行表征测试得到的薄膜光学带隙、定域态宽度等参数也随着碳纳米管浓度的增加而变化,并出现了与上一章内容类似的饱和现象。此外,还对Tauc-Lorentz模型中不同的振子能量进行了归属,这对于认识VO_x薄膜及VO_x-SWCNT复合薄膜的能带结构,拓展Tauc-Lorentz模型的应用有重要的意义。重要的是,本文还对Sol-Gel制备的不同退火温度下的VO_x薄膜和VO_x-SWCNT复合薄膜的电学性质进行了深入研究。不同退火温度下的VO_x薄膜电导率的EMN为+16 meV,说明其电导率符合Meyer-Neldel Rule(MNR)。然而,当SWCNT加入之后,低温退火(≤310℃)的复合薄膜的EMN为+13 meV,仍然呈现MNR;令人惊奇的是,高温退火(≥310℃)的复合薄膜EMN为-43 meV,出现反MNR现象。最后,对不同浓度VO_x-SWCNT复合薄膜的电学性能进一步研究,结果表明不同碳纳米管浓度的复合薄膜的电导率也出现MNR现象,EMN为+46 meV。本文还对三类薄膜电导率的MNR现象进行了理论分析,这对于认识VO_x和VO_x-SWCNT复合薄膜的电学性能以及深入了解MNR和反MNR现象有重要意义。
[Abstract]:Sol gel method (Sol-Gel) preparation of vanadium oxide (VO_x) structure, optical and electrical properties have been extensively studied, however, the practical application of rapid development and constantly put forward new challenges on the properties of the material. In order to improve the comprehensive performance of the material, composite materials based on VO_x have attracted much attention, which, on oxidation of vanadium carbon nanotubes (VO_x-CNT) composites most deeply. At present, the research and application of VO_x-CNT composite material mainly concentrated in the super capacitor and the sensor, the research of composite material in infrared detector is reported in this paper. The VO_x and VO_x-CNT composite thin films were prepared by Sol-Gel method (x = 2 ~ 2.5), and the films were characterized by various methods of comprehensive research materials. Analysis of vanadium oxide single walled carbon nanotubes (VO_x-SWCNT) composite film as the feasibility of infrared detector sensitive material. The research contents of this paper are as follows: Preparation of VO_x thin films and their morphology were analyzed by Sol-Gel, and the photoelectric properties of crystal. The results show that the annealing temperature is too low, the annealing time is too short will lead to vanadium alkoxide is not fully decomposed, unable to form a VO_x film of good performance; but too high annealing temperature will destroy the VO_x structure, long time annealing will make the film was oxidized to high valence V2O5, both of which reduce the comprehensive properties of the films. Compared with the VO_x thin films annealed at 310 C 1 h can obtain the optimal comprehensive performance, its main composition is V2O5, and contains a small amount of low valence VO_x, the resistance is low, TCR is up to -2.52%K-1, the absorption rate is high. Is expected to be used as micro bolometer thermistor materials. Based on Sol-Gel, using three different film preparation method (mixed spin coating, spin coating and layered layered spraying) VO_x-CNT composite films were prepared. Different preparation methods of carbon nanotubes and the kind of VO_x will affect the matter Physical and chemical properties. The composite film mixed spin coating and layered spin coating preparation, interaction between VO_x and CNT is relatively weak, so the way of adding CNT spin coating on the properties of the films increase smaller. For layered spraying method, interaction between MWCNT and VO_x is relatively strong, thus significantly damaged the structure of VO_x and reduce the sheet resistance and TCR; however, the interaction between VO_x and SWCNT is moderate, so it has good uniformity, proper resistance and higher TCR showed better performance. Based on the preparation of VO_x-SWCNT layered spraying method, discusses the effects of SWCNT concentration on the film nature. The results showed that in the composite films, between VO_x and SWCNT through the combination of chemical action, the interaction increases with the concentration of carbon nanotubes, and at a concentration of about 6 wt%. The corresponding saturated, thin composite The content of V=O film, optical transmittance, optical band gap, square resistance and TCR changes, and at 6 wt% reached saturation. However, it is worth noting that the overall performance of the composite film reached about 4 wt% for the optimal concentration of carbon nanotubes, the composite film has good concentration. The micro bolometer application. VO_x-SWCNT composite films further using ellipsometry on the preparation of Sol-Gel were studied. The results show that the Tauc-Lorentz model can be used as a 5 oscillator dispersion model of VO_x and VO_x-SWCNT. The study found that the composite films were characterized by optical band gap using ellipsometer localized width also changes along with the increase of the concentration of carbon nanotubes, and the emergence of a saturation phenomenon similar to the previous chapters. In addition, the oscillator of different Tauc-Lorentz model energy were assigned, this The band structure of VO_x film and VO_x-SWCNT composite film, has important significance to application of Tauc-Lorentz model. It is important that the electrical properties of VO_x thin films and VO_x-SWCNT composite films with different annealing temperature of the Sol-Gel prepared under studied. VO_x thin film conductivity under different annealing temperatures EMN +16 meV, the electrical conductivity in accordance with Meyer-Neldel Rule (MNR). However, when SWCNT was added after annealing at low temperature (less than or equal to 310 DEG C) composite film EMN +13 meV, is still MNR; surprisingly, high temperature annealing (less than 310 DEG C) composite film EMN -43 meV, anti MNR the phenomenon. Finally, further study on the electrical properties of different concentrations of VO_x-SWCNT composite films, the results show that the conductivity of composite films with different concentration of carbon nanotubes also appeared in MNR EMN +46 meV., the three kinds of films The theoretical analysis of the rate of MNR phenomenon has been carried out, which is of great significance for understanding the electrical properties of VO_x and VO_x-SWCNT composite films as well as in understanding MNR and anti MNR phenomena.

【学位授予单位】：电子科技大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB383.2

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