WO3薄膜气敏光学传感特性研究

WO3薄膜是良好的光学气敏传感器材料.采用溶胶凝胶法制备了WO3掺杂薄膜,对样品在不同浓度氢气气氛中的气敏光学性质、敏感度及响应时间进行了测试、分析和计算,并结合光传输理论给出了气敏薄膜的光学变化机制,理论分析与实验结论吻合.     

WO3纳米薄膜的制备与气致变色特性研究

报道了以钨粉为原料，采用溶胶一凝胶技术和旋转镀膜方法，制备出了气致变色WO3纳米薄膜。采用椭偏仪、X射线衍射仪(XRD)、场发射扫描电子显微镜(FE-SEM)、红外光谱仪以及可见光分光光度计等方法分析了薄膜的特性。研究结果表明热处理使得薄膜致密，折射率增大，厚度减小，薄膜结晶；过氧键消失，WO3微结构发生了变化，共角W-O-W键吸收越来越强，且向高波数方向移动。这些变化归因于热处理导致的WO3颗粒形状、团聚状态的变化以及应变键的产生。WO3纳米薄膜具有很好的气致变色特性，致色与退色态透射率变化超过60％，变色起因于H扩散到WO3薄膜中形成的小极化子吸收。     

水对纳米掺钯WO3薄膜气致变色性能的影响

以W粉为原材料,通过溶胶凝胶法结合提拉镀膜法制备了掺钯的气致变色WO3纳米多孔薄膜,并采用不同温度对该薄膜进行了热处理;最后制作成简易的气致变色窗。分别采用傅立叶红外光谱仪(FT-IR)、原子力显微镜(AFM)表征了薄膜中水的存在和薄膜的表面形貌,采用紫外/可见/近红外分光光度计对薄膜致褪色过程的透射率随时间的变化进行原位动态的测试,分析了不同阶段的水的存在对薄膜气致变色性能的影响。研究结果表明:随着气致变色循环次数的增加,薄膜生成水逐渐增加,破坏了薄膜的表面结构,堵塞了薄膜的孔洞,使薄膜气致变色时间延长,但不影响薄膜的致色深度;环境吸附水对薄膜有毒化作用,既延长了薄膜的气致变色的时间也使气致变色深度降低;而适量的薄膜结构水的存在有利于提高薄膜的气致变色速率。     

Structure and optical properties of WO3 thin films prepared by chemical vapour deposition

The structure and optical properties of polycrystalline WO₃ thin films, prepared by annealing of black tungsten layers produced by chemical vapour deposition onto fused quartz substrates, were determined. Three different annealing modes were used. X-ray diffraction spectra revealed that all the films consisted of WO₃ crystallized in the monoclinic form. The optical constants (n and k), the thickness and the density of the films were determined. The optical constants and the density varied as a function of annealing conditions and film thickness.The determined values of the optical constants and the film densities are in agreement with the results found in the literature.Electrochromism was observed in these compounds.     

Material properties of Au-Pd thin alloy films

Thin films of Au-Pd of varying composition were formed by electron beam physical vapor deposition. They were characterized and their application as optical hydrogen sensors was studied. In addition, parameters of sensing performance such as Pd deficiency during deposition, grain size, compositional homogeneity, and the appearance of a natural buffer layer, were examined. Following deposition, Au-Pd films exhibited high atomic intermixing, and a PdO_x buffer layer formed spontaneously. This layer makes it possible to increase film thickness, which improves the intensity of the detecting signal. Accordingly, the suggested deposition method may optimize recent efforts to use Au20 wt.%-Pd thin alloy film in optical hydrogen sensors.     

Vacuum temperature-dependent ellipsometric studies on WO3 thin films

Vacuum temperature-dependent ellipsometric studies on WO(3) thin films are reported at a single wavelength, lambda = 0.633 mum, and across a temperature range of 100 < T 相似文献   

Hierarchical WO3 porous microspheres and their sensing properties

Materials with porous and hierarchical structures are of great interest for potential use in energy and environmental applications. Here, we fabricate the WO₃ microspheres which consist of the nanosheets by using a simple hydrothermal process. The likely formation mechanism of the porous microspheres is proposed based on the time-dependent experiments. As a consequence of the unique hierarchical and porous architecture, the microspheres show excellent gas sensing properties due to their large amount of petals and pores, which benefited for the gas diffusion.     

WO3 thin film prepared by PECVD technique and its gas sensing properties to NO2

Tungsten oxide films have been successfully fabricated from tungsten oxychloride (WOCl₄) precursor by using plasma enhanced vapor deposition (PECVD) technique. The films were deposited onto silicon substrates and ceramic tubes maintained at 100°C under a constant operating pressure of He-O₂ gas mixtures. The compositions and the structures of the thin films have been investigated by means of anaysis methods, such as XRD, XPS, UV and IR. The as-deposited WO₃ thin films were amorphous state and became crystalline after annealing above 400°C. The surface analysis of the films indicates that stoichiometry O/W is 2.77 : 1. The gas sensing measurements of the WO₃ thin film sensors indicate that these sensors have a high sensitivity, excellent selectivity and quick response behavior to NO₂.     

Characterisation and optical vapour sensing properties of PMMA thin films

The present article reports on the characterisation of spin coated thin films of poly (methyl methacrylate) (PMMA) for their use in organic vapour sensing application. Thin film properties of PMMA are studied by UV–visible spectroscopy, atomic force microscopy and surface plasmon resonance (SPR) technique. Results obtained show that homogeneous thin films with thickness in the range between 6 and 15 nm have been successfully prepared when films were spun at speeds between 1000?5000 rpm. Using SPR technique, the sensing properties of the spun films were studied on exposures to several halohydrocarbons including chloroform, dichloromethane and trichloroethylene. Data from measured kinetic response have been used to evaluate the sensitivity of the studied films to the various analyte molecules in terms of normalised response (%) per unit concentration (ppm). The highest PMMA film sensitivity of 0.067 normalised response per ppm was observed for chloroform vapour, for films spun at 1000 rpm. The high film's sensitivity to chloroform vapour was ascribed mainly to its solubility parameter and molar volume values. Effect of film thickness on the vapour sensing properties is also discussed.     

Nanocrystalline ZnO thin films: optoelectronic and gas sensing properties

Nanocrystalline Zinc oxide thin films have been deposited by sol–gel spin coating technique and then have been analyzed before and after a suitable thermal annealing in order to test their applications in various reducing and oxidizing gases. ZnO thin films were highly sensitive and selective for NH₃ gas. The spectrophotometric and conductivity measurements have been performed in order to determine the optical and electrical properties of zinc oxide thin films. The structure and the morphology of such material have been investigated by high resolution electron microscopy and small area electron diffraction. The average particle size is in 60–70 nm.     

Optical properties and sensing applications of lithium iron phosphate thin films

A composite optical waveguide sensor, consisting of lithium iron phosphate (LiFePO₄, LFP) as the sensing material, was constructed and utilized for the detection of volatile organic compound gases. Nano-LFP powder was prepared via the hydrothermal method and was subsequently utilized in a dip-coating procedure for the fabrication of LFP thin films. The effect of heat treating temperature on the refractive index of the thin films was studied. A glass optical waveguide gas sensor was fabricated by coating an LFP thin film on the surface of single-mode tin-diffused glass optical waveguide. The sensor was found to exhibit a linear response to xylene in the range of 50-1000 ppm, with response times of less than 5 s.     

Electrical sensing properties of silica aerogel thin films to humidity

Mesoporous silica aerogel thin films have been fabricated by dip coating of sol-gel derived silica colloid on gold electrode-patterned alumina substrates followed by supercritical drying. They were evaluated as the sensor elements at relative humidity 20-90% and temperature 15-35 °C under an electrical field of frequency 1-100 kHz. Film thickness and pore structure were two main parameters that determined the sensor performance. The film with a greater thickness showed a stronger dielectric characteristic when moisture abounded, and presented a smaller hysteresis loop and a higher recovery rate, due to the large size of pore throats. As the film thickness decreased, at low humidity the surface conductivity enhanced and the response rate increased. The silica aerogel based humidity sensor can be modeled as an equivalent electrical circuit composed of a resistor and a capacitor in parallel, and is driven by ionic conduction with charged proton carriers.     

Structural properties of TiO2–WO3 thin films prepared by r.f. sputtering

TiO₂–WO₃ thin films were prepared by radio frequency (r.f.) reactive sputtering from metallic target. Structural and morphological properties of the thin films have been studied through X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The influence of the annealing on the phase composition TiO₂–WO₃ system was studied. The binding energies of titanium and tungsten are characteristic for Ti⁴⁺ and W⁶⁺. The influence of tungsten on anatase–rutile phase transition in TiO₂ was observed. The structural modeling has been performed to account the preferred orientation in tungsten doped titanium oxide.     

Electrical properties and morphology of obliquely deposited electrochromic WO3 films

A thin film of WO₃ deposited obliquely (θ≈50°) improves the electro-optical response times of an electrochromic display device based on a proton insertion-extraction mechanism. The difference in the response times is attributed to morphological differences as revealed by electron microscope observations. WO₃ films were deposited normally and obliquely, by electron beam gun deposition technique so as to have comparable resistivities in vacuum of about 10^-4 Torr. The resistivity of these films was varied in different ways by exposure to atmospheric air in a controlled manner. Systematic and comparative investigations of the variation in resistivity of these films showed that the resistivity increased in the first stage (10^-4 Torr to atmospheric pressure), attained a maximum value and decreased thereafter in the second stage on long exposure to the atmosphere. The initial increase was explained as the result of oxidation leading to better stoichiometry, limited by the process of uptake of water vapour (hydration). The latter effect was much less for normally deposited film; however, for obliquely deposited film it was much greater and resulted in a decrease in resistivity by three orders of magnitude more than for normally deposited film. The large degree of hydration in an obliquely deposited film was ascribed to its more porous nature, leading to faster electro-optical response times. It was concluded that the microstructure, the stoichiometry and the water content control the electro-optical response of WO₃ films.     

热处理对WO3薄膜光学性质的影响

直流反应磁控溅射法制备了WO3薄膜,薄膜在723K纯N2气中被退火处理.热处理前WO3薄膜为无定形态,热处理后为多晶态.采用透射谱和单谐振子模型获得了薄膜的折射率和消光系数,得到退火前后谐振子能量分别为5.77和5.28eV,色散能为19.9和15.9eV.分析表明退火前后吸收边附近均表现出间接带隙的两段线性关系,间接带隙分别为3.14和2.96eV,声子能量为32和149meV,退火后带隙减小推测可能是由于退火薄膜晶化,氧填隙粒子导致的带尾态效应消失的结果.