表面等离子共振双光束差分研究和数值模拟

为提高光强调制型表面等离子共振传感器的灵敏度和抗干扰能力,本文提出了一种采用双光束差分光强的SPR检测新方法.通过对该方法的理论计算和数值模拟分析,得到了不同入射角和不同金膜厚度时,反射光强差与样品折射率之间的关系曲线.研究表明,与传统的光强调制方法相比,当两束光入射角相差5°,金膜厚度在40～50 nm时,该方法是有更高的灵敏度和更宽的测量范围,并且由于采用了光强差分技术,大大提高了传感器的抗干扰性和稳定性.     

表面等离子共振氢气传感研究进展

基于表面等离子共振原理的光学氢气传感已经成为氢气传感技术研究的热点.表面等离子共振传感器具有安全可靠、灵敏度高、实时性好、便于分布式多点检测等优点,在氢气泄漏检测方向具有广阔的应用前景.本综述介绍了表面等离子共振氢气传感器的三种主要结构类型:棱镜耦合结构,光栅耦合结构和光纤耦合结构的检测原理、典型结构及其研究进展;重点论述了表面等离子共振氢气传感技术中氢敏感膜系的研究现状和技术难题;分析了目前表面等离子共振氢气传感实际应用所面临的瓶颈,并对未来的研究方向进行了展望.结合实际,提出了开发基于光纤微结构和纳米材料的新型氢气传感器件,并且将传感原理延伸至局域表面等离子体共振,表面等离子体共振成像等新兴技术.     

纳米多孔光波导漏模共振传感器的折射率灵敏度分析(英文)

在玻璃基片上射频溅射50 nm厚的金膜,然后利用TiO2胶体溶液在金膜表面制备了厚度约为320 nm的TiO2纳米多孔薄膜.以此双层膜为漏模光波导芯片,构建了基于Kretschmann结构的波长调制型光波导漏模共振(LMR)传感器.利用扫描电子显微镜(SEM)观测了TiO2纳米多孔薄膜的表面和横截面形貌.实验研究了在纳米多孔光波导中给定漏模的共振波长及折射率灵敏度与入射角的依赖关系.结果表明,随着入射角的增大,共振波长逐渐蓝移,折射率灵敏度随之下降.此外,与传统的表面等离子体共振(SPR)传感器进行了对比,结果表明在相同的共振波长下,纳米多孔光波导LMR传感器折射率灵敏度大于SPR传感器.     

贵金属Pd离子掺杂纳米ZnSnO3的氢敏性能及掺杂机理

为了提高ZnSnO3的氢敏性能,以共沉淀法制备ZnSnO3并对其进行了贵金属Pd2＋掺杂.采用X射线衍射仪（X-ray diffraction,XRD）及透射电镜（transmission electron microscopy,TEM）对制备的气敏材料进行结构及形貌表征,并使用静态配气法测试了掺杂前后ZnSnO3的氢敏性能.结果表明：掺杂Pd2＋可显著提高ZnSnO3的氢敏性能.在工作温度为240℃、浓度为300×10-6的条件下,Pd2＋掺杂纳米ZnSnO3对氢气的灵敏度为12,是未掺杂时的3倍.基于第一性原理探讨气敏机理,计算结果表明：Pd2＋掺杂改变了ZnSnO3能带间的电子运动状态,使ZnSnO3费米能级由0.725 eV移动到1.035 eV,在费米能级附近产生新的电子峰,使其电导性能在气敏反应过程中改变更为明显.Pd2＋掺杂还使ZnSnO3表面吸附氧的能力显著增加,对提高氢敏性能起到了关键作用.     

SnO2纳米薄膜氢敏特性的研究

采用溶胶-凝胶法制备了SnO2氢敏纳米薄膜.将0.1和0.05mol/L的SnO2溶胶溶液旋涂在Au叉指电极衬底而制得.通过测量在不同温度下SnO2纳米氢敏薄膜的电阻信号来表征其氢敏特性.当温度为250℃时,试样的灵敏度较低,并且响应时间也比较长.温度为300℃时试样的灵敏度较高,响应时间也明显缩短.0.05mol/L溶胶溶液旋涂10层制备的样品在300℃氢气浓度为2.0×10-3时,灵敏度达到了178,响应时间为3.5s.同时实验还发现试样对氢气的响应时间随着氢气浓度的增加先增大再减小.     

金纳米锥阵列与金薄膜耦合结构表面等离子体折射率传感研究

设计了基于SiO₂薄膜间隔的金纳米锥与金薄膜耦合结构表面等离子体共振折射率传感器。使用时域有限差分法研究了复合结构中的表面等离子体共振模式,复合结构不仅能够激发局域表面等离子体共振,也可激发传播表面等离子体共振。入射电磁波的能量部分通过单个金纳米锥耦合到局域表面等离子体,部分通过金纳米锥阵列二维光栅耦合到传播表面等离子体。在待测物折射率1.30～1.40的范围内,对复合结构的反射光谱进行了模拟研究,发现共振波长与分析物折射率呈线性关系,且由于局域和传播表面等离子体的高效激发,反射光谱共振峰处的反射率几乎为零。此外,在最优的金纳米锥几何参数下,传播表面等离子体共振模式的半高全宽非常窄,灵敏度和品质因数分别达到770 nm/RIU和113 RIU^-1,具有良好的折射率传感性能。所设计的复合结构作为表面等离子体共振传感器有望广泛应用于生物检测领域。     

表面等离子共振法测量纳米级金属薄膜厚度数值分析（英文）

针对纳米级金属薄膜厚度测量的需求,建立了基于表面等离子共振(SPR)法膜厚测量的数学模型,并以K9棱镜-金膜-空气组成的Kretschmann结构为耦合装置,对SPR方法的光强、相位、波长、角度4种调制模式进行数值分析,介绍了这4种调制模式的原理,并对其传感器的测量范围、灵敏度等参数进行了分析.结果表明:光强型SPR装置的测量范围最大,相位型SPR装置的灵敏度最高.在实际金属薄膜厚度测量的应用中,除了传感器的测量范围和灵敏度外,还需考虑其后续处理装置、算法的复杂性及性价比,结合诸多因素选择合适的SPR传感器.     

氧化钨厚膜气敏传感器的气氛改性研究

采用丝网印刷法将钨酸分解得到的氧化钨粉末制备成氧化钨厚膜气敏传感器,并先后在氢气和空气气氛中进行还原和氧化处理,系统研究了氢气浓度和氧化时的升温速率对敏感膜的形貌、结构和CO气敏性能的影响.结果表明,经氢气还原-空气氧化后,敏感膜表面形貌由近似球形的颗粒转化为表面光滑两端开口的集束棒状或规则的四方柱状,而晶体结构则没有发生改变.敏感膜对CO的灵敏度(Rair/RCO)随CO浓度的增加和测试温度的升高而增大.与没有进行气氛改性的敏感膜相比,经10%H2气氛还原并在600℃空气中以5℃/min氧化处理后的敏感膜对CO具有最大的灵敏度,其对3.8×10-5CO的灵敏度提高了13.3倍.即通过对敏感膜进行气氛改性可显著提高对CO的敏感性能.     

SnO2修饰MoS2薄膜的n-p可调室温氢气响应及其原位SKPM研究(英文)

研发高性能氢气传感器对氢能及相关产业发展具有重要意义.2D-MoS₂纳米材料在构建快速可靠的室温氢气传感器方面优势显著,但灵敏度和选择性较差.本文报导了具有n-p可调型氢敏响应行为的SnO₂修饰MoS₂薄膜,其原位SKPM研究表明SnO₂(0.38 eV)和MoS₂(0.26 eV)在氢敏响应中会出现不同的表面电势变化,使其界面势垒随SnO₂覆盖率的增加而改变,从而使界面效应对体系n型氢敏响应的积极贡献转变为负面补偿.当SnO₂覆盖率为6.4%时,传感器具有增敏、提速且选择性好的n型氢敏响应,当其提高至95.6%时呈现p型响应.这种随结构n-p可调的氢敏响应既能用于传感层的敏感性能调节,还可为MoS₂基二维材料的气敏响应类型调控提供简单易行、成本低廉的方法.     

LaNi5合金膜退火后的表面结构和氢敏特性

通过在空气中退火来改善由磁控溅射方法制备的LaNi_5合金膜的表面结构,使其具有在室温下吸放氢的能力。借助原子力显微镜、X射线衍射和X射线光电子能谱,分析了LaNi_5合金膜退火前后的形貌、结构和表层成分。结果表明:在空气中退火后,LaNi_5合金膜比表面积增加,并在其表层形成了La_2O_3-Ni的表层结构。氢敏测试结果显示,在空气中退火的样品不需要在高压纯氢中活化,在室温下即对氢气响应,说明该合金膜可以作为氢气传感器的敏感层。     

Suppression of phase transitions in Pd thin films by insertion of a Ti buffer layer

We investigated the effects of a thin titanium (Ti) buffer layer on structural changes and electrical responses of palladium (Pd) thin films. A Ti buffer layer was inserted between a Pd film and the substrate, with varying thickness from 0.5 to 80 nm. Unlike pure Pd films, Ti-buffered Pd films showed no structural deformations after cyclic exposure to hydrogen gas, leading to a linear relationship between sensitivity and hydrogen gas concentration over the measured concentration range of 0 to 2%. This was attributed to the suppression of phase transitions from the α to the β phase in Pd films, due to the reinforced film adhesion by the inserted Ti layer. Our results highlight the practical usability of Pd thin films as reliable and sensible hydrogen sensors, enabled simply by the insertion of a thin Ti buffer layer.     

Optical properties and instrumental performance of thin gold films near the surface plasmon resonance

The optical properties of very thin gold films have been evaluated by Fresnel analysis, with optical boundary conditions pertaining to the surface plasmon resonance (SPR) at the gold-water interface. The experimental SPR characteristic was evaluated in the angular interrogation mode. Film morphology was characterized by high resolution transmission electron microscopy. The magnitude of the resonance, i.e., the SPR signal, sensitively depends on, and is affected by film thickness and morphology. A sharply defined thickness of 55 ± 5 nm is required, to achieve optimum SPR excitation conditions, and instrumental sensitivity. With decreasing film thickness, below 40 nm, the resonance angle starts to shift to larger values. A substantial increase of the intrinsic resonance broadening parameter is observed below 70 nm, associated with an increasingly asymmetric SPR line shape. A similar effect occurs in the presence of a very thin chromium adhesion layer. Surface roughness and film thickness modulations determine the experimentally observed line broadening parameter. Instrumental noise levels largely depend on accuracy and quality at which the resonance angle can be determined. Substantial improvement and instrumental sub-pixel resolution is achievable by optimum fitting routines, accounting for drastic noise reduction and improved instrumental sensitivity, up to two orders of magnitude over the inherent geometric sensor pixel resolution.     

Room temperature hydrogen gas sensitivity of nanocrystalline pure tin oxide

Nanocrystalline (6-8 nm) tin oxide (SnO2) thin film (100-150 nm) sensor is synthesized via sol-gel dip-coating process. The thin film is characterized using focused ion-beam microscopy (FIB) and high-resolution transmission electron microscopy (HRTEM) techniques to determine the film thickness and the nanocrystallite size. The utilization of nanocrystalline pure-SnO2 thin film to sense a typical reducing gas such as hydrogen, at room temperature, is demonstrated in this investigation. The grain growth behavior of nanocrystalline pure-SnO2 is analyzed, which shows very low activation energy (9 kJ/mol) for the grain growth within the nanocrystallite size range of 3-20 nm. This low activation energy value is correlated, via excess oxygen-ion vacancy concentration, with the room temperature hydrogen gas sensitivity of the nanocrystalline pure-SnO2 thin film sensor.     

金属涂层SPR的单端面LPFG折射率传感器(英文)

提出了一种新型的单端面反射的镀有金属膜的长周期光纤光栅传感器.这种基于表面等离子体谐振的具有三层结构的传感器分为两个部分,光栅部分用连续CO2激光脉冲制作,金属膜是由真空镀膜制成.在光栅上镀上各种不同厚度的薄金属膜来激发表面等离子体波,用这种光纤光栅传感器来测量液体的折射率,并研究它的反射谐振谱的特性.在标准气压下,镀有80 nm银膜的光栅从水(ns=1.33)到酒精(ns=1.36)中光栅谐振波长改变了1.14nm,其敏感度达到折射率变化～5×10-4谐振波长改变20 pm.研究发现不同厚度的不同金属膜显示了不同的敏感度.通过比较光栅在空气,水,酒精,甘油,以及在它们的混合物溶液中的谐振波长,得到这种反射式的长周期光纤光栅传感器的敏感特性.为制作一种高性能的用来测量折射率的光纤光栅传感器提供了一个有益的参考.     

New hydrogen sensor based on sputtered Mg-Ni alloy thin film

Pd-capped magnesium-nickel alloy thin films were prepared by magnetron sputtering and their hydrogen sensing properties were investigated. By monitoring the resistance change or the transmittance change of the film, we can obtain the information on hydrogen concentration in air. The sensing range of this sensor is quite wide and it can measure the hydrogen concentration range from 10 ppm to 10% without heating. Using a certain protective coating, the durability of the film can be much improved. Also there is a unique application of Pd/Mg-Ni thin film as ‘hydrogen check sheet’, which can visualize the hydrogen flow.     

Surface-plasmon-resonance-based fiber-optic refractive index sensor: sensitivity enhancement

We have experimentally studied the surface plasmon resonance (SPR)-based fiber-optic refractive index sensor incorporating a high-index dielectric layer using the wavelength interrogation method. Silver and gold have been used as SPR active metals followed by a high-index dielectric layer of silicon. Experimental results predict a redshift in the resonance wavelength with the increase in the refractive index of the sensing layer for a given thickness of the silicon layer. Further, as the thickness of the silicon layer increases, the sensitivity of the sensor increases. The upper limit of the silicon film thickness for the enhancement of the sensitivity has been found to be around 10 nm. The experimental results obtained on sensitivity match qualitatively with the theoretical results obtained using the N-layer model and the ray approach. The increase in sensitivity is due to the increase in the electric field intensity at the silicon-sensing-region interface. In addition to an increase in sensitivity, the silicon layer can be used to tune the resonance wavelength and can protect the metal layer from oxidation and hence can improve the durability of the probe.     

Indium oxide thin film based ammonia gas and ethanol vapour sensor

A sensor for ammonia gas and ethanol vapour has been fabricated using indium oxide thin film as sensing layer and indium tin oxide thin film encapsulated in poly(methyl methacrylate) (PMMA) as a miniature heater. For the fabrication of miniature heater indium tin oxide thin film was grown on special high temperature corning glass substrate by flash evaporation method. Gold was deposited on the film using thermal evaporation technique under high vacuum. The film was then annealed at 700 K for an hour. The thermocouple attached on sensing surface measures the appropriate operating temperature. The thin film gas sensor for ammonia was operated at different concentrations in the temperature range 323–493 K. At 473 K the sensitivity of the sensor was found to be saturate. The detrimental effect of humidity on ammonia sensing is removed by intermittent periodic heating of the sensor at the two temperatures 323K and 448 K, respectively. The indium oxide ethanol vapour sensor operated at fixed concentration of 400 ppm in the temperature range 293–393 K. Above 373 K, the sensor conductance was found to be saturate. With various thicknesses from 150–300 nm of indium oxide sensor there was no variation in the sensitivity measurements of ethanol vapour. The block diagram of circuits for detecting the ammonia gas and ethanol vapour has been included in this paper.     

Material and sensing properties of Pd-deposited WO3 thin films

The physicochemical and electrical properties of Pd-deposited WO3 thin films were investigated as a function of Pd thickness, annealing temperature, and operating temperature for application as a hydrogen gas sensor. WO3 thin films were deposited on an insulating material using a thermal evaporator. X-ray diffractometry (XRD), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) were used to evaluate the crystal structure, microstructure, surface roughness, and chemical property of the films, respectively. The deposited films grew into polycrystalline WO3 with a rhombohedral structure after annealing at 500 degrees C. Adding Pd had no effect on the crystallinity, but suppressed the growth of WO3 grains. The Pd was scattered as isolated small spherical particles of PdO2 on the WO3 thin film after annealing at 500 degrees C, while it agglomerated as irregular large particles or diffused into the WO3 after annealing at 600 degrees C. PdO2 reduction under H2 and reoxidation under air were dependent on both the Pd deposition thickness and annealing conditions. The WO3 thin film with a 2-nm-thick Pd deposit showed a good response and recovery to H2 gas at a 250 degrees C operating temperature.     

Determination of hydrogen absorption in Pd coated Al thin films

Al films, 80–85 nm in thickness and 10–30 μΩ cm in resistivity, are coated with Pd (8–40 nm). The bilayer is exposed to a hydrogen atmosphere of up to 4.0 kPa. The hydrogen concentration is calculated from the frequency change in a quartz crystal microbalance and the electrical resistance of the Pd film, the Al film and the bilayer is measured as function of hydrogen pressure. Concentration and resistance measurements indicate that the Pd coating enables the Al films to absorb hydrogen from the gas phase.