Sensors for combustible gas components using modified single crystal zeolites

Single crystals of Heulandite- (HEU) type zeolites were characterized for phase homogeneity (XRD), morphology, chemical composition (SEM/EDX) and thermal stability (DTA). Afterwards the crystals were ion-exchanged against Ag and Cu in order to obtain defined starting materials for sensor applications. AC conductivity type sensors were constructed using ion-exchanged stilbite (HEU-type zeolite) as gas sensitive solid electrolyte with sputtered Au as electrode material. Temperature dependent conductivity measurements showed activation energies for the ionic motion between 0.54 and 0.76 eV. Ag-ion exchanged stilbites were applied as gas sensing materials in the temperature interval between 60 °C and 105 °C under defined H₂O concentrations and revealed stable signals with regard to different gaseous aliphatic components (mixtures with pure nitrogen or synthetic air). It could be shown that the sensor behaviour was affected by the polarity of the aliphatic molecules and their specific interaction with the ions and molecules of the channels within the zeolites lattice. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997     

Proposal for a simple integrated optical ion-exchange waveguide polarizer with a liquid crystal overlay

A simple, compact electro-optic polarizer based on an ion-exchanged glass channel waveguide covered with a nematic liquid crystal (LC) is proposed. A full-vectorial beam propagation method is employed to simulate this device for the first time. For the cases of zero and strong LC surface anchoring, the performance of the proposed polarizer under different applied voltages is analyzed numerically. Analysis indicates that surface anchoring of the liquid crystal is a key issue influencing the performance for the proposed optical polarizer device.     

玻璃波导及两次离子交换法

本文报道Soda-lime玻璃的Ag~+-Na~+和K~+-Na~+离子交换波导的制备、特性分析;并介绍制作表面折射率元件(例如棱镜、透镜)的两次离子交换法,以及用卢瑟福后向散射谱分析玻璃离子交换后表面层的离子分布轮廓。     

Ionic conduction and dielectric relaxation in Ag/Na ion-exchanged aluminosilicate glasses: mixed mobile ion effect and KWW relaxation

Ag⁺/Na⁺ ion-exchanged aluminosilicate glasses with uniform concentration profiles were prepared, and their electrical conductivities were investigated as functions of the ion-exchange ratio and the initial glass compositions. In the case of the ion-exchanged glasses of x20Ag₂O–(1−x)20Na₂O–10Al₂O₃–70SiO₂ in mol%, the conductivity, σ, and its activation energy, E_σ, showed a minimum and a maximum at the same ion-exchange ratio x=0.3, respectively, and the mixed mobile ion effect (MMIE) was observed. The fully ion-exchanged sample attained σ=3.5×10⁻⁵ S/cm at 200 °C, which was 1.5 orders of magnitude larger than that of initial glass. In the case of x25Ag₂O–(1−x)25Na₂O–25Al₂O₃–50SiO₂, the mixed mobile ion effect was also observed at x=0.5. The maximum conductivity of 2×10⁻⁴ S/cm at 200 °C was obtained in the fully ion-exchanged glass sample.

The electric relaxation analysis was also conducted on both systems, and Kohlrausch–Williams–Watts (KWW) fractional exponent β was obtained as a function of x. The decrease of β was observed near x≈0.3 in the former system, while that of the later system was independent of the ion-exchange ratio. Based on the structural analysis results, the observed behaviors were investigated from the point of view of the occupation of Ag⁺ ions on the non-bridging oxygen-site (NBO-site) and the charge compensation-site (CC-site) of AlO₄ tetrahedral unit.     

掩埋型离子交换玻璃光波导的变分分析

用变分法对离子交换法制备的掺铒光波导的传播特性进行了分析,推导出了适用于掩埋型离子交换玻璃沟道光波导中场分布传播常量的变分表达式,构建了场分布的厄米-高斯型试探解,在两种不同实验条件下,采用变分法确定了试探解中的待定参量,获得光波导中的场分布,利用传播常量的变分公式和已确定的场分布计算得到了传播常量和有效折射率。计算数据表明:导波区域的有效折射率稍稍地大于限制层的折射率,说明离子交换法制备的波导器件是弱波导;高的辅助退火电场强度和适当的退火时间下,所制备的光波导可以支持更多光模式的传输。该方法计算过程简洁、快速,计算结果与实验结果吻合。     

掺铒碲-钨-钠玻璃基质的光谱性质研究

制备了用于离子交换法制备光波导器件的掺铒碲-钨-钠玻璃基质。应用扎得-奥菲而特(Judd—Ofelt)理论计算了玻璃样品的三个强度参量,由强度参量计算了Er^3 离子的自发跃迁几率、荧光分支比等光谱参量;应用麦克库玻(McCumber)理论,计算了Er^3 离子在1．5μm的受激发射截面,荧光测试发现Er^3 离子的荧光半峰全宽可达65nm。比较了Er^3 离子在不同玻璃基质中的光谱特性。结果表明,Er^3 离子在碲-钨-钠玻璃中具有较高的受激发射截面和较宽的荧光半峰全宽,可以用于宽带光波导器件的制备。     

Research on the influence of fabrication parameters on the performance of buried ion-exchanged glass waveguides using the variational method

The variational method is proposed to analyze the influence of the fabrication parameters on the performance of buried K⁺–Na⁺ ion-exchanged Er³⁺–Yb³⁺ ions co-doped glass waveguide. The unknown parameters of the Hermite–Gaussian functions as the trial field distribution are determined based on the scalar variational principle. It is demonstrated that the results calculated in this paper agree with those measured in the experiment. The mode dimensions, the effective refractive index, and the overlap factor as the functions of the fabrication parameters are investigated. These results of the variational analysis are useful for the design and optimization of Er³⁺–Yb³⁺ ions co-doped waveguides.     

Copper diffusion in ion-exchanged soda-lime glass

Cu-alkali ion exchange in silicate glasses gives rise to a peculiar copper distribution, with the presence of both the Cu²⁺ and Cu⁺ oxidation states. Grazing incidence X-ray absorption near-edge structure spectroscopy and secondary ion mass spectrometry were performed on different ion-exchanged samples. The results show that the Cu²⁺/Cu⁺ ratio is strongly depth-dependent. The relative presence of the two species throughout the exchanged region turns out to be governed by their different diffusion regimes, while the chemistry of the red-ox process is shown to play a minor role. A phenomenological model is proposed to describe the diffusion process. PACS 61.10.Ht; 61.43.Fs; 82.65.+r; 67.80.Mg     

Gas sensing performance of ion-exchanged Y zeolites as an impedimetric ammonia sensor

Zeolites are valuable chemical catalysts and excellent sorbents; several reports have used zeolites for chemical gas sensing. This article systematically investigates the gas sensing performance of ion-exchanged Y zeolites. The interactions between zeolites and ammonia can effectively improve their ionic conductivity, and the zeolites are explored as an impedimetric ammonia sensor. The sensor development was supported by a detailed interpretation of the ammonia-supported ionic conductivity, which was deduced from the measurements of temperature-programmed impedance over a wide temperature range and provides an understanding of the sensing parameters (e.g., temperature and concentration of ammonia). The elevated temperature accelerates the kinetics of the ammonia adsorption/desorption, but it reduces the adsorbing capacity of the zeolite. The thickness of the zeolite pellet is a key parameter for determining the detection limit. Ag-Y and H-Y have higher working temperatures than the alkali cation-exchanged Y zeolite. The excellent selectivity of Ag-Y and Na-Y indicates that they are good candidates as practical ammonia sensors.

     

Determination of refractive index profiles of gradient optical waveguides by ellipsometry

Ag⁺-Na⁺ and K⁺-Na⁺ ion-exchanged optical waveguides in soda-lime glass are characterised by ellipsometry. Refractive index profiles of the waveguides are calculated from ellipsometric multiple angle of incidence data using the Newton-Kantorovitch type iterative procedure and compared with those reconstructed by inverse WKB method. It is demonstrated that such continuous profiles with relatively small index gradient (of the order of 0.1 and 0.01), extending to few micrometers in depth, can be determined by ellipsometric measurements. A good agreement is found between results obtained by ellipsometry and by the inverse WKB method at depths above 500–600 nm, while there is a difference in the subsurface region, where ellipsometry is more sensitive to the quality of the surface. The profiles obtained by the two methods are consistent if the surface thin layer is etched.     

Compact design of 1×16 cascaded Y-branch splitter

We proposed a new kind of cascade Y-branch splitter with a branching region and a fan-out region.The length of the new device are analyzed in detail and compared with ordinary ones.The results show that the new splitter can be 10%-30% shorter than the ordinary splitters.We designed and fabricated a 1× 16 splitter in K+/Na+ ion-exchanged BK7 glass.The length of the new designed splitter is 30-mm,which is 85% of the length of an ordinary splitter.     

Composite optical waveguide composed of a tapered film of bromothymol blue evaporated onto a potassium ion-exchanged waveguide and its application as a guided wave absorption-based ammonia-gas sensor

For what is the first time to our knowledge, we have successfully evaporated a tapered film of bromothymol blue (BTB) onto a potassium ion-exchanged (PIE) waveguide to form a composite optical waveguide (COWG) for trace-ammonia detection. The BTB film has a high refractive index (1.69) and a smooth surface and is transparent to a 633-nm laser beam in air. In the COWG structure, the BTB film serves as a single-mode waveguide, and adiabatic transition of the TE(0) mode was realized between the BTB waveguide and the PIE waveguide with both BTB tapers. In the presence of ammonia, the BTB film changes color from yellow to blue, which causes absorption of the 633-nm guided wave. Our experimental results demonstrate that such a guided wave absorption-based ammonia-gas sensor is much more sensitive than one based on evanescent-wave absorption. A detection limit of part in 10(9) of ammonia has been realized for a BTB film-PIE glass COWG.     

Screen-printed polymer waveguides for integrated optics

We demonstrate screen printing of polymer waveguides on rigid and flexible substrates. The waveguides are characterized by optical microscopy and propagation losses are determined by cut-back measurements. Furthermore, the efficiency of light coupling using fluorescent molecules within the waveguides is measured with regard to the application feasibility in sensor systems. It is shown that minimum propagation losses of 0.74 dB/cm can be reached with this low-cost printing technique.     

应用哈特曼-夏克波前传感器测量大气湍流参数

对非科尔莫戈罗夫（Kolmogorov）湍流情况,在利用哈特曼－夏克（Hartmann-Shack)波前传感器的波前斜率测量原理并结合其时空结构及相关分析的基础上,提出了一种应用斜率结构－相关函数和斜率归一化相关系数测量大气湍流参数β（归一化相位空间功率谱指数下降因子）和ρ0（大气湍流强度）的新方法。利用这种方法对1km激光水平大气传输实验数据进行了分析。     

Active Optical Poly(vinylchloride) Thin-Film Waveguide Ion Sensor

The effectiveness of a proposed PVC (Poly(vinylchloride)) thin-film waveguide ion sensor with high sensitivity which is based on a polymer matrix to measure the concentration of various biochemical ions is assessed. The waveguide is made of PVC co-polymer matrix containing ionophore, dioctylphthalate and chromoionophore, and plays important roles both in light propagation and in selective ion sensing. To evaluate the efficiency of the sensor, standard calcium solution is applied. Results showed the proposed sensor to be very effective as an ion sensor. This active waveguide sensor has the advantages of utilizing both the molecular recognition technique and the waveguide detection technique.     

Numerical study of an ion-exchanged glass waveguide using both two-dimensional and three-dimensional models

A numerical study is carried out to compare the two-dimensional (2-D) case and three-dimensional (3-D) case for the modelling of an ion-exchanged glass waveguide. It is shown that different waveguide widths on the photomask correspond to different ion concentration distributions after an annealing process. A numerical example is presented of two waveguide sections with different widths indicates that due to the abrupt change of the waveguide width, a 3-D theoretical model is required for an accurate prediction of the parameters of ion-exchanged glass waveguides. The good agreement between the modelled and measured results proves that the developed 3-D numerical model can be beneficially utilized in the generalized design of optical devices based on ion-exchange waveguides.     

Investigation of the processes of heat propagation in W/FeSb<Subscript>2</Subscript>/W detection pixel of the single photon thermoelectric detector

The results are presented of the computer modeling of the processes of heat propagation in the single layer detection pixel of the thermoelectric single photon detector after the absorption of photon with the energy of 1–1000 eV. The different geometries of the detection pixel consisting of the tungsten absorber and thermoelectric sensor from the strongly correlated FeSb₂ semiconductor are considered. The differences of temporal dependence of the signal appearing on the sensor for various size of the sensitive pixel elements are studied in detail. The energy resolution and the count rate of the detector are estimated. It is shown that the FeSb₂ sensor of thermoelectric detector provides the generation of significantly higher signal as compared with the CeB₆ sensor and has the perspectives of application in the single photon detectors with the high energy resolution.     

槲皮素包裹修饰硅包银纳米颗粒作为荧光传感器对铜离子的识别作用

制备了一种基于天然产物槲皮素接枝硅包银核壳结构的纳米荧光传感器(Ag@SiO₂@Qc),对铜离子具有好的选择性和灵敏性。Ag@SiO₂@Qc与Cu2+离子结合后,荧光发射强度发生猝灭,并且可通过荧光滴定光谱得到了荧光滴定曲线：y = -32.864x+587.59(R2=0.998),其线性范围分别为：3×10-7~4.8×10-6 mol·L-1,最低检测限为1.0×10-7 mol·L-1。并且将Ag@SiO₂@Qc应用于环境中水样的检测结果的准确度好,精密度高,而且更加环保、方便、快捷,具有很大发展潜力与应用价值。     

Excitonic absorption of spherical PbS nanoparticles in zeolite A

We report the optical and structural properties of PbS nanoparticles in zeolite A. The samples were obtained by sulfidation of the Pb²⁺ ion-exchanged zeolite in a thiourea solution at 50 °C. The optical properties of the samples were studied by diffuse reflectance spectroscopy. Their crystalline structure and morphology were studied by electron diffraction and by transmission and scanning electron microscopy. The results show that the nanoparticles are not inside the zeolite cages but outside, embedded in the zeolite matrix. Exciton absorption peaks at much higher energy than the fundamental absorption edge of bulk PbS indicate quantum confinement effects in the spherical shape nanoparticles as a consequence of their small size.     

新颖的微弯结构Mach-Zehnder干涉仪型传感器及其优化设计

介绍了一种改进的Mach-Zehnder干涉仪型传感器,采用微弯结构波导代替了传统的MZ干涉结构的两臂. 利用三维波束传播法（3D-BPM）对传感器的敏感区域,微弯结构的形状进行了研究,同时研究了微弯结构的振幅和周期对灵敏度的影响,并采用梯度算法对这两个最重要的参数进行综合优化. 模拟结果表明,优化后的传感器敏感度比优化前提高了一倍多.