Cathodoluminescence Depth Profiling in SiO2:Ge Layers

 For investigation of the luminescent center profile cathodoluminescence measurements are used under variation of the primary electron energy E ₀ = 2…30 keV. Applying a constant incident power regime (E ₀·I ₀ = const), the depth profiles of luminescent centers are deduced from the range of the electron energy transfer profiles dE/dx. Thermally grown SiO₂ layers of thickness d = 500 nm have been implanted by Ge⁺-ions of energy 350 keV and doses (0.5–5)10¹⁶ ions/cm². Thus Ge profiles with a concentration maximum of (0.4 – 4) at% at the depth of d_m≅240 nm are expected. Afterwards the layers have been partially annealed up to T _a = 1100 °C for one hour in dry nitrogen. After thermal annealing, not only the typical violet luminescence (λ = 400 nm) of the Ge centers is strongly increased but also the luminescent center profiles are shifted from about 250 nm to 170 nm depth towards the surface. This process should be described by Ge diffusion processes, precipitation and finally Ge nanocluster formation. Additionally, a Ge surface layer is piled-up extending to a depth of roughly 25 nm.     

Preparation and Characteristics of Porous Silica Films by a Modified Base-Catalyzed Sol-Gel Process Containing PVA: II. Film Preparation

Porous SiO₂ films were successfully deposited on silicon substrates by a modified base-catalyzed Sol-Gel process (MBCP) containing polyvinyl alcohol (PVA). The process conditions, such as the gelation time, the synthesis temperature, the stabilizing agent of the precursor solution and the spin coating speed, the heat-treatment, the annealing temperature of the film on the microstructure and porosity of porous SiO₂ films were systematically investigated by SEM, XRD and ellipsometry techniques. This study provides a novel preparation technique for the porous SiO₂ film. Using this process, the resultant film can reach a thickness of 3.6 m for one layer, a porosity of 25–50%, a low thermal conductivity of 0.11 W/m·K. This film will be used as a low dielectric layer, an thermal-insulating layer and a low refractive index layer.     

Azocalixarenes: Synthesis, Characterization, Complexation, Extraction, Absorption Properties and Thermal Behaviours

Azocalixarenes, which have a conjugated chromophore azo (–N=N–) group in p-positions, are synthesized in “one-pot” procedures in satisfactory yields. Their structures in the solid and solution are elucidated by UV–vis, FT-IR, ¹H and ¹³C NMR spectroscopic methods as well as elemental analysis techniques. Some of them are complexed with metal ions (alkali, alkaline-earth and transition metal ions) under neutral conditions. A wide variety of applications is expected by the functionalization of the side arms. The selective liquid–liquid extraction of various alkali, alkaline-earth and transition metal cations from the aqueous phase to the organic phase is carried out by using azocalixarenes. Furthermore, the synthesized azocalixarenes are utilized for selective extraction of Fe³⁺ cations from the aqueous phase to the organic phase. The effects of varying pH and solvent upon the absorption ability of azocalixarenes substituted with electron-donating and electron-withdrawing groups at their o-, m-, p-positions are examined. The thermal behaviours of azocalixarenes containing upper rim functionalized groups are investigated by means of thermogravimetry (TG), differential thermal analysis (DTA) and differential thermogravimetry (DTG).     

Thermal decomposition of ammonium fluoroferrates (NH4)xFeF2x (2≤x≤3)

Different ammonium fluoroferrates (NH₄)_xFeF_2x (2≤x≤3) have been investigated. The thermal decomposition of the compounds obtained can be interpreted by their identical crystal structures (cryolite type). The decomposition products of all ammonium fluoroferrates formed in initial stage are isostructural of NH₄FeF₄. The decomposition is accompanied by the partial reduction of Fe(III) to Fe(II) by ammonium isolated. The end product of the thermal decomposition is FeF₂ and FeF₃ mixture.     

Effect of substituents (NH_2,OH,F) on structures and stability of lithofluorosilylenoids

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Determination of the Thermal Degradation Kinetic Parameters of Carbon Fibre Reinforced Epoxy Using TG

In this work, a kinetic study on the thermal degradation of carbon fibre reinforced epoxy is presented. The degradation is investigated by means of dynamic thermogravimetric analysis (TG) in air and inert atmosphere at heating rates from 0.5 to 20°C min⁻¹ . Curves obtained by TG in air are quite different from those obtained in nitrogen. A three-step loss is observed during dynamic TG in air while mass loss proceeded as a two step process in nitrogen at fast heating rate. To elucidate this difference, a kinetic analysis is carried on. A kinetic model described by the Kissinger method or by the Ozawa method gives the kinetic parameters of the composite decomposition. Apparent activation energy calculated by Kissinger method in oxidative atmosphere for each step is between 40–50 kJ mol⁻¹ upper than E _a calculated in inert atmosphere. The thermo-oxidative degradation illustrated by Ozawa method shows a stable apparent activation energy (E _a ≈130 kJ mol⁻¹ ) even though the thermal degradation in nitrogen flow presents a maximum E _a for 15% mass loss (E _a ≈60 kJ mol⁻¹ ). This revised version was published online in July 2006 with corrections to the Cover Date.     

Curing of a maleimide model compound

A monofunctional maleimide-ended model compound was synthesized and purified. The thermal curing of this compound was followed by size exclusion chromatography and the molecular masses of the oligomers formed during the curing reaction were determined by mass spectroscopy. It was found that high molecular mass species were not thermally stable. At high temperature and after enough time, a strong decrease in the polydispersity of the oligomers and a significantly preferential formation of trimer were observed. From ¹³C-NMR characterization, a five membered ring structure was found for the trimer, which explains the thermal stability of this species. © 1995 John Wiley & Sons, Inc.     

Synthesis of thiol chelating resins and their adsorption properties toward heavy metal ions

A series of chelating resins, derived from a macroreticular styrene-divinylbenzene (2%) copolymer beads grafted with various poly(ethylene glycols) HO? (? CH₂? CH₂? O? )_n? H(n = 0, 4, 9, 13) and containing thiol groups as chelating functions, have been synthesized in a three-step reaction sequence. The structure of the functionalized resins was confirmed by IR spectrophotometry, elemental analysis, and differential scanning calorimetry. The complexation behavior of these thiol resins was investigated towards Hg(II), Cu(II), and Pb(II) ions in aqueous solution by a batch equilibration technique. The influence of pH on adsorption capacity was also examined. The adsorption values for metal ions' intake followed the order Hg(II) > Cu(II) > Pb(II). The affinity of these polymers towards Hg(II) ions was so high that the total mercury level in the liquid decreased from 20 ppm to below 10 ppb after 2 h of treatment. Polymers can be regenerated by washing with a solution of hydrochloric acid (6N) and 10% by weight of an aqueous solution of thiourea. © 1994 John Wiley & Sons, Inc.     

绝压传感器温漂补偿及性能仿真

分析了扩散硅绝对压力传感器的静态特性,提出了线性校正和零点校正方案,并利用Matlab软件对其性能进行了仿真,结果表明:解决了该类绝对压力传感器温漂的补偿问题,用廉价的压力敏感元件实现了对真空压力分辨到1Pa的测量.     

聚联苯醚二甲酰十二碳二胺的热降解过程与机理

利用热重法研究了半芳香尼龙聚联苯醚二甲酰十二碳二胺(PA12-O)在N2气氛中以不同速率β升温时的热降解过程及热降解动力学.结果表明,PA12-O的热降解是一步反应,随着β的增大,降解温度呈指数关系升高.其起始平衡降解温度为439.4℃,终止时的平衡降解温度为468.33℃,最大降解速率时的平衡降解温度为459.17℃.为确定PA12-O的热降解机理,比较了用Kissinger、 Flynn-Wall-Ozawa和 Coats-Redfern方法求得的PA12-O的热降解表观活化能,证明PA12-O的热降解机理为减速类型.